[I apologize if it has been asked, I think it must have been but I couldn't find a similar question.]  I often receive invitations / calls for papers to write papers in journals. 95% of these cases are obvious spam publications, but in about 5% I see a letter that's not entirely generic, e.g. they mention my previous publications in the subject** and they write something that appears genuine about the publication. They also write the name of the editor in chief.   My question is how to assess this new journal's quality? I mean, nice journal pop up once in a while and just because it's a new journal, does not mean it's necessarily "fake news".   Here are a few points I thought about:   Wait a few months/years until I see reputable people publish in it, but then I will have missed my shot, possibly. Inspect the editor's reputation. If she/he appears reputable (e.g. have published in journals I know to be good), then the journal is okay. Inspect the publisher's "parents", for example if it's ACM, Springer, IEEE, etc., then maybe it's worthwhile (but then, I can't say definitively either way).   I would appreciate any points on the subject.  ** yes, these messages can nevertheless be generated automatically.

A colleague and I recently submitted a paper to a journal with an impressive-sounding name, the "International Journal of Artificial Intelligence and Computational Research". According to ,      IJAICR is a referred [sic] journal in the field of computer science, artificial intelligence and soft computing methods.   It was accepted two days after we submitted it. That's too fast. We were suspicious. Although the journal said that all papers are peer-reviewed, we could not see how that was done in two days. Plus, we received no comments from the reviewers. Also, the submission guidelines didn't ask for a "blind" copy (without our names or any references to who we were).   But wait, there's more.  The acceptance letter asked us to send them US$300 to publish it. We did not. We've withdrawn our submission and will submit a new version of the paper to a more reputable journal in the coming months.  How might we make a better choice of respectable journals before we submit next time?


Which of the following is correct?  If Insurance company or Law Firm have changed their opinion then please let us know.  or  If Insurance Company or Law Firm has changed its opinion then please let us know.

We always get work done, regardless of what mood Bill or I is/am/are in.   Which form of 'be' would be used here?


I want to sum a series of integers, say from 1 to 5, but I want to generalise this function. I have seen that the function is:  $$ \text{sum} = \frac{n(n+1)}{2} $$  where $n$ is the number to sum up to  So for $n=5$, i.e. $1 + 2 + 3 + 4 + 5$, the sum is $15$.  My question is, how could I (without knowing by heart) work out that function myself?

Apparently $1+2+3+4+\ldots+n = \dfrac{n\times(n+1)}2$.  How? What's the proof? Or maybe it is self apparent just looking at the above?   PS: This problem is known as "The sum of the first $n$ positive integers".


We know that Men (including hobbits) are gifted Doom, and the Elves are gifted immortality, but what are the other gifts? What did Eru Ilúvatar give to the others?

Silmarillion tells us what happens to the souls of Men and Elves:     ... For the Elves die not till tile world dies, unless they are slain or waste in grief (and to both these seeming deaths they are subject); neither does age subdue their strength, unless one grow weary of ten thousand centuries; and dying they are gathered to the halls of Mandos in Valinor, whence they may in time return. But the sons of Men die indeed, and leave the world; wherefore they are called the Guests, or the Strangers. Death is their fate, the gift of Ilúvatar, which as Time wears even the Powers shall envy. ...   But what happens to the souls of other creatures likes dwarves, hobbits, ents, orcs, uruk-hai, maiar, balrogs (and other conscious creatures I might have forgotten)?


Using approximation with a spreadsheet, I see that:  $$\sum_{n=1}^\infty \frac{1}{n\ 2^n} = \ln 2$$  Is there a proof of this?

Problem:  Show that $$\ln2 = \sum_\limits{n=1}^\infty\frac1{n2^n}.$$  My progress:  The problem before this one had me find the Taylor series for $\ln(1-x)$ which was $$-\sum\limits_{n=1}^\infty \frac{x^n}n$$  so I figured I'd use $x=-1$ and plug that into the Taylor series. However, there was a side note stating that the Taylor series I found is only valid for $x\in(-1, 1)$. And in any case, my calculation isn't going anywhere, since I end up with the series $1-\frac12+\frac13-\frac14\cdots$  Question 1: How can I use this to solve the problem stated initially, and in the title?  Question 2: I can see why $x$ is restricted to be less than 1, to prevent taking the log of zero or a negative. Why is it not valid for x greater than 1?


