I just finished installing Windows 8. It's my first time with duel booting, so I accepted all the defaults and installed Win8. When the installation finished, I rebooted, but I am now taken directly to Windows with no option for the alternate OS. Windows Advanced Properties only lists Windows as an available OS. How do I enable Ubuntu to boot?

I have Ubuntu on my laptop. Now I want install Windows 7 in a dual-boot. How can I do this? I can't lose my Ubuntu files, and I'm afraid that I might break . Go  for UEFI only!


Let $x\in\mathbb R$ and suppose that $2^x,3^x$ and $5^x$ are all integers. Does it imply that $x$ is also necessarily an integer?  I read somewhere that the answer is "Yes" and a proof is known, but I haven't seen a proof and was not able to prove it myself. Could you please help me to find a proof?

Conjecture:     There does not exist a non-integer $x$ such that      $$2^x=a$$ $$3^x=b$$ $$5^x=c$$      where $a,b,c$ are all integers.     I'm aware that the similar question      There does not exist a non-integer $y$ such that      $$2^y=A$$ $$3^y=B$$      where $A,B$ are all integers.   is a famous unsolved problem.  (evidence in the corrolaries  or )  My idea was that the addition of the condition $5^x$ made the problem easier and therefore solvable.


I am building a tool in Java to fetch all the metadata from Salesforce using the Tooling API.  For Ex: I want to fetch all the profiles details including object-permission, field-premission, recordtype settings, tab setting etc. using Tooling API.  Can anyone suggest me how to fetch all these details using Tooling API?

I am attempting to use the Tooling API to retrieve all the data for a particular profile. According to the Tooling API documentation from v32 there is a Profile object which contains a set of ProfileMetadata. I am running the following anonymous code:  HttpRequest req = new HttpRequest(); req.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionID()); req.setHeader('Content-Type', 'application/json'); req.setEndpoint('https://na11.salesforce.com/services/data/v32.0/tooling/sobjects/Profile/00eA0000000WrUv'); req.setMethod('GET'); Http h = new Http(); HttpResponse res = h.send(req); system.debug(res.getBody());   The profile being referenced is a custom profile with permissions on objects etc however the debug output is as shown at   As you can see certain data is not coming through (objectPermissions is what I need out of this) and I wondered if anybody had any idea how to get that data? Thanks.


this method keeps returning Null for some reason  it should create and return either a .jpg or a .mp4 file  private static File getOutputMediaFile(int type) {     // External sdcard location     File mediaStorageDir = new File(             Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),             Config.IMAGE_DIRECTORY_NAME);     // Create the storage directory if it does not exist     if (!mediaStorageDir.exists()) {         if (!mediaStorageDir.mkdirs()) {             Log.d(TAG, "Oops! Failed create "                     + Config.IMAGE_DIRECTORY_NAME + " directory");             return null;         }     }     // Create a media file name     String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss",             Locale.getDefault()).format(new Date());     File mediaFile;     if (type == MEDIA_TYPE_IMAGE) {         mediaFile = new File(mediaStorageDir.getPath() + File.separator                 + "IMG_" + timeStamp + ".jpg");     } else if (type == MEDIA_TYPE_VIDEO) {         mediaFile = new File(mediaStorageDir.getPath() + File.separator                 + "VID_" + timeStamp + ".mp4");     } else {         return null;     }     return mediaFile; }   i can't figure out why? i call for it here in order to obtain a file Uri ontop of the specified action above  private void captureImage() {     Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);     fileUri = FileProvider.getUriForFile(Camera.this,             "com.company.example.provider",             Objects.requireNonNull(getOutputMediaFile(MEDIA_TYPE_IMAGE)));     intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri);     startActivityForResult(intent, CAMERA_CAPTURE_IMAGE_REQUEST_CODE); }   but as soon as captureImage() gets to FileProvider.getUriForFile() it crashes due to Null Pointer Exception  2020-01-16 14:39:52.766 13603-13603/com.company.example E/AndroidRuntime: FATAL EXCEPTION: main     Process: com.company.example, PID: 13603     java.lang.NullPointerException         at java.util.Objects.requireNonNull(Objects.java:203)         at com.company.example.Camera.captureImage(Camera.java:76)         at com.company.example.Camera.lambda$onCreate$0$Camera(Camera.java:44)         at com.company.example.-$$Lambda$Camera$TibLnS7dWo_dEUw9GC45GOADOCo.onClick(Unknown Source:2)         at android.view.View.performClick(View.java:6274)         at android.view.View$PerformClick.run(View.java:24859)         at android.os.Handler.handleCallback(Handler.java:789)         at android.os.Handler.dispatchMessage(Handler.java:98)         at android.os.Looper.loop(Looper.java:164)         at android.app.ActivityThread.main(ActivityThread.java:6710)         at java.lang.reflect.Method.invoke(Native Method)         at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:770)

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I am using PHP Mailer to send invoices to my clients. Some clients have adressed the problem that my mails land in their spam folders (I cannot disprove it). I read several articles and posts here and tried to orient my settings according to .  Since there are a lot more suggestions, of which I am not sure about, I want to check on what I am currently deploying and what actually makes sense.  What I checked:   I use mostly plain text, very less html (just <p>) and no css The IP adress of the mail server matches the adress of my domain  I am on no blacklist (looked it up on several pages referenced in high-voted posts here) I always send emails from the domain of my website, no other domain shows up in any parts of the mail (like reply to etc.)   What I did not check / What I'm not sure about:   Authentication methods, such as SPF or DKIM. As a not advanced user concerning programming emails I do not know how to set these things up - is it still advisable/acceptable operating without? I only use my main-domain for sending my e-mails rather than an additional email domain. Some suggested to use this extra email domain in case I lose reputation. Is it recommended to use extra email domains for this? Is it possible to check if my mails actually land in the spam folder e.g. with the PHP Mailer or do I need third party email services (like "Mailgun")?  I do not always have the full name for the To Field, is it still advisable to add the last name (without first name) to the email adress?   My PHP Mailer lines (do I use everything that is recommended?):  require_once('../PHPMailer/class.phpmailer.php'); iconv_set_encoding("internal_encoding", "UTF-8"); $mail = new PHPMailer(); $mail->CharSet = 'UTF-8'; $mail->isSMTP();                              $mail->Host = 'xxx';   $mail->SMTPAuth = true;                           $mail->Username = 'xxx';                 $mail->Password = 'xxx';                         $mail->SMTPSecure = 'tls';                            $mail->Port = 25;  $mail->setFrom('xxx', 'Potatoe'); $mail->addAddress('xxx', 'AnotherPotatoe');    $mail->addReplyTo('xxx', 'xxx'); $mail->addCC('xxx');  $mail->addAttachment('/xxx/xxx.pdf');          $mail->isHTML(true);                                $mail->Subject = 'xxx'; $mail->Body    = 'xxx'; $mail->AltBody = 'xxx';

This is a tricky one and I've always relied on techniques, such as permission-based emails (i.e. only sending to people you have permission to send to) and not using blatantly spamish terminology.  Of late, some of the emails I send out programmatically have started being shuffled into people's spam folder automatically and I'm wondering what I can do about it.  This is despite the fact that these particular emails are not ones that humans would mark as spam, specifically, they are emails that contain license keys that people have paid good money for, so I don't think they're going to consider them spam  I figure this is a big topic in which I am essentially an ignorant simpleton.


I have a entry level dslr (Nikon D3300) and was practicing long exposure photography. I noticed one behviour from the camera and was inquisitive whether this can be tweaked in any way:   I kept the shutter open for 2 minutes. When I clicked the shutter the release the second time to close the shutter, the camera took another 2 minutes to process and save the image. I tried this for multiple timings and observed and the longer the shutter is kept open, more is the time required by camera to process and save the image. Its almost 1:1 ratio. Is that expected?   I am going on a trip where I am expecting to take star photos. I am planning to keep long expose (20min +) to capture rotation of earth in the star. My concern is after keeping shutter  open for 20 minutes, if the camera takes another 20minutes to save the image, I would get limited time to multiple shots. As one photo would take close 40 minutes to store in my camera. It would get frustrating waiting everytime to wait for camera to save the image. It would even feel worse if after waiting for so long, the imagedoes not meet your expectation.  Is there a way I can improve the time if takes to process and save the image after I have released the shutter? If possible how to do so and are there any repercussion to image quality if thats done?  Thanks

Last night I took some night sky shots, and I've noticed that with long exposure times (15s, 30s) the time it took to store the images in the camera memory card (jpeg) took roughly as long?  The actual file size is fairly small at 1 to 3MB per file.  Any idea why this is?


I am trying to make topographic maps for some countries and show only those countries. I already created reliefs from SRTM-data and imported lake and river data from Natural Earth. Now I want to delete all raster and shape information that is out of the country (in my example down there, Peru). The country is another shapefile from Natural Earth.  Long story short: How do I delete all the stuff out of Peru?

In QGIS I would like to clip a raster precipitation layer using an admin boundary layer that is vector data. However the Geoprocessing tools seem to be usable only for vector data. How can I clip this precipitation layer?


Background   My laptop has three disk drives, two of which are SSDs. The system drive is a 512 GB Samsung SSD 850 PRO, while the other SSD is a 64 GB Plextor M5M. Needless to say, the M5M is significantly slower than the 850 PRO, especially with writes. (Overall read and write performance are about 80% and 35% of the 850 PRO, respectively.) The system runs Windows 8.1 Pro and has 24 GB of memory. Pagefile size is presently set to a minimum of 1 GB and a maximum of 8 GB. While it's exceedingly rare for the system to run low on memory, this question is still relevant because some applications rely on the pagefile to function correctly regardless of the amount of physical memory available.   The question   I'm considering placing the pagefile on the M5M. However, because Windows complains that it may not be able to save a crash dump in the event of a BSOD if there is no pagefile on the system volume, it might be a good idea to leave a small pagefile on the SSD 850 PRO. (See the proposed configuration below.) I understand that doing this would slow paging operations due to the lower I/O performance of the M5M. The upshot of this, however, is that contention with system and application I/O on the main disk is avoided. As such, I'm not sure as to the practical performance impact when heavy paging occurs. I'm not really worried about NAND endurance. The SSD 850 PRO has extremely high endurance because of the underlying 3D V-NAND technology, and the M5M isn't used that much. Should I use the pagefile configuration below? What other options should I consider that might be better?