I want to use a function with a parameter, but it somehow doesn't work. Can you tell where is the problem? If I leave empty the parameter list, and in the if condition I put a number instead of "num", then the function works. let lpFunctionPress = function (num) {     if ($(this).val().length >= num) {        $(this).parents('.license-plate-container').children('.error-message-license-plate').hide();        $(this).css('border-color', '#CDD0D2');     } else {        $(this).parents('.license-plate-container').children('.error-message-license-plate').show();        $(this).css('border-color', '#fe0000');        } } licensePlate1.on('input', lpFunctionPress(2));

The situation is somewhat like-  var someVar = some_other_function(); someObj.addEventListener("click", function(){     some_function(someVar); }, false);   The problem is that the value of someVar is not visible inside the listener function of the addEventListener, where it is probably being treated as a new variable.


I'm seeing an odd issue in my code  In my mfc/c++ application, there is a function that gets called at 2 different points. Once, when a dialog/component is displayed. The second time is when some generation is happening from a 2nd dialog/component. The only difference is that from the 2nd dialog, the call is happening in a new thread.  Within this function, broken down to its simplest, 2 doubles are subtracted.  double a = -13.497999999999999 double b = 33.564999999999998  a - b   when I step through the code, I am getting different results from the subtraction and is having a knock on affect to other calculations. The result from Dialog 2 seems to be closer to what is valid.  Dialog 1 - 20.066999435424805  Dialog 2 - 20.067000000000000   Very odd that simple subtraction would return different results. The differences may be minimal, but they do build up to cause a larger problem.  using VS2010, settings all correct as far as I can tell.  I've tried using floats and long double's to see if that would resolve anything but they don‘t.

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


I have Ubuntu 10.10 installed in my laptop. How can I upgrade it to the latest version without upgrading to 11.04? Also how much time will this take? I do not want to lose any data. I also have Windows 7 in my machine.

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


I need to serve about 50k users with environment of video streaming and other media like images, audio and browsing static pages html, css and js files so i will assume that all 50k will be streaming videos at same time to get max hardware needed

This is a  about capacity planning for web sites. Related:      What are some recommended tools and methods of capacity planning for web sites and web-applications? Please feel free to describe different tools and techniques for different web-servers, frameworks, etc., as well as best-practices that apply to web servers in general.


Hello, Maybe this question is repeated, but I didn't get the right answer for it. In my situation, I have 2 SSDs drives C: and D: In C: I have Windows 10 installed. In D: I have some data ( I will move them and keep this drive with no data) --- The question is : Can I install Ubuntu 20.04 in D: drive ? and how I can make it the dual-boot (with Windows 10) ?, Is there any issue with that?. **BTW , I have UEFI BIOS.**  Thank you :)

I have gotten as far as to create the bootable usb, booting into that bootable usb and getting to the install options however i quit because I had some concerns.  I currently have a Samsung 850 evo 1tb that has win 10ninstalled. I want to dual boot with Ubuntu 18.04 by installing it on a brand new unformatted uninitialized Samsung 860bevo 250gb. Should i format the brand new ssd as a new volume in win 10 and then proceed with the Ubuntu install on this volume. What else should i do? Im a first time Ubuntu user and installer.  Any and all help is appreciated.


In my attempt to run VirtualBox in Debian 8 I got:  alex@server-2:~$ virtualbox WARNING: The vboxdrv kernel module is not loaded. Either there is no module          available for the current kernel (2.6.32-042stab126.1) or it failed to          load. Please recompile the kernel module and install it by             sudo /sbin/vboxconfig           You will not be able to start VMs until this problem is fixed. Qt FATAL: QXcbConnection: Could not connect to display Aborted   In my attempt to follow this suggestion I got:  alex@server-2:~$ sudo /sbin/vboxconfig [sudo] password for alex: vboxdrv.sh: Stopping VirtualBox services. vboxdrv.sh: Building VirtualBox kernel modules. This system is currently not set up to build kernel modules. Please install the Linux kernel "header" files matching the current kernel for adding new hardware support to the system. This system is currently not set up to build kernel modules. Please install the Linux kernel "header" files matching the current kernel for adding new hardware support to the system.  There were problems setting up VirtualBox.  To re-start the set-up process, run   /sbin/vboxconfig as root.   My kernel version:  alex@server-2:~$ uname -r 2.6.32-042stab126.1   My linux-headers:  alex@server-2:~$ dpkg --get-selections | grep linux-headers linux-headers-3.16.0-4-amd64                    install linux-headers-3.16.0-4-common                   install linux-headers-amd64                             install   In my attempt to get right linux-header I got:  alex@server-2:~$ sudo apt-get install linux-headers-$(uname -r) Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package linux-headers-2.6.32-042stab126.1 E: Couldn't find any package by regex 'linux-headers-2.6.32-042stab126.1'   Then I tried to upgrade my linux kernel in order to be consistent with linux-headers  alex@server-2:~$ sudo apt-cache search linux-image linux-headers-3.16.0-4-amd64 - Header files for Linux 3.16.0-4-amd64 linux-image-3.16.0-4-amd64 - Linux 3.16 for 64-bit PCs linux-image-3.16.0-4-amd64-dbg - Debugging symbols for Linux 3.16.0-4-amd64 linux-image-amd64 - Linux for 64-bit PCs (meta-package) linux-image-amd64-dbg - Debugging symbols for Linux amd64 configuration (meta-package) nvidia-kernel-3.16.0-4-amd64 - NVIDIA binary kernel module for Linux 3.16.0-4-amd64  alex@server-2:~$ sudo apt-get install linux-image-3.16.0-4-amd64 Reading package lists... Done Building dependency tree Reading state information... Done linux-image-3.16.0-4-amd64 is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.   That seems that I have newest version. Now I have no clue what to do next in order to fix my problem with running VirtualBox. Do you have any suggestion?