I'm considering getting an SSD drive to run as the primary OS partition.  As I understand, this should provide a substantial improvement in performance.     My question is this: Should I leave the swap file on that drive?     The swap partition will be largely random seeks and so should benefit from the speed.  On the other hand, it will be constantly written to which will wear out the drive faster.


I am able to access my Gmail account on my Android, but I want to access it using my laptop. I can't do that because I don't know my password and when I go to reset it, it asks me to input the phone number associated with the account.   The problem is that I no longer have that phone number. What can I do to reset my Gmail password?

I have forgotten the password or username for my Google account, or I'm unable to access my account for other reasons.  How can I recover my account?  (This Q&A is meant as a general description for all Google and Gmail username/password questions. See: )


For all $n \ge 1$ use mathematical induction to establish the divisibility of the statement:    $$ 15 \mid 2^{4n}-1 $$   So first i substituted $1$ in and proved the statement to be true by example  then for my assumption I put $k$ in for $n$ and for my proof so far I have:  \begin{align*} 15 &\mid 2^{4(k+1)}-1 \\ RHS & =2^{4k+4} -1 \\ &=2^4 \cdot 2^{4k}-1 \end{align*}  Is the splitting in the last step correct? Also how do I/where do I substitute my induction hypothesis into the equation? step by step explanation please!

For all $n\ge1$, use mathematical induction to establish each other the following divisibility statements:   $$5\mid2^{4n}-1$$    I was wondering if someone could help me with the set up of this proof. I only have done proofs with mathematical induction when I am given a series of numbers and I can incorporate my induction hypothesis in for one of my terms in the series.   Step by step explanation please?


I am new in Python. I was trying to use a variable for selecting a feature instead of giving a direct input. My code sample will explain it better:  import arcpy from arcpy import env env.overwriteOutput = True env.workspace = "H:/shp"  #variables parcel = "parcel.shp" parcel_Layer = "parcel_Layer"  Make Feature Layer arcpy.MakeFeatureLayer_management(parcel, parcel_Layer, "", "", "FID FID VISIBLE NONE;Shape Shape VISIBLE NONE;OBJECTID OBJECTID VISIBLE NONE;ACCOUNTID ACCOUNTID VISIBLE NONE;PropID PropID VISIBLE NONE")  parcel_Layer_selattr = arcpy.SelectLayerByAttribute_management(parcel_Layer, "NEW_SELECTION", "\"PropID\" = 142855")   This code works fine as long as I enter the property ID directly ("\"PropID\" = 142855"). But when I declare the PropID as a variable, it doesnot work. Here is the code sample:  import arcpy from arcpy import env env.overwriteOutput = True env.workspace = "H:/shp"  #variables parcel = "parcel.shp" parcel_Layer = "parcel_Layer" x = 142855 Make Feature Layer arcpy.MakeFeatureLayer_management(parcel, parcel_Layer, "", "", "FID FID VISIBLE NONE;Shape Shape VISIBLE NONE;OBJECTID OBJECTID VISIBLE NONE;ACCOUNTID ACCOUNTID VISIBLE NONE;PropID PropID VISIBLE NONE")  parcel_Layer_selattr = arcpy.SelectLayerByAttribute_management(parcel_Layer, "NEW_SELECTION", "\"PropID\" = x")   This is not working. it gives me this error msg:   Runtime error  Traceback (most recent call last):   File "<string>", line 1, in <module>   File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\management.py", line 6435, in SelectLayerByAttribute     raise e ExecuteError: ERROR 000358: Invalid expression Failed to execute (SelectLayerByAttribute).   What I am doing wrong?

I'm trying to iterate through a feature class and select each feature one by one by using the OBJECTID field. When I use a single value, the SelectLayerByAttribute works, but how do I compare the OBJEECTID to a variable that increases in count through the loop. The program is then suppose to create a layer for each feature in the feature class. This is what I have so far:  import arcpy import os arcpy.env.workspace = "C:\Users\Daimon Nurse\Desktop\DFMPROJECT\DFMPROJECT.gdb" arcpy.env.overwriteOutput=True inlayer = "C:\Users\Daimon Nurse\Desktop\DFMPROJECT\DFMPROJECT.gdb\ZonesPolyline"   with arcpy.da.SearchCursor(inlayer, ("OID@", "SHAPE@AREA")) as cursor:     i = 1     for row in cursor:         print("Feature {0} has an area of {1}".format(row[0], row[1]))         outlayer = "ZonePolygon"         arcpy.MakeFeatureLayer_management (inlayer, outlayer)         arcpy.SelectLayerByAttribute_management (outlayer, "NEW_SELECTION", """           "OBJECTID" = 1 """)         output = r'C:\Users\Daimon Nurse\Desktop\Grounds Project\DFMGROUNDS.gdb'         outfile = os.path.join (output, i)         arcpy.CopyFeatures_management(outlayer, outfile)         print i         i = i + 1


Is there any proper way to customize Drupal.ajax.prototype.beforeSend and Drupal.ajax.prototype.success functions? I just wanted to add additional effect to the inserting and removing of Throbber container, but I couldn't find any way to achieve this. Then I created a new js file and copied the whole functions and modified them. After that I added the file with drupal_add_js() with additional check, like this:  if (!path_is_admin(current_path())) {     drupal_add_js(drupal_get_path('theme', 'carroza') . '/js/custom.js', array('type' => 'file', 'group' => JS_THEME));   }   This is working fine, but I think this kind of approach is wrong and is not convenient.

I need to add my own little if's and checks in 3 functions inside   misc/ajax.js (   Drupal.ajax.prototype.beforeSend,   Drupal.ajax.prototype.success,   Drupal.ajax.prototype.error )   How can I override them in my module? I can't find a manual and it's not in Examples for Developers. Sorry if it seems a dumb question, but I'm a php developer - I can work with js, but I'm not so fluent with it.   Can I simply write it in my module's js file? If 2 or 3 modules needs to modify them, how to avoid conflicts?


I recently got a new computer. I want to do a backup of everything and save it on an empty disc. So that if in future my computer fails, I can just use this disc and re-install Windows, all my drivers and whatever was on my comp when I first bought it (i.e. back to factory settings).  This computer was actually assembled by my friend's friend and I am not at all IT savvy. This seems like the best way for me to 'reformat' my comp without going through the hassle of finding someone who could reformat for me.  I want to know if this is possible?   Is the solution to this to create a System Image and then saving it on an empty disc?  I am currently using Windows 7.

I have a couple of computers running Windows XP and they all have the same software installed on the same hardware. I would like to create one image, so that in case a user's computer dies I can just restore it with the image. That will save me time by not installing Windows all over again and all the software.  Also, every user has their own favorites, desktop etc. I would like to back that up too, so that after an image restoration I can restore their favorites, desktop etc.


Ubuntu 16.04  #!/bin/bash  site="hello" wDir="/home/websites/${site}/httpdocs/"  for file in $(find "${wDir}" -name "*.css") do    echo "$file"; done exit 0;   shellcheck warns me even if I define the start directory but the script works just fine.  root@me /scripts/ # shellcheck test.sh  In test.sh line 6: for file in $(find "${wDir}" -name "*.css")             ^-- SC2044: For loops over find output are fragile. Use find -exec or a while read loop.

This question is inspired by    I see these constructs  for file in `find . -type f -name ...`; do smth with ${file}; done   and  for dir in $(find . -type d -name ...); do smth with ${dir}; done   being used here almost on a daily basis even if some people take the time to comment on those posts explaining why this kind of stuff should be avoided... Seeing the number of such posts (and the fact that sometimes those comments are simply ignored) I thought I might as well ask a question:  Why is looping over find's output bad practice and what's the proper way to run one or more commands for each file name/path returned by find ?


My .timer file located in ~/.config/systemd/user doesn't show in output of systemctl --user list-timers --all command unless i enable it. Is it normal for this command to not show disabled .timers alongside enabled ones? I cannot enable the .timer without an [Install] section because of The unit files have no installation config error. According to freedesktop.org documentation:  Timer units will automatically have a dependency of type Before= on timers.target  Does this mean that i do not have to enable my .timer for it in order to work? If i do need to enable my .timer: I believe that default.target is what software which is to be executed after successful user login is WantedBy. I also believe that the user systemd instance is started by pam_systemd, which i believe happens before default.target. So it seems to me that if i use default.target the timer will be activated after login. If i use OnStartupSec in this case, will it correctly count the time from the startup of the systemd user instance? On the other hand, if i use timers.target, since this is a user timer, will it be activated before login and start counting the seconds from its activation time, or it will just register and start counting time only after systemd --user is started?

In various examples, I have seen all of these different choices suggested:   WantedBy=timers.target WantedBy=multi-user.target WantedBy=basic.target WantedBy=default.target WantedBy=mytimer.target (custom user-defined name)   However, in the examples I have found, no further explanation is offered.  The following pages also don't offer any explanation of WantedBy:       I want to understand one simple* method I can use when needed to write a systemd timer instead of a cron job.   * Setting up a cron job is 1 line. Systemd timers involve writing two files and running one or two systemctl commands. But that fact alone is not necessarily what makes systemd timers harder than cron in my experience -- it's the multitude of options and the (seeming) lack of clear documentation with simple examples that are fully explained.


This seems like such a simple task, yet after researching how to execute it in QGIS I've been unsuccessful.  I'm merely trying to rename columns in my attribute table.  My existing field is currently named "employment", and I would like to rename it "BG_Desc".    I've read the "table manager" plug-in will do this, but it appear the plug-in is no longer available for version 3.0.   I've used the "replace" tool under "String" in the field calculator, but it does not work when I enter the following:  replac("employment",employment","BG_Desc")   Suggesstions?

I would like to rename some fields in my attribute table:  Like rename "XRF_N3"in something else. It seems quite a easy issue but I don't find any information about how can I do that.


I'm brand new to Ubuntu (and linux all together). I just installed Ubuntu 12.10 on my Lenovo S10e, and I'm trying to play movies that I loaded from my external HD onto the netbook. I've tried 4 different files, but none are working in either the standard Ubuntu video player or VLC. The only thing that shows up is the VLC cone in the display window.   I have no idea if the graphics driver was installed or not, and if it wasnt I dont know how to do that in Ubuntu.   I have 1.5gb of ram installed, so I doubt thats the issue. Anyways, i'm not very computer saavy, but I'd appreciate any help. Thanks you in advance.

I would like to know how can I enable video and audio codecs not included by default on Ubuntu. Thanks!