I'm attempting to install VirtualBox inside of an offsite OpenVZ instance I got a good deal on. The point being to run a small Windows XP box for some kind of Windows Server.   Yes, it's an experiment. No, it's not for production.   It seems like everything would work fine, but the installer can't find my distro's sources. My instance has Debian 6 installed. Running uname -r gives me 2.6.32-042stab061.2. I've looked all through my apt-cache for anything similar, tried installing linux-sources-2.6.32 and a variety of linux-headers, but I'm having no luck.  Does anyone know how I can get the proper sources for this instance so VirtualBox can compile itself? Thanks.


I have a bunch of data that I fit a linear regression to, and now I need to find the variance of my slope. Is there an analytical way to get this?  If an example is necessary, consider this my data in R:  x <- c(1:6) y <- c(18, 14, 15, 12, 7, 6) lm(y ~ x)$coefficients   So I have a slope estimate of -2.4, but I want to know the variance of that estimate.  After looking at previous questions, I've seen a few equations for estimating the slope parameter, but I'm a little confused about what the differences between equations are and what approach is valid for my problem.  For example, the answers in  say that $\newcommand{\Var}{\rm Var}\newcommand{\slope}{\rm slope}\Var[\slope] = \frac{V[Y]}{\sum\left(\frac{x_i-\bar{x}}{\sum(x_i-\bar{x})^2}\right)}$.   says that $\Var[\slope] = \frac{V[Y]}{\sum(x_i-\bar{x})^2}$.  And if I look at the output in R (as a "check" mechanism), I'm given two other ways I could potentially calculate the slope variance (one using the standard error, another given the covariance matrix). I feel like I'm missing something key because all these estimates give me similar (but not the same) answer.

Can we say   $$\text{Var}(\beta_1) = \text{Var}\left(\frac{\sum (x_i-\bar x)y_i}{\sum (x_i- \bar x)^2}\right) = \left(\frac{\sum (x_i-\bar x)}{\sum (x_i- \bar x)^2}\right)^2 \text{Var}(y_i) \;\;??$$  I am not sure if I can separate the $x$'s i from $\sum (x_i-\bar x)y_i$. This expression seems like a linear combination of $y_i$'s. Is this legit because every $y_i$ follows the same distribution?


If I define $ I.J=\{ij : i \in I $ & $  j \in J \} $. Then prove that it is not necessrily an ideal, where $I,J$ are ideals in a ring $R$.  I have found one counter example in $R[x,y,z]$ for $I=<x,y>$ & $J=<x,z>$ & $R$ is commutative ring without unity.  But can anyone give me any other simple example. Roughly speaking observe what we have show that is $ i_1j_1 + i_2j_2 \neq i_0j_0 $.

If $U,V$ are ideals of a ring $R$, then which of the following is also an ideal of $R$?   $U+V=\{u+v\mid u\in U,v\in V\}$ $U\cdot V=\{u\cdot v\mid u\in U,v\in V\}$ $U\cap V$   My attempt: I have proved $U+V$ and $U\cap V$ are ideals of $R$.  My problem: I have problem about the second option. I think it is not ideal of $R$. If I am wrong then please prove this otherwise give one counter example to show that $U\cdot V$ is not ideal of $R$.


When I try to open another partition in my PC, it shows this error message:     How can I fix this error??  (Ubuntu 16.04)

Whenever I boot Ubuntu, I get a message that it cannot mount my windows partition, and I can choose to either wait, skip or manually mount.  When I try to enter my Windows partition through Nautilus I get a message saying that this partition is hibernated and that I need to enter the file system and properly close it, something I have done with no problem so I don't know why this happens.    Here's my partition table, if any more data is needed please let me know.     Device Boot      Start         End      Blocks   Id  System /dev/sda1            2048    20000767     9999360   83  Linux /dev/sda2        20002814   478001151   228999169    5  Extended /dev/sda3   *   478001152   622532607    72265728    7  HPFS/NTFS/exFAT /dev/sda4       622532608   625141759     1304576   82  Linux swap / Solaris /dev/sda5        20002816   478001151   228999168   83  Linux


I have an noteboook ASUS X200CA with Ubuntu 12.04 factory preinstalled.  I would like to update the operating system but I'm afraid it is not working properly, consume more resources than my computer can support or have problems with drivers.  Could someone tell me if the new Ubuntu on this computer working properly?  Thanks!

For a given hardware configuration, how do I find out if Ubuntu will run on it? What considerations should I take into account when choosing an Ubuntu version and  such as:    with a lighter desktop than the usual Gnome and Unity  with the even lighter LXDE desktop   Obviously Ubuntu does not run on some processor architectures. So how do I go about choosing the right version and derivate. How can I find out the minmal system requirements?


I have two device on my network LB (192.168.1.10) and RP1 (192.168.0.20) I am wanting all the MySQL stuff to be hosted on the LB and all the web stuff to be hosted on the RP1. I have installed mysql-server-5.5 on both devices. But when I perform the command: $con=mysqli_connect("192.168.1.10","foo","password","max");  On the web page I get the error:  Warning: mysqli_connect(): (HY000/2003): Can't connect to MySQL server on '192.168.1.10' (111) in /var/www/example.info/public_html/submit.php on line 6  And obviously when I try localhost (replacement for "192.168.1.10" in the snippet above) I get the error:  Warning: mysqli_connect(): (28000/1045): Access denied for user 'max'@'localhost' (using password: YES) in /var/www/example.info/public_html/submit.php on line 6   I have also tried: $mysql --host=192.168.1.10  On the RP1 and I get the error:  ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.1.10' (111)   What am I doing wrong?

I have an Ubuntu server and I've installed MySQL.  How would I use my two physical static IP addresses in my.cnf bind-address -- can I add two IP addresses?


I want to calculate the following sum: $$\sum_{m=1}^{\min\left\{M,n\right\}} \binom{N-M}{n-m}\binom{M}{m}.$$     Attempt: The above sum is a part of a bigger problem.  By rearranging the bigger problem, I found that instead of above sum I need to find an ``alternative'' sum which is    $$\sum_{m=1}^{\min\left\{M,n\right\}} \binom{N-n}{M-m}\binom{n}{m}.$$   I also found that such sums may be related to Gamma function, but I could not apply it here.

I am not able to show this case of Vandermonde's Convolution without using induction. Can someone help me?  $$ \binom{n}{m} = \sum_{k=0}^{m} \binom{n-p}{m-k} \binom{p}{k}. $$  I thank now.


The Electric field lines coming out of a charge are infinite, So the lines passing through a closed surface should be infinite , right?

I've already went through . Yet, I still can't understand the meaning of "density" of electric field lines whose number is, in reality, infinite.  One of the answers , for instance, states that the ratio of two densities is independent of the number of field lines, so even when their number is infinite, they would always end up canceling each other when computing the ratio of two densities ( for the field lines generated by a point charge), the mathematical  proof of this statement makes sense. However, in reality, the number of field lines is infinite, and field lines don't cancel each other, so even if we get further from our point charge, the number of field lines per unit area would still be infinite, no matter how far or near we're from the source.   Am I missing something?


I want to check if my string contains all the upper case value or not for that I am using the below code but It does not work as expected for case 1 and only work for case2.  Case 1   string myString = "SWEET POTATO"; myString.All(char.IsUpper)   Case 2  string eval = "POTATO";   eval.All(char.IsUpper)   It does not give me any error but I want in both the cases it will return true because in both the cases string value is in Upper case letter

In C# is there a way to detect if a string is all caps?  Most of the strings will be short(ie under 100 characters)


Could we feel a jetlag-equivalent effect when we travel a long distance in the North-South direction? We would be moving from summer to winter in one day. Doesn't this affect our biological clocks?