If I want to estimate $E_P(f (x))$ where f is some function, I can produce samples $\left\lbrace x^{1} , \dotsc , x^{L}\right\rbrace$ from the Markov chain (with a stationary distribution matching $P$ ) and have the following estimator:  $$E_{MCMC} (f (x)) = \frac{1}{L} \sum_{l=1}^{L} f \left(x^{l} \right).$$  The samples produced by MCMC are non-i.i.d.. It is common to analyze the effective sample size (ESS) of an MCMC sampler, i.e.,   How should I find the ratio of the sample of size $S$ produced by MCMC to its effective size (the ratio between number of samples produced by the chain to the number of perfect i.i.d. samples both of result into estimators that have same variance)?

I've found two definitions in the literature for the autocorrelation time of a weakly stationary time series:  $$ \tau_a = 1+2\sum_{k=1}^\infty \rho_k \quad \text{versus} \quad \tau_b = 1+2\sum_{k=1}^\infty \left|\rho_k\right| $$  where $\rho_k = \frac{\text{Cov}[X_t,X_{t+h}]}{\text{Var}[X_t]}$ is the autocorrelation at lag $k$.    One application of the autocorrelation time is to find the "effective sample size": if you have $n$ observations of a time series, and you know its autocorrelation time $\tau$, then you can pretend that you have  $$ n_\text{eff} = \frac{n}{\tau} $$  independent samples instead of $n$ correlated ones for the purposes of finding the mean.  Estimating $\tau$ from data is non-trivial, but there are a few ways of doing it (see ).  The definition without absolute values, $\tau_a$, seems more common in the literature; but it admits the possibility of $\tau_a<1$.  Using R and the "coda" package:  require(coda) ts.uncorr <- arima.sim(model=list(),n=10000)         # white noise  ts.corr <- arima.sim(model=list(ar=-0.5),n=10000)    # AR(1) effectiveSize(ts.uncorr)                             # Sanity check     # result should be close to 10000 effectiveSize(ts.corr)     # result is in the neighborhood of 30000... ???   The "effectiveSize" function in "coda" uses a definition of the autocorrelation time equivalent to $\tau_a$, above.  There are some other R packages out there that compute effective sample size or autocorrelation time, and all the ones I've tried give results consistent with this:  that an AR(1) process with a negative AR coefficient has more effective samples than the correlated time series.  This seems strange.    Obviously, this can never happen in the $\tau_b$ definition of autocorrelation time.  What is the correct definition of autocorrelation time?  Is there something wrong with my understanding of effective sample sizes?  The $n_\text{eff} > n$ result shown above seems like it must be wrong... what's going on?


I am struggling to find such languages $L_1$, $L_2$, and $L_3$ such that $L_1\subset L_2\subset L_3$ where $L_1,L_3\notin$ RE and $L_2\in$ R.  I know they exist, I need help finding them.

I am struggling to find such languages $L_{1}$, $L_{2}$, and $L_{3}$ such that  $$ L_{1} \subseteq L_{2} \subseteq L_{3} $$ where $L_{1}, L_{3} \notin  \mathbb{R}$ and $L_{2} \in  \mathbb{R}$.  I know they exist, I need help finding them.


Base is the base class and Derived is the derived class.  Base* p = new Derived; delete p;   Let's assume that the base destructor is not virtual. Does this cause memory leak, if yes, why? And what would be the solution to fix it?

I have a solid understanding of most OOP theory but the one thing that confuses me a lot is virtual destructors. I thought that the destructor always gets called no matter what and for every object in the chain. When are you meant to make them virtual and why?


So my core understanding of what a contour integral is may be wrong so the question I'm attempting to ask is what is the complex output value of a contour integral 'defining'. I understand well enough that for closed paths not containing singularizes, the contour integral will equal zero and that if it does contain singularities the it may produce a complex valued output given in the form of $\displaystyle 2\pi i\ f( a)$ for cases that can be evaluated using the Cauchy integral formula. I have no trouble evaluating them mathematically but I have zero idea about why it's even useful to compute a contour integral. If not defining an 'area', what is it actually telling us? How do we use that information? Is their a good visual explanation for why a contour integral is non zero for contours around a singularity?

I am very confused on what path and contour integrals actually represent. I tried looking for an answer on Google but the only examples were related to Quantum Mechanics. For instance, real Riemann integrals can be thought as "the area under the curve". What about path/contour integrals? Also, is there a difference between path and contour integrals, or are they the same thing? I've been thinking of contour integrals as path integrals where the path is a "closed loop", but I'm not sure if that's the case. It's all so confusing, and not being able to visualise these concepts makes it feel like I'm just memorising formulas and theorems without any reason. I have been thinking about path integrals as integrating over a curve in three dimensions. For example, in an $xyz$ coordinate system (with $y$ pointing “up”), we have a path on the $x$-"$z$" plane and integrate over that path. That is, instead of integrating over and along "$y=0$", we integrate over a certain path. But I don't know if this is a correct way to think of path integrals. This issue has been frustrating me a lot because I'm now studying theorems that involve path/contour integrals and I just can't understand what they really do or mean. By path integral I mean $$\int_{\gamma\vert_{[a,b]}}f(z)\hspace{0.2em}dz = \int_{a}^{b}f(\gamma(t))\cdot\gamma'(t)\hspace{0.2em}dt$$ where $f:U\subseteq\mathbb{C}\rightarrow\mathbb{C}$ is a function that satisfies all conditions for complex integration and $\gamma:[a,b]\rightarrow U\subseteq\mathbb{C}$ is at least a piece-wise regular path. Any help would be appreciated.


The other day a comment of mine had three helpful votes. These have not been credited in the helpful flags total in the profile. There was at least one other occurrence a month or two ago where one vote was not credited. Is this a stack bug or are helpful votes only selectively credited?

I don't see "Helpful" in the list of things I can do when I press the flag link.   In my profile page I saw "6 helpful flags."  How do I earn these flags?  May I make them on other peoples' posts or comments?   This is what I am talking about:


I understand that we should use virtual destructors in base classes to ensure proper resource disposal, because it guarantees the inheritance chain will be observed and all parent destructors will be called when destructing an object. That being said, do we also need virtual destructors in base classes when both the base class and any subclasses use only the default destructor? Example:  class Printable {   virtual std::string print(); };  class A : public Printable {   int foo;   bool bar;   std::string print() override; }  class B : public Printable {   std::vector<int> foo;   std::string print() override; }   There are no resources being managed, and all destructors are implicitly default. Is it still advisable to specify a virtual destructor in Printable?


Just realized the TP-Link Archer T2U (ID 148f:761a) I just bought does not plug and play on Kubuntu 20.04 Exact product is  The box specifically says linux support is for kernel 2.6-3.16 while Kubuntu 20.04 is far advanced with 5.4.x Is there some sort of solution that can be applied to make this dongle work on this old machine which currently does not have internet access so sudo apt-get ... is less comfortable. if I could only download a thingy/driver and put it on a thumb-drive and plug that thumb-drive into the kubuntu 20 machine and install that thingy/driver and things would work, that would be awesome.

I recently got a wireless adapter (TP-Link Archer T2UH V1). After plugging it in, I found out that the drivers for Linux are not native on Ubuntu. They do, however, have the drivers available for download (in the form of compilable/ makefile). What I am not sure of is how to install these drivers. I know that I need to build the drivers, place things where they need to be, and tie things together with the kernel. I am not sure how to do this, however, and need some help.  TL;DR: I need to know the terminal commands to install these drivers.  Driver/Device info:   Output of lsusb:  Bus 003 Device 004: ID 148f:761a Ralink Technology, Corp.


I made a bootable USB with Ubuntu and I want to try a bit of Linux. I have an SSD in my laptop which shows only one partition. Now, I want to be able to choose which OS to run when my machine boots up and I don't know if I should just install Ubuntu when I reset my laptop and will that way everything I have on windows still be there or I need to make another partition. So I just want to be able to run both OS's without any of my files being erased. Thanks.

I'm absolutely new to Linux. I would like to know how to install Ubuntu alongside the pre-installed Windows 8+ OS.  Should I do it with Wubi, or through the Live USB/DVD?  What steps do I need to take to correctly install Ubuntu?


I need to copy the text that is inside of ~p~ tag, I've tryed using this code:  HTML:
Text to copy
 <button onclick="copyFunction()">Copy text</button>   JS:  function copyFunction() {    var textToCopy = document.getElementById("copy");    textToCopy.select();    document.execCommand("copy");    alert("Copied the text: " + textToCopy.value); }   But it didn't worked.

What is the best way to copy text to the clipboard (multi-browser)? I have tried: function copyToClipboard(text) {     if (window.clipboardData) { // Internet Explorer         window.clipboardData.setData("Text", text);     } else {         unsafeWindow.netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");         const clipboardHelper = Components.classes["@mozilla.org/widget/clipboardhelper;1"].getService(Components.interfaces.nsIClipboardHelper);         clipboardHelper.copyString(text);     } }  But in Internet Explorer it gives a syntax error. In Firefox, it says unsafeWindow is not defined. A nice trick without using :


I am trying to show that $|\Bbb {R} \times \Bbb {R}| \leq |\Bbb {R}|$.  I don't know how to define $f:\Bbb {R} \times\Bbb {R} \rightarrow \Bbb {R}$ in a way that would make $f$ injective.  My professor gave us the hint that $(0,1) \sim \Bbb {R}$ would imply that $|(0,1) \times (0,1)| \leq |(0,1)|$, but I don't understand how that is helpful here.

Is there an injective function $f :\mathbb{R}^2\rightarrow\mathbb{R}$?  I approached this problem from the perspective of $f^{-1}$, from which I showed there exists a surjective function $f^{-1}:\mathbb{R}\rightarrow\mathbb{R}^2$. Would this imply that there exists an injective function for the inverse mapping?


It's just that the children are worried and so am I. Is it safe?

EDIT Dec 4 -  We're doing it live! Please post bugs or concerns as questions tagged [top-bar]  We have rolled out our 95% completed top bar for feedback.  Note:   We are still adding a few final features, so if you have a request for a feature that is not there you might hold off on that for a day or two Yes, the bar is black1. Also give that a day or two to sink in.   I also want to specifically address the meta/main/chat links.  I'm very aware that many of you like having the links at the top of the page and that this new version is different.  The thought process behind moving these links is that the "site switcher" should be an automatic place to go when you are on a site and want to go to another one. If you haven't already developed the muscle memory for these links, getting between them required a bit of a cognitive load: You must first decide that you want to switch sites and then you have to decide which area to go to to switch.  Also, we find that less familiar users aren't entirely clear what a standalone link that says "main" or "meta" actually does... Not to mention that it hurts my UX sensibilities that we are dynamically changing links in an element that should be fixed.  It is true that we have added a click in the process, but we have also removed a lot of clicks for other common actions that are much more frequent than switching between main and meta.  All I ask is that you give it a few days and see if the new "switch sites at the top left" paradigm grows on you.  What do you think?  1.  points out that technically it's not quite black.


I want to include the following expression without any changes in my LaTeX document:   RES_0.5_SE_5   If I just type like that, LaTeX wants it to be math mode because of the underscores. If I use   \verb|RES_0.5_SE_5|   the text has a different font.  Is there a command to just use ignore math symbols?  Thanks!

How can I produce the text Word_one_two in LaTeX?  I tried:  Samp\_Dist\_Corr   But, it doesn't quite look right. Also, I want it in the typewriter font, so actually, I'm doing:  \texttt{Samp\_Dist\_Corr}   I find it looks a bit like the underscore is merging in to the bottom of the "D", but maybe it's just because of the typewriter D?


Hope you don't mind my question. I would like to know what is the last version of Ubuntu for desktop with Intel processor. I check , the last is Ubuntu 18.10 AMD64. Appreciated if someone can provide with a downloadable link.

I need to find the 32-bit version, and all I keep finding is the 64-bit. Can anyone provide me with a link?


If we have a dir/file setup like the following  var   |-->usr   |    |-FileA   |    |-FileB   |    |-FileC   |    |-FileD   How can I move FileA and FileD without specifying the path twice like in the following cmd?  mv /var/usr/FileA /var/usr/FileB /home

I know how to rename files in Unix:  $ mv ~/folder/subfolder/file.txt ~/folder/subfolder/file.sh       ^-------this part------^    ^------this part-------^   It takes too long time to repeat ~/folder/subfolder/file twice.  Is there a quicker way?


I am trying to read smartcards via NFC on Android. I had a solution working in Eclipse, but after migrating to Android Studio it only works once, reads all the data from the card, but then freezes and repeats this error over and over:  Attempt to invoke virtual method 'boolean android.nfc.Tag.hasTech(int)' on a null object reference W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.nfc.Tag.hasTech(int)' on a null object reference W/System.err:     at android.nfc.tech.IsoDep.get(IsoDep.java:61)  AndroidManifest.xml: <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="packageName"     android:versionCode="1"     android:versionName="1.0" >      <uses-sdk         android:minSdkVersion="17"         android:targetSdkVersion="23" />      <uses-permission android:name="android.permission.NFC" />      <uses-feature         android:name="android.hardware.nfc"         android:required="false" />      <application         android:allowBackup="true"         android:label="@string/app_name"         android:supportsRtl="true" >          <activity             android:name=".NFCReader"             android:label="@string/app_name"             android:launchmode="singleTask" >              <intent-filter>                 <action android:name="android.nfc.action.TECH_DISCOVERED" />             </intent-filter>              <meta-data                 android:name="android.nfc.action.TECH_DISCOVERED"                 android:resource="@xml/nfc_tech_filter" />         </activity>     </application>  </manifest>  NFCReader: public class NFCReader extends Activity {  private NfcAdapter mNfcAdapter;  @Override protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     mNfcAdapter = NfcAdapter.getDefaultAdapter(this);      if (mNfcAdapter == null) {         finish();         return;     }      if (!mNfcAdapter.isEnabled()) {         Log.e(TAG, "NFC is disabled.");     } else {     }      final Tag tagFromIntent = this.getIntent().getParcelableExtra(NfcAdapter.EXTRA_TAG);     new ReadCardTask().execute(tagFromIntent);      handleIntent(getIntent());     this.finish(); }  private void handleIntent(Intent intent) {     String action = intent.getAction();      if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {         String type = intent.getType();         if (MIME_TEXT_PLAIN.equals(type)) {             Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);             new NdefReaderTask().execute(tag);         } else {             Log.d(TAG, "Wrong mime type: " + type);         }     } else if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {         Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);         String[] techList = tag.getTechList();         String searchedTech = Ndef.class.getName();          for (String tech : techList) {             if (searchedTech.equals(tech)) {                 new NdefReaderTask().execute(tag);                 break;             }         }     } }  protected Void doInBackground(Tag... params) {     IsoDep tag = IsoDep.get(params[0]);     tag.connect();     // [...] transmit APDUs }  }

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I was wondering why in stackoverflow http version is not automatically redirected to https ? When I come from google search I always end up on http. But manually typing https://stackoverflow.com works, I mean ssl is installed, if so, why not to make a redirect so it will be more secure ?

So it looks like Stack Exchange now supports HTTPS (to some extent). Which is awesome! But there are a few problems, the main one being that some content is delivered over the CDN, which is plain HTTP. This causes browsers to complain about "unsecured content":


When running a stored query on data.stackexchange.com, one can select the StackExchange site to which the query should apply. This functionality is provided by a little search field with a text input that provides a “live search” for the SE sites.  When entering stacko in this field, I get (among others) the results Stack Overflow and Meta Stack Overflow. So far, so good.  But: When I select “Meta Stack Overflow”, the (colored) “Stack Overflow” icon appears, and the icon hover text says “Stack Overflow”. The query, however, is applied to “Meta Stack Overflow”. It's the same the other way round; selecting “Stack Overflow” shows the icon and label text for Meta, while the query refers to Stack Overflow.  I hope I'm not the only one to experience this. If more details should be required, please let me know.  (By the way, small UI feedback: The site selection field should probably be above the submit button, as it's an element of the form to be submitted.)

In the , the icon color for the various sites seems* incorrect: Whenever I select a main site, the icon is greyed out, and when ever I select the corresponding meta site, the icon is colored. My initial instinct was to think that the colors of the main/meta sites following the "Switch sites:" prompt should be switched. (Actually, it seems like it's just a UI thing. See the edit below.)  *Edit: Actually, the colors are technically not incorrect, since (as Jeremy Banks has pointed out) the icon shows "the other" site of the main/meta pair, and clicking on it is for switching to the respective other site. See the comment thread for some UI improvement ideas.


For an application I am writing, users have to select a folder containing some logfiles that the app works with. To make it more intuitive, I want them to be able to see the files in the folder, but still only be able to select the folder of course.  So my problem is, how can I have the Dialog open folders only, but still show the other files.  I have tried the solution from this thread,     However, it doesn't seem to work on Windows10, at least not for me and the other PCs I've tried it on.  This is what I currently have to open:  CommonOpenFileDialog dialog = new CommonOpenFileDialog(); dialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); dialog.IsFolderPicker = true; if (dialog.ShowDialog() == CommonFileDialogResult.Ok) { }

In VS .NET, when you are selecting a folder for a project, a dialog that looks like an OpenFileDialog or SaveFileDialog is displayed, but is set up to accept only folders.  Ever since I've seen this I've wanted to know how it's done.  I am aware of the FolderBrowserDialog, but I've never really liked that dialog.  It starts too small and doesn't let me take advantage of being able to type a path.  I'm almost certain by now there's not a way to do this from .NET, but I'm just as curious how you do it from unmanaged code as well.  Short of completely reimplementing the dialog from scratch, how do you modify the dialog to have this behavior?  I'd also like to restate that I am aware of the FolderBrowserDialog but sometimes I don't like to use it, in addition to being genuinely curious how to configure a dialog in this manner.  Telling me to just use the FolderBrowserDialog helps me maintain a consistent UI experience but doesn't satisfy my curiosity so it won't count as an answer.  It's not a Vista-specific thing either; I've been seeing this dialog since VS .NET 2003, so it is doable in Win2k and WinXP.  This is less of a "I want to know the proper way to do this" question and more of a "I have been curious about this since I first wanted to do it in VS 2003" question.  I understand that Vista's file dialog has an option to do this, but it's been working in XP so I know they did something to get it to work.  Vista-specific answers are not answers, because Vista doesn't exist in the question context.  Update: I'm accepting Scott Wisniewski's answer because it comes with a working sample, but I think Serge deserves credit for pointing to the dialog customization (which is admittedly nasty from .NET but it does work) and Mark Ransom for figuring out that MS probably rolled a custom dialog for this task.


I'm looking for something to concatenate all files with given extension within a directory, except one. Like:   cat *.txt !(DISCARD.txt)  > catKEPT   This should concatenate all *.txt files in directory, except DISCARD.txt.

I have a directory containing a large number of files. I want to delete all files except for file.txt . How do I do this?  There are too many files to remove the unwanted ones individually and their names are too diverse to use * to remove them all except this one file.  Someone suggested using   rm !(file.txt)   But it doesn't work. It returns:  Badly placed ()'s    My OS is Scientific Linux 6.  Any ideas?


Download the Stack Exchange app from the App Store. Run it and login with Google. Enter email and password for the Google account. Successfuly login into Google. Jump back to Stack Exchange app. Get this error message:    Notice I tried to:   Reinstall the app. iPhone restart. Clear app data.

I just switched from an iPhone 7 to an iPhone XR (both are on latest iOS version available).  When I try to login into the Stack Exchange app with my Google account it says:     Request failed   Could not perform this request with your account. Please try logging   back in. If this persist, let us know on meta.   this happens consistently.  I have 2FA enabled on my Google account if it matters.  Is this a known bug?


I have a script with the following code:  command_that_could_fail || (echo "command failed"; exit 1)   However, the exit seems to just be exiting from the sub-command formed by the second part of the line (in parentheses), not from the script itself. Any way that I can make it behave as desired, and exit from the outer script?

I have a script, that does not exit when I want it to.  An example script with the same error is:  #!/bin/bash  function bla() {     return 1 }  bla || ( echo '1' ; exit 1 )  echo '2'   I would assume to see the output:  :~$ ./test.sh 1 :~$   But I actually see:  :~$ ./test.sh 1 2 :~$   Does the () command chaining somehow create a scope? What is exit exiting out of, if not the script?


I have an .sh file that looks like   #!bin/bash exec /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/ java java -jar /home/me/myfolder/my.jar   I've made this file executable and it works fine when in the "nautilus" desktop, but when I run it on just normal desktop (Ubuntu 14.04) it only opens with gedit. I have also tried opening it with Java 7 and Java 6, but it does not give me the option to run in terminal. Also when i'm in the terminal and cd to the folder containing the .jar file and run it that also works fine. What I'm looking for is a way to just double click my .sh file without having to go to nautilus first. Is this possible?  Sorry if this is a duplicate, but I cant find the answer I'm looking for.