Changing longitude affects sleeping - that's called jet-lag.  But does changing latitude affect sleeping? For example, does flying from Sydney to Tokyo, when the former is in winter, and the latter is in summer, have any affect on sleeping? If so, is there a term for it?


Good day people. I am working on a java-ee project, specifically working on exporting a datable to spreadhseet(xls). I have a method called postProcessXLS. I use this method to auto adjust the column width of the generated spreadsheet and also to add cell styles and formatting. When i run the app, the method postProcessXLS throws a null pointer exception without referencing the line.  bean   public void postProcessXLS(Object document) throws IOException,     BadElementException, DocumentException {     try {         HSSFWorkbook wb = (HSSFWorkbook)document;         HSSFSheet sheet = wb.getSheetAt(0);         HSSFRow header = sheet.getRow(0);          HSSFCellStyle cellStyle = wb.createCellStyle();         cellStyle.setFillForegroundColor(HSSFColor.GREEN.index);         cellStyle.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND);          for (int i = 0; i < header.getPhysicalNumberOfCells(); i++) {             HSSFCell cell = header.getCell(i);              cell.setCellStyle(cellStyle);         }          for (int colNum = 0; colNum < header.getLastCellNum(); colNum++) {             sheet.autoSizeColumn(colNum);         }     } catch (Exception ex) {         LOG.error("Could not process spreadsheet" + ex);     } }

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?


Are magical items such as:  Staff of Frost DMG page 202 Staff of Power DMG page 202 Wand of Fireballs DMG page 210 Wand of the War Mage +1 DMG page 212  Considered to be foci usable for spellcasting, such as:  Staff PHB, page 151 Wand PHB, page 151

The various magic rods, wands, staves, etc. in the DMG all have certain abilities. But do they also count as arcane foci for the purpose of not needing material components for all your other spells?


Please tell me, with all the freehand circles and illustrative figures you can muster, how one goes about posting a screenshot in a question on Stack Overflow?

Sometimes I need to upload, embed, or display inline an image in a question or answer. How can I do that?


I have two DataTables DT1 y DT2. DT1 has two rows and DT2 has three rows. In both DataTables row1 and row 2 have the same columns and values. But row3 not exist in the DT1, it will be my result.  DT1: row1, row2  DT2: row1, row2, row3     Res: DT3: row3

Is there a relatively straightforward way to get the intersection of two DataTables in .NET?  I can think of the obvious ways (iterating over both tables myself in O(n^2)), but I'd like something a little more elegant if it's available.  I suspect there may be an intelligent way that I'm not seeing.  Readability and maintainability are important, of course, so I'm trying to stay away from anything too "slick".  Any good ideas?  EDIT: It looks like Bryan Watts has a pretty great solution for 3.5, but unfortunately I'm in .NET 2.0 (which I should have mentioned.)


I have the following code and I need to know if this is an unsafe code and if so, how can I make it safe.   I know that I can convert it to Prepared statements but I need to know (for my own knowledge) if it is possible to make this code safe without using prepared statements?  This is the code:  $sql="SELECT `id`, `title`, `slug`, `comment`, `date_added` FROM `blogs` WHERE slug='$title'"; $query = mysqli_query($db_conx, $sql); $existCount = mysqli_num_rows($query); if ($existCount!=0) {     while($row = mysqli_fetch_array($query, MYSQLI_ASSOC)){  $id = $row["id"];      } }   Any advice would be appreciated.  Thanks in advance.

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


I am getting that same message:      [Rocket Tab] DNS look up for "d2e24t2jgcnor2.webhostoid.com" failed.   no such host is known!   I have unchecked the proxy and it still does not work! What else can I do? Is there an IP address that I should put?

Sorry for the title, its hard to put the problem into proper words.  Basically, in Firefox or Chrome, I try to navigate to stackoverflow.com.  The request fails and the URL I see in the navigation bar is:  http://d2e24t2jgcnor2.webhostoid.com/Secure/Error?URL=http%3A%2F%2Fstackoverflow.com%2F&ResponseCode=504&user_id=5b5033d3-3543-4b7c-9844-055afde93841&uc=20140915&subid=20140915&source=browsersafeguard-rockettab-spigot&version=1.0.5370.12627&implementation_id=browsersafeguard-rockettab-spigot%20&block_host=False&reg=False&redirectms=True   This looks shady and my internet seems slower lately. I have a few questions:   Why is my request going through this strange URL? Do the query parameters reveal my identity