I have tried right clicking on the file selecting properties and then the permissions tab and setting it to execute. However, when I double click the file it opens in gedit. What do I do?


I have happened upon this use of a in a  on english grammar. It is at around 7 minute and 35 second. Here it goes:     Fine wines, and a knowledge thereof, are luxury few can afford.   I am aware that when a mass nount used with an adjective then an article is needed, but there a mass noun is alone. Tell me please why the teacher decided to use a before the word. Does a mean a little there?

I'm trying to pass a test on "Articles exercise" as they call it . Reviewing my answers I got stuck about the two I posted on the picture below.  As I understand both words are uncountable (according to the ), so it looks like (or said for example ) I can't say a/an with an uncountable noun.  But this test says the opposite. Is there some trick? Or am I just dumb? Please help me to understand why I need to use "a" article in these cases?        We need a secretary with ____ good knowledge of English.          a  (marked as the correct answer)   the     a / the     no article is needed (the answer I think is correct)        We're having ____ terrible weather.         a (marked as the correct answer)     the     a / the     no article is needed (the answer I think is correct)


I'm a new user of Latex and still trying to figure it out. Currently I have a problem where if I want to have a subscript which contains more than one letter, the spacing between the letters is too large. Namely, writing $\hat{\tau}_{eff}$ results in:    What would be the best way to bring "eff" closer together?

Is there something I can add to the preamble of my document such that multiple letters without spacing in a Math environment (such as $NP$) do not have extra spacing between them and are not considered multiple distinct variables? Right now, I have to use $\mathit{NP}$ to prevent any extra spacing, but I feel that it is more natural to add a space between the letters if they are a different variable ($N P$). For example, if I want the multi-letter variable NP, I want to be able to say $NP$ which would automatically be replaced by $\mathit{NP}$. If I want N and P to have the proper inter-variable spacing, I want to do that only when they are separated by a space, like so: $N P$. Is there a way to achieve this? Would it break something that I'm unaware of? Edit: Here's a screenshot that shows what I mean:  So basically, is it possible for line 1 to automatically give me line 3 and for line 2 to give me line 2?


I have a existing table in which i am adding a column as NgoId whose datatype is int. I want to add as NOT NULL to the column .  When I'm adding this I am getting the following error:     Unable to modify table.    Cannot insert the value NULL into column   'NgoId', table 'CSR.dbo.Tmp_tbl_post_category'; column does not allow   nulls. INSERT fails. The statement has been terminated.   Please help how to add the column with NOT NULL.

What's the best way to add columns to large production tables on SQL Server 2008 R2? According to Microsoft's books online:     The changes specified in ALTER TABLE are implemented immediately. If the changes require modifications of the rows in the table, ALTER TABLE updates the rows. ALTER TABLE acquires a schema modify lock on the table to make sure that no other connections reference even the metadata for the table during the change, except online index operations that require a very short SCH-M lock at the end.   (http://msdn.microsoft.com/en-us/library/ms190273.aspx)  On a large table with millions of rows, this can take a while. Is taking an outage the only option? What's the best way to handle this kind of situation?


I like sweet potato and i'm trying out different recipes with it as a main ingredient. One of them is the sweet potato pudding/halwa. It tastes good, but i would like to get rid of the threads of fibre that keep getting stuck.  Please suggest how to make the pudding without the threads.  I remove the ends of the sweet potato to avoid major fibrous part. And the strings are mainly present in the middle part n not near the skin. The potato near the skin is smooth and doesnt contain strings.

Is there a way or technique to make mashed sweet potatoes less stringy? Does it just come down to potato selection or can it be improved by a technique?


Flights sharing the same flight numbers can be confusing. Why do flights sometimes share the same flight numbers? This means that one can find two flights that have the same flight number. Eg some airline might have one flight from x to y, another flight from a to b, and use the same flight number for both flights on the same date.

There's a daily flight, let's call it AB 1234 which leaves at 11am with a flight duration of more than 13 hours.  I noticed that every day, the same flight AB 1234 leaves at 11am.  It seems physically impossible for the same plane to travel 13 hours and return in about a similar amount of time to still make the next day flight.  Is it possible for two or more different planes to share the same flight number?


I am using a full fresh installed Kali Linux rolling edition. And please be specific to me while explaining the matter because I am very new-be in the world of Linux. My host OS is Ubuntu 15.10.

I've recently installed Ubuntu on Oracle's Virtualbox.  Now I want to install the guest additions.  I started up my Ubuntu guest OS, clicked "Devices" and chose "Install Guest Additions". Nothing happened, and I don't see the CD icon on my desktop.  How can I make this work?


We all know that the universe is governed by four Fundamental Forces which are The strong force , The weak force , The electromagnetic force and The gravitational force .  Now, is there any relationship between Electromagnetism and gravity?

In classical mechanics, we had Newton's law of gravity $F \propto \frac{Mm}{r^2}$.  Because of this, all laws of classical electrostatics applied to classical gravity if we assumed that all charges attracted each other due to Coulomb's law being analogous.  We can "tweak" classical electrostatics to fit gravity.  In modern physics, does the reverse work?  Can we "tweak" General Relativity to accurately describe electrostatics or even electromagnetism?


I want to execute /execute if entity @p[nbt={Inventory:[{id:"minecraft:diamond"}]}] run enchant @a minecraft:unbreaking 3  except only if the diamond has infinity on it ok I use Minecraft Java 1.16.4 and optifine

I am making a Minecraft Mini Game adventure map, and one of the levels has a /setblock command, I am using the command in a way to spawn an item in a chest (Wooden Button) I need the wooden button to have CanPlaceOn tag so it can be placed on a log. I have tried this command: setblock 294 5 -1251 minecraft:chest 0 replace {Items:[{Count:1,Slot:0,id:minecraft:wooden_button,CanPlaceOn:[log]}]}`


I am connecting a new oven with 4 wires, black, white, red & copper to an existing junction box with 3 wires, white, black & copper.  What goes where??  Any help is appreciated

I've just moved house and my clothes dryer has a four prong plug but on the wall there's a three prong socket. Do adapters exist for this? Or do I need to get a new cord for my dryer? Or is there another solution?


I can't log in to Ubuntu because by accident I deleted the passwd files. I have many important files on my hard disk of which I have no backup. How can I recover them?

I was trying to change my username and also my home directory (/home/username) and my system started to crash. I deleted the passwd file but I had a backup named passwd_bkp. I tried to rename this passwd_bkp as passwd and it did not work. No commands were being executed... I was in a terminal window.   I restarted my system and now I cannot log in. GRUB gives two options: Linux and recovery mode.   I tried to open a sessions as root but it says the filesystem is corrupted. I cannot access my files.  Did I lose all my files?


I know that one way to calculate work is force*(displacement in the direction of the force). But what reference frame does that displacement value come from? One where the object starts at rest?  Here's an example to clarify. Imagine two identical rockets in space, each with the same amount of fuel. At $t=0$, the first rocket is at rest in the observer's reference frame, and the second rocket is already moving forward at some speed. They both start their engines and burn out all of their fuel, exerting identical, constant forces. When their engines stop, the second rocket has traveled farther than the first, despite both having burned the same fuel and therefore done the same work/energy.  So in that situation, what reference frame would you use for each rocket to measure its displacement? The two rockets do indeed do the same amount of work, right? Am I misunderstanding something?

Consider a rocket in deep space with no external forces. Using the formula for linear kinetic energy $$\text{KE} = mv^2/2$$ we find that adding $100\ \text{m/s}$ while initially travelling at $1000\ \text{m/s}$ will add a great deal more energy to the ship than adding $100 \ \text{m/s}$ while initially at rest: $$(1100^2 - 1000^2) \frac{m}{2} \gg (100^2) \frac{m}{2}.$$ In both cases, the $\Delta v$ is the same, and is dependent on the mass of fuel used, hence the same mass and number of molecules is used in the combustion process to obtain this $\Delta v$. So I'd wager the same quantity of chemical energy is converted to kinetic energy, yet I'm left with this seemingly unexplained $200,000\ \text{J/kg}$ more energy, and I'm clueless as to where it could have come from.


In the first Harry Potter book, it is said that Flamel and Dumbledore invented the philosopher's stone together. It's also heavily implied that this stone is the only reason why Flamel lived so long. This means that Dumbledore is… let's say less than 200 years younger than Flamel, to be safe. But since Flamel's age is given and is somewhere in the 600s, that would mean that Dumbledore is more than 400 years old. But after the stone was destroyed, he did not die from that and it's also not said that he had a stash of the elixir. In book 5 there's even a short appearance of someone who was an examinant while Dumbledore was still in school, meaning she would have to be older than him. I would be very surprised if she also got the elixir of life. The same with Dumbledore's brother: Did he get the elixir? Or their parents and he's multiple centuries younger? Or are there other ways that wizards become many centuries old? In that case I would wonder why an elixir of life was even necessary.  The only explanations I can think of are these:   Dumbledore wasn't actually involved in creating the stone and book 1 lied. Flamel isn't actually that old and book 1 lied (and maybe others as well). Rowling is very bad at Math, much more than usual.

I apologize in advance if this is a common question, I searched for "flamel" here first and couldn't find the answer.  If Nicolas Flamel is several hundreds of years old, how did Dumbledore work on the Philosopher's Stone with him? Did he use it a bit himself?  To clarify, Flamel would've died without the PS, at a reasonable age -- so it can be assumed he made it about ~500 years ago. But I seem to recall the book saying that Dumbledore helped him make it. So either Dumbledore used the stone as well (unlikely it seems) or Flamel had already artificially extended his life, or Dumbledore is somehow hundreds of years old.  Am I remembering this incorrectly?  Thank you!


As the title says, I'm looking for an induction example, where the inductive step is rather simple to prove, but it's hard to find a base case for which the theorem holds.

According to :     ...proofs by mathematical induction   have two parts: the "base case" that   shows that the theorem is true for a   particular initial value such as n = 0   or n = 1 and then an inductive step   that shows that if the theorem is true   for a certain value of n, it is also   true for the value n + 1. The base   case is often trivial and is   identified as such, although there are   cases where the base case is difficult   but the inductive step is trivial.   What are some examples of proofs by induction where the base case is difficult but the inductive step is trivial?


I have the following go program that runs with:   ./hack/go/bin/wego   How can I create a symlink to run this program with the command weather?

I am installing p4v in /opt, but /usr/bin is on my path.  Is it possible to create a soft or symbolic link for p4v from /opt to /usr/bin, so I can just type "p4v" since /usr/bin is in my path?


My laptop is ASUS K 551 LB, which has an internal battery.  Would the battery's service life be longer leaving the laptop plugged in whenever possible, or running off the battery to regularly run down the charge?

Basically, I'm looking for some do's and don'ts. Is it bad to keep my laptop plugged in when I'm not using it (majority of the time)? Is it bad to plug it in once I've finished using it (with it having something like 30% or 70% life left)?     This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.


I'm sorry in advance if this is not the right place, but I don't know where else to post this.  I have four PS4 controllers and I haven't used two of them for at least 6 months...last night I charged them, and nothing happened.  When I plug them (into my PS4 with a USB cable) I get this yellow blinking light and after a while, it stops. When I press the ps button to turn them on I get a blue blinking light that eventually turns off...and again nothing happens.  Things I have tried without any luck:   Different USB cables (about 3 cables). Factory resetting my controllers (sticking a clip in the back of the controller for 10 seconds). Also restarted the controller by pressing the share button for 3 seconds, then holding the ps button for 5 seconds. Torn one of the controllers apart, disconnected the battery for about 4 hours, put everything back, same. Unplugged my PS4 from the power supply for 2 hours.   My PS4 won't detect those two controllers, they don't appear under the Bluetooth settings, this is really really weird.  I don't know what to do, does anyone knows something about this issue?

I was playing my PS4 two days ago and then packed it up with two controllers that were both connected to this PS4.   I got to where I was going, set everything up and now the controllers won't connect. They show pulsing orange when they plug in, but when I hit the PS Button to connect, it blinks white 1-2 times and goes back to orange.   I have tried resetting them both.  Can anyone help?


I have a question that I believe is related to @PetTaxi's question here: , but I didn't want to hi-jack it.    My issue is this.  I'm assuming the most distant objects in the observable universe are 46 B light years away.  A photo from one of these galaxies has been traveling 13.7B years.  I assume the galaxy that emitted the photon was 13.7B light years away at the time the photon was emitted.  So, the problem for me is, the galaxy is now 46B light years away which implies in my mind that the galaxy moved 32.3 B light years (the difference in where it was versus where it is now) in only 13.7B years.  But of course, that can't be true because it would mean faster than light travel.   So, how does a galaxy get that far away in such a short time?  There is likely something fundamental here I don't understand about how the universe is expanding....

We know that some galaxies are moving away from us faster than the speed of light and we know it by measuring the redshift, but how's that possible? If they're moving away say at $2c$, how would the light of the galaxy even reach us? How do we measure "redshift" for something faster than light?


i want to hide my layout which is in activity class and its visibilty handle in fragmetn class below is my code  Myfragment.java  Tags.mStringVarientSoldOut="yes"; ActivityDetailTest site = new ActivityDetailTest(); site.isSoldOut();   ActivityDetailTest.java  mLinearLayoutBottom is already declared in my onCreate() method of activity class  public void isSoldOut() {       if (Tags.mStringVarientSoldOut.equalsIgnoreCase("yes"))     {         mLinearLayoutBottom.setVisibility(View.GONE);     }     else     {         mLinearLayoutBottom.setVisibility(View.VISIBLE);     } }   when I run above code i m getting nullpointer error at line             mLinearLayoutBottom.setVisibility(View.GONE); any idea how can i solve this? your all suggestions are appreciable

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


My understanding is that light does not experience time. In attempting to understand what the universe would be like from the perspective of a photon, the answer I get is that the universe would be essentially 'frozen'. Answers I've seen describe the photon in a universe where it can move through space, but with events around it not moving at all in time.  So...from my frame of reference, it takes about 4 hours for light to go from Neptune to where I am on Earth. Conceivably I could move somewhere during that time to dodge the photons. But if from the photons perspective I don't have time to move out of the way, then there is a paradox of sorts.  Therefore I must be missing something here. Can someone explain how the motion of other things is possible from the perspective of a photon?

I read with interest about Einstein's Theory of Relativity and his proposition about the speed of light being the universal speed limit.    So, if I were to travel in a spacecraft at (practically) the speed of light, would I freeze and stop moving?  Would the universe around me freeze and stop moving?  Who would the time stop for?


My sister-in-law's parents arrived from China on tourist visa last December.  Due to worldwide concerns about the coronavirus, she filed i539 to extend their stay by 6 months.  The application is still pending, and it will probably be a while before they get to it.  Because she is still concerned about them traveling during this pandemic, she wants to know if it's feasible to apply for another 6 month extension while the current one is still pending. Also, do they have any other options in the current situation?  Under the current circumstances, would it be possible to apply for green cards for them, without them having to go back to their home country, if she sponsors them?

Given the current covid-19 situation where the home country (India) has stopped all international flights, how can one (65+ year old) extend their B2 visa or stay after I-94 extension? Any help is appreciated.  I called up USCIS regarding the same and they told me it usually takes around 6 months to process these applications. My main concern is what if the application is rejected and the applicant has already overstayed their original VISA expiry date, will it be considered illegal? What happens if it is considered illegal?  The BringIndiaHome Initiative, is an initiative by Indian and American Indian lawyers to assist stranded Indian citizens to return to India. The petition seeks the relief of directing the Government to formulate a scheme to identify Indian Nationals in distress in the US and airlift them, specially in view of the WHO travel advisory which advised nation States not to impose disproportionate and excessive travel bans.If anyone interested please mail :  or fill up this form :   P.S. Please don't remove the Airlift details I have added here, last time someone edited my posting and removed those details.It's an important info, don't delete it.


I got my Hungarian Student visa.  Initially, it is limited to 30days until I pick up my residence card. On the visa it states: Valid for: Hungary Single entry Validity: 30 days.  They mentioned in the embassy that I shouldn't leave Hungary until I got my residence permit card.  Can I land in Germany, since I can't get any direct flights to Budapest?

I am an Indian national. Right now I am staying in Israel. I will be moving to Germany on the last week of this month with german national visa directly from tel aviv. Ticket price of direct flight is high. So I am thinking to buy either Air France or LOT for travelling having layover at Paris or Poland. Am I allowed to do that? I mean is it mandatory to enter in Germany first? May I travel with these airlines with proper transit visa?


I am trying to build a customized Ubuntu based Live CD. My purpose it to have Ubuntu based installable ISO within minimum required packages including GUI plus additional VLC, and PDF reader packages in it.  After searching the web I found following 2 ways to prepare Ubuntu 12.04 Live CD,       I could have been able to create Live CD from both of the above options. But I am facing some problem in both option to achieve my purpose:   Following the first link, everything was fine except the installer, which is text-based instead of graphical. I was unable to add grub2, plymouth-x11 and ubiquity-frontend-gtk. Following the second link I wasn't able to remove unneeded packages.   What should I do?

I would like to customize Ubuntu live CD by installing some additional packages. I have followed   but it doesn't seems to work. Can anyone provide clear instructions?   Note: I do not prefer Remastersys, manual way will be appreciated.  Customization  Packages that I want to install:   Thunderbird    Samba    SSH       Changes that I need:   Remove Games menu from the Application menu Firefox shortcut on Desktop Radiance as the default Theme Different default Ubuntu Wallpaper   Configuration file changes   I want the panel to be placed at the bottom I want to paste my Samba configuration file instead of default Samba configuration I have few Firefox shortcuts and folders I would like to show that in Desktop Also it will be nice if you say me how to change the icon sets   Recent Updates   I have customized Ubuntu 10.10 with Firefox shortcuts and few folders on desktops. Everything went smooth. But the installer gets crashes after choosing the timezone. How do i fix this issue? Also setting wallpaper affects the login screen. The wallpaper which i set is displayed on the login screen also. I just want the default one for the login screen.


I don't know yet what database I'll use in the future - MySql, Postgresql, Sqlite3 or anything else. At the moment I'm using a database N.  What's more or less universal approach for storing latitude & longitude? Varchar? Or big integer? Or float?   Should I store them in 2 columns or one?

I see that the Point type is made to store geometric coordinates, however I don't see what problem it is trying to solve, or what advantages it offers over simply using two numerical columns. It's 16 bytes, so is it just an abstraction for two 8 byte floats? Or is it a string containing some kind of geohash that optimizes the performance of certain queries?  Let's say I want to get all the points for a specific viewport on a Leaflet map... with numerical columns representing latitude and longitude, I'd just filter for all the rows that have a latitude number between the N/S bounds and a longitude number between the E/W bounds, easy. I looked into using Point here, but the syntax is cumbersome and it seems to me like unnecessary overhead for development and for database performance... is it?


Give an example of a non-abelian group, in which $(ab)^3=a^3b^3$ for every element $a,b$ in $G$.  I understand that such a group should be of order divisible by 3 (see ). Also, it is easily seen that $(ab)^3=a^3b^3 \iff (ba)^2=a^2b^2$. But I can't come up with one single example.

I know that any group satisfying $x^2=1$ for all $x$ is abelian. Is the same true if $x^3=1$? I don't think it is, but I can't find a basic counterexample.


When I start wireshark this is the message I get.     Couldn't run /usr/bin/dumpcap in child process: Permission denied      Error by extcap pipe:   ** (process:4740): WARNING **: Option '--remote-filter' requires an argument      ** (process:4740): WARNING **: Missing parameter: --remote-host"

I used to run wireshark on ubuntu 17.04 with  ~/$ sudo wireshark   but now (just after update to 17.10) when I write the same I get an error  ~/$ sudo wireshark      QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'     Invalid MIT-MAGIC-COOKIE-1 keyQXcbConnection: Could not connect to display :0


I am trying to summon a villager that will trade custom player heads in 1.15.2.  Here is the code I have found to summon a villager trading a mob head:  /summon villager ~ ~1 ~ {VillagerData:{profession:farmer,level:5,type:plains},Offers:{Recipes:[{buy:{id:emerald,Count:1},sell:{id:dragon_head,Count:1},maxUses:1}]}}   Here is the code I have found to give myself a custom player head from FreshCoal.com, but it seems that something may be slightly off with this code. It works in a command block, but also triggers a warning:  /give @p player_head{display:{Name:"Strawberry Jam"},SkullOwner:{Id:"adc3ea73-5b42-4fea-a237-4a72b5",Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvYzBiOGI1ODg5ZWUxYzYzODhkYzZjMmM1ZGJkNzBiNjk4NGFlZmU1NDMxOWEwOTVlNjRkYjc2MzgwOTdiODIxIn19fQ=="}]}}}   Here is the code that I try for the custom villager, but it does not work:  /summon villager ~ ~1 ~ {VillagerData:{profession:farmer,level:5,type:plains},Offers:{Recipes:[{buy:{id:emerald,Count:1},sell:{id:player_head{display:{Name:"Strawberry Jam"},SkullOwner:{Id:"adc3ea73-5b42-4fea-a237-4a72b5",Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvYzBiOGI1ODg5ZWUxYzYzODhkYzZjMmM1ZGJkNzBiNjk4NGFlZmU1NDMxOWEwOTVlNjRkYjc2MzgwOTdiODIxIn19fQ=="}]}}},Count:1},maxUses:1}]}}   How can I change the code to make it work correctly? Right now, my villager trades only air.

I am making a Minecraft Mini Game adventure map, and one of the levels has a /setblock command, I am using the command in a way to spawn an item in a chest (Wooden Button) I need the wooden button to have CanPlaceOn tag so it can be placed on a log. I have tried this command: setblock 294 5 -1251 minecraft:chest 0 replace {Items:[{Count:1,Slot:0,id:minecraft:wooden_button,CanPlaceOn:[log]}]}`


I would like to disable the functionality of using Super+0...9 to open applications residing in the Dock, so that I can use Super+0...9 solely for switching workspaces.  From Ubuntu 17.10 up until, and including, Ubuntu 18.10, this could be disabled using:  gsettings set org.gnome.shell.extensions.dash-to-dock hot-keys false   (see )  After updating to Ubuntu 19.04, this solution does no longer work for me.  How can I achieve the same thing in Ubuntu 19.04?

I like to switch workspaces via Super+Number. But unfortunately the default behavior in Ubuntu for Super+Number is to select applications from the dock.   Is it possible to disable that functionality? I've tried overriding the keyboard shortcuts but it doesn't appear to be working.


Matter curves space time . as its mass grows the curvature of space-time grows. This curvature procedure of space time is to my opinion what slows down and prevents from mass to reach the speed of light. the bigger the mass the slower it goes with the same kinetic energy. Based on this logic ,since light always travels at the speed of light, I assume that it doesn't curve space time ( I am referring to photons travelling in open space time and not in a box where photons and matter interact).  since Gamma rays can produce matter and anti-matter pairs .Since I assume that photons do not curve space-time ,but matter does ,then in order to conserve the original photonic anti-gravitational behavior, its anti-matter pair should have neutralizing anti-gravitational behavior. So if matter "pulls" towards it and slows time ,anti-matter "pushes" away from it and makes time run faster .this can explain why we cant see anti matter ,since it is spread in space stretching it in contrast to the matters gravitational pull. this can also explain the source of the "dark energy" . This theory can be tested on anti-matter particles and photons in the future. what do you think?  I know that the question if photons apply gravity was asked before and that there is not enough data today to answer this question and we are all based on General Relativity equations. what I am asking is ,assuming that photons in free space do not apply gravity, can we predict based on the fact that a Gamma photon can generate matter and anti-matter pairs that anti-matter applies anti gravity in order to keep the neutralizing zero gravity of the photon? this in my opinion is not a duplicate question.

I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull on other objects? If so, does it depend on the frequency of the photon?


How don't wormholes violate the conservation of energy and momentum? Picture the following situation: a scientist creates a wormhole connecting the ceiling of a room with the floor. The two openings of the wormhole are vertically aligned, so if someone dropped an object in the entrance near the floor, it would "appear" instantly in the entrance near the ceiling and fall down to the floor because of gravity. And since both entrances are vertically aligned, the object would repeat the process, falling in the entrance near the floor and "appearing" near the ceiling again. This would create a loop that accelerates the object. Now imagine that the object is a magnet. If we constructed a coil around the falling object, we would basically create free infinite energy!!! Could this idea work? If not, why? And if yes, how is this even possible due to the law of conservation of energy?  Please help me not to freak out with this question in mind hahaha! Thank you!

Let's say I have a tube, of large radius (about 5 - 7 meters in diameter), with traversable wormholes at the ends. The wormholes are arranged as such that if something falls inside one hole from inside of the tube, it will come out at the other end still inside the tube. Now, let's say I empty all air from the tube (to make a "vacuum tube," if you will), set it upright and somehow manage to get a rock (or whatever other object) in there. My question now is, does the situation described above rule out the existence of traversable wormholes?  Or, if not, since the rock is falling through the wormhole over and over again, will it always be accelerating at the same rate? Or will its velocity only always be approaching light speed? In either case, would the rock's mass increase to the point that it overpowers Earth's gravity, or even collapses into a singularity? Or is there something that would prevent that from happening?


TLDR. is just the title.  I know nothing about photography, sorry. My dad has a d90 he never uses, so I use it to take photos when I need them for something.  Anyways, I put it on raw mode. when I open the photos on my computer, the jpg looks like the viewfinder view. The NEF looks like the jpg for a second, then gets "rendered..?" with boosted highlights so it looks washed out. This is actually what the playback looks like on the low resolution camera display.  Im probably doing the settings wrong, but I cant explain why the jpg looks normal.

Everybody who is using Lightroom probably has seen this. After importing RAW files, Lightroom shows a preview, but contrast and color of the preview change after a few short seconds to a slightly different view.  For some users the change is small, for others the change is huge. Colors are different (read: wrong), contrast is off.  Rumor says this is happening only (more?) for Nikon users.  What is Lightroom doing here?  I'd guess that for the first preview, LR is showing the JPG preview file, which is embedded in the RAW file. Then after a moment, LR renders the RAW file itself to show it's own interpretation.  But why is this interpretation so different from the embedded JPG?


I'm attempting to retrieve the ID of the element I'm clicking on  $mainBox.on('click', '.menuBtn', function(event) {     console.log(event.target.attr('id'))     });   the element I'm clicking is loaded as part of an external html, this would be the line that is being clicked:
03Menu Item
   how do I get item03? event.target.attr('id') doesn't do it

Is there any way to get the ID of the element that fires an event?  I'm thinking something like:    $(document).ready(function() {   $("a").click(function() {     var test = caller.id;     alert(test.val());   }); }); <script type="text/javascript" src="starterkit/jquery.js"></script>  <form class="item" id="aaa">   <input class="title"></input> </form> <form class="item" id="bbb">   <input class="title"></input> </form>     Except of course that the var test should contain the id "aaa", if the event is fired from the first form, and "bbb", if the event is fired from the second form.


I have a the following code  StringToSearchIn ="Hello word (Figure 1)";  patternString= "word (Figure 1)"  Pattern pattern = Pattern.compile(patternString);        Matcher matcher = pattern.matcher(StringToSearchIn); matcher.find()   This is returning 0, as '( or )' is not recognized, when I change to      patternString= "word \\(Figure 1\\)" , is returning the match counter as 1 Is there a way to change my patternString to search for '(' and replace with '\\(' dynamically before creating a pattern.   Thanks in advance.

Does Java have a built-in way to escape arbitrary text so that it can be included in a regular expression? For example, if my users enter "$5", I'd like to match that exactly rather than a "5" after the end of input.


For each positive integer $n$ let $f_n : [0,1] \to R$ be a continuous function, differentiable on   $(0,1]$, such that   $$|f_n^{~'} (x)| \leq\frac{1 + |\ln x|}{\sqrt{x}} $$for $0 < x \leq 1$.   and such that   $$−10 \leq \int^1_0 f_n (x)~\mathrm{d}x \leq 10.$$   Prove that $\{f_n \}$ has a uniformly convergent subsequence on $[0,1]$.     I try to use the Arzelà–Ascoli theorem, which requires me to prove $\{f_n\}$ is uniformly bounded and equicontinuous.   From the second inequality, we conclude $\{f_n\}$ is uniformly bounded.   However, I stuck with proving they are equicontinuous.   I try to use the Lagrange theorem so that it suffices to show the $\{f_n^{~'}\}$ is uniformly bounded.   However, the first inequality cannot give us what we want since the function on the right side is not bounded on $(0,1]$. So what should I do?

This is almost surely an Arzela-Ascoli question, since it comes from an old exam of which such problems are quite common. Unfortunately, I can't seem to get it though.  $\{ f_n \}$ is a sequence of functions $[0,1] \to \mathbb{R}$ satisfying $|f_n'(x)| \leq \frac{1 + |\ln (x)|}{\sqrt{x}}$ and $-10 \leq \int_0^1 f_n(x) dx \leq 10$ for every $n$. The question is to show the existence of a uniformly convergent subsequence.  In these kinds of situations, the bounds given usually turn into something nice  to force uniform boundedness. Maybe I could hope to establish equicontinuity using the integral somehow, but I'm not told that the $f_n$ are always positive, so the absolute values would probably screw things up anyway.  Is it an easy problem I'm missing or is this totally the wrong track? If so, what's the right track?


I am trying to print the current line number(line number of ide) of a certain code from intellij. How do I do that?  1 System.out.print(getCurrentLineNo());//sample code 2 System.out.print(getCurrentLineNo());//sample code 3 System.out.print(getCurrentLineNo());//sample code 4 System.out.print(getCurrentLineNo());//sample code

How to print line numbers to the log. Say when outputting some information to the log, I also want to print the line number where that output is in the source code. As we can see in the stack trace, it displays the line number where the exception has occurred. Stack trace is available on the exception object.  Other alternative could be like manually including the line number when printing to the log. Is there any other way?


I have a face appearing in object mode which is not present in edit mode. Does anyone know why or what to do to remove it?  The screenshots show the problem clearly:  Edit mode showing no face:   Object mode showing a face:   Thanks, Andrew

I have append a mesh (rex) from this .blend .  In edit Mode I see different vertices from objcet mode (see pictures). The vertices of belt are missing!  OBJECT MODE:   EDIT MODE:   How can I edit vertices of belt? Is It a bug?  This is my .blend  maybe can help.


I'm a complete newbie, so please be easy on me! I'm trying to stack to images on top of eachother, one image centered, the other slightly off-centered. I also want this to be responsive. Here's how far I got for my HTML:

  CSS: .img-wrap{   position: relative;   height: 500px; }  .nijntje {   width: 500px;   position: absolute; }  .nijntje-bg {   position: absolute;   width: 420px;   z-index: -1; }  Added the height to the img-wrap to push down text below. Not sure if this is the most elegant solution. But the real problem: my images aren't centered yet, and I can't figure out how to get them centered (and the bg image slightly off-centered). Would love your help, thanks!

I want to overlay one image with another using CSS. An example of this is the first image (the background if you like) will be a thumbnail link of a product, with the link opening a lightbox / popup showing a larger version of the image.   On top of this linked image I would like an image of a magnifying glass, to show people that the image can be clicked to enlarge it (apparently this isn't obvious without the magnifying glass).


I interested in this question. how many numbers meet this condition? I think a few of them meet this but I want a proof for this. also I'm not very pro in mathematics.

I've done the base step, but how do I prove it is true for $n+1$ without using a fallacy? $$4(n!)>2^{n+2}\quad \text{for } n\geq 4$$ Please help.


For $a \neq 1$ and $n>0$, $(1-a^{n+1})/(1-a)=1+a+a^2+...+a^n$  How do you prove this by induction?

$$\sum_{k=0}^nq^k = \frac{1-q^{n+1}}{1-q}$$  I want to prove this by induction. Here's what I have.  $$\frac{1-q^{n+1}}{1-q} + q^{n+1} = \frac{1-q^{n+1}+q^{n+1}(1-q)}{1-q}$$  I wanted to factor a $q^{n+1}$ out of the second expression but that 1- is screwing it up...


The popup above is a result of trying to downvote as a user with less than 125 reputation. The popup, in case you can't see it, states the following (emphasis mine):     Thanks for the feedback! Votes cast by those with less than 125 reputation are recorded, but do not change the publicly displayed post score.   How are these downvotes recorded, and what do they do? Or rather, do they do anything at all?  The popup included is from trying to downvote a post on the  site with only the Association Bonus.

I've just noticed that if you try to vote without having a privilege to vote, you're greeted with such message:        So, that's interesting. Does it mean that if I gain 125 (or 15, in case I'm upvoting not having 15 reps) rep on that site, my "suggested" vote goes public and until then it would be recorded as it's done with anon feedback?  And until this change, the votes weren't recorded as anonymous, or has the new message saying that it acts as feedback been added just to not upset users?


The output of the free command that I fired on my linux host is as belows:  free               total        used        free      shared  buff/cache   available Mem:      263846320    47746620     3290072     1140808   212809628   214382420 Swap:             0           0           0   I am not able to figure out what this available part is specifying. The free memory is very less shown i.e around 1.24% even though the total memory is way high and used memory is around 18.09% only.  free -h               total        used        free      shared  buff/cache   available Mem:           251G         45G        3.1G        1.1G        202G        204G Swap:            0B          0B          0B   Does it mean I wont be able to start more applications as free memory is very less. The used memory is 18% only. So shouldn't free memory be 72% and not 1.24% as the command is showing above.  I am confused. Can anyone help?

I would appreciate help in interpreting the output of 'free -m' below.    -bash-4.2$ free -m               total        used        free      shared  buff/cache   available Mem:          15793        7112          88        7840        8591         611 Swap:         16891        5289       11602    If I have nearly 11GB free then why am I seeing swap usage.  Shouldn't that be 0?   Also, the 'shared' value is 7840.  Is this memory available for a new application? Is only 'cache' memory available for new applications?  In other words, 'shared' and 'buffer' memory are not available for new applications? How should I interpret the 'available' column with a value of 611?  How is this value arrived at?


I want to make below table using latex. But I don't know how to combine \multirow and \multicolumn. How can I make below table using latex?  Thank you very much.

Here is a simple table.  I want to merge 4 cells. I want to combine the three "this" cells area in this table. I thought I have to use multirow and multicolum at same time. However, I could not find how to use it.  If possible, could you post the modified LaTeX source code?     My LaTeX code:  \documentclass{article} \usepackage{multirow}% http://ctan.org/pkg/multirow \usepackage{hhline}% http://ctan.org/pkg/hhline \begin{document}  \begin{table}[ph] \begin{center} \begin{tabular}{c|c|c|c|c} \hline \multirow{2}{*}{Raaa (k)} & \multicolumn{4}{c}{C ()} \\ \hhline{~----}  & 3.3 & 2.5 & 1 & 0.5 \\ \hline \multirow{2}{*}{Raaa (k)} & \multirow{2}{*}{this} & this & 0.5 & 0.6\\ \hhline{~~~--}            &                       & this & 0.7 & 1.2 \\ \hline \end{tabular} \caption{R, C ripple size} \label{T:peak} \end{center} \end{table} \end{document}


I want to play Minecraft but I have one controller only. I do have a PC as well. Can I play PC and PS4 Minecraft?

My kids are playing Minecraft on 2 PCs, creative mode.  They are connected by the way of one of them starts a single player game on the other one than joins that game over the LAN.  Can I, using Minecraft PE on my iPad, join their game as well?


Just installed Ubuntu 16.10, and now I am in the login loop. I can use ctrl alt f3 to open the console, but dunno what kind of command would fix this. Can you please help me?

My Ubuntu is stuck in a login loop when trying to enter my desktop. When I login, the screen gets black and soon after that the login screen comes back.   I've read that the problem might be caused by an error depending on the graphics, here's my graphics card: ATI Radeon 7670M


I stupidly deleted the system python on High Sierra, hoping to only use the Homebrew version. However, now I want it back. How can I restore it?

I've deleted a system file from my Mac and need to get it back.  System files can include:   hidden files in the root of / - especially unix files in /private  /System files /Library files /Applications files that ship with the core OS   System files are not any app, user files or files that can be regenerated by a known sequence such as cache files, Spotlight index files, etc…    Canonical question and answer for .


I am trying to install Ubuntu 18, but in the part of installing Ubuntu I get this error  ima: Error Communicating to TPM chip  In the image I show the BIOS settings that I have and the error:

I am getting the following error message as a list of 4 or 5 lines with differing numbers at the beginning of each line during boot for a long while:  ima: error communicating to tpm chip   I am using Ubuntu 19.04 (though this error was existing for a while at the older versions) and my computer is a Toshiba Z930.


I want to program at89c2051 chip. I am referring circuit diagram where the optocoupler is used to handle the 2 voltage levels (+12V and +5V). i didn't understand how Pin A0 and A1 will control the voltage level. Here is the optocoupler circuit

I am having trouble understanding the following portion of schematic from AT89C2051 programmer circuit. Please help me comprehend what is going on here.   Here is what I understand:   A1 directly controls the 12V going to AT89_RST pin When A1 is low,    If A0 is high, AT89_RST pin sees high. if A0 is low, AT89_RST pin sees low.    So why is the 5V added there with the diode? I suspect it might be one of the following two reasons, but I really don't understand why.   To pull up AT89_RST to 5V. But A0 can be driven both high and low. Why pull it up? As some form of protection to prevent A0 from getting roasted with 12V? I think it might be the case, but I don't understand how it works to prevent that.   Notes:   AT89C2051 Programmer's . A0 and A1 are being driven by arduino (5V logic).


I have 2 strings that have a 0 and a 16,63 as follows:  var diferencia = "0"; var estalviPotencia = "16,63";   If I put an alert to see its value with two decimals I obtain:  alert(parseFloat(diferencia).toFixed(2)) -- returns 0,00 alert(parseFloat(estalviPotencia).toFixed(2)) -- returns 16,63   But if I actually sum them and then get the value I get:  alert((parseFloat(diferencia) + parseFloat(estalviPotencia)).toFixed(2)); -- returns 16,00   I can't see the error and why I am obtaining that number...  Edit por possible duplicate:  I am NOT saying that the decimals are wrong as said on that answer (which asks why there so MANY decimals but why I am NOT obtaining any decimals at all.

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


I am currently studying Gauss Law and Electric flux , during one of my exercises they ask me to find the electric flux of a sphere with radius  5 cm and my  point charge is 10 cm to the left of the center of this sphere. Why is it that the electric flux is 0 if the  Electric field is not 0?

Why is  due to external charge i.e a charge outside a closed surface equal to 0?  P.S:Moreover I found this statement confusing:-  Electric field appearing in the Gauss' law is the resultant electric field due to all the charges present inside as well as outside but the contribution of outside charges in producing flux is zero. Can someone help me understand it.


I have a server that needs to accept incoming ssh connections with portforwarding. The incoming clients request a port forward from a port on the server to a port locally. They authenticate using a public/private key. So: on the client end -R 40001:localhost:8443 is used to enable the server to connect to its own port 40001 and access an application on the client's port 8443.   How do I restrict the server so that this specific user can only forward port 40001 and no other port? I've looked at permitopen, but it seems to work only for forward, not reverse tunnels.

We have a public server which accepts SSH connections from multiple clients behind firewalls.   Each of these clients create a Reverse SSH tunnel by using the ssh -R command from their web servers at port 80 to our public server.  The destination port(at the client side) of the Reverse SSH Tunnel is 80 and the source port(at public server side) depends on the user. We are planning on maintaining a map of port addresses for each user.  For example, client A would tunnel their web server at port 80 to our port 8000; client B from 80 to 8001; client C from 80 to 8002.  Client A: ssh -R 8000:internal.webserver:80 clienta@publicserver  Client B: ssh -R 8001:internal.webserver:80 clientb@publicserver  Client C: ssh -R 8002:internal.webserver:80 clientc@publicserver   Basically, what we are trying to do is bind each user with a port and not allow them to tunnel to any other ports.   If we were using the forward tunneling feature of SSH with ssh -L, we could permit which port to be tunneled by using the permitopen=host:port configuration. However, there is no equivalent for reverse SSH tunnel.  Is there a way of restricting reverse tunneling ports per user?


I've created a settings page for my theme, and I'd like to be able to set the frontpage from there, but I don't know how I can change the frontpage in code?  This is the setting:  $node_type = "page"; $result = db_query(     'SELECT n.nid, n.title FROM {node} n WHERE n.type = :type',     array(':type' => $node_type) ); $options = array(); foreach ($result as $record) {     $options[$record->nid] = $record->title; }  $form['static_nodes']['front_page_id'] = array(     '#type'        => 'select',     '#title'       => t('Frontpage'),     '#options'     => $options,     '#description' => t('Set the page used as the frontpage.'),     '#default_value' => theme_get_setting('front_page_id'), );

I want to set the Drupal front page programmatically at run time. How can I do this? Is this possible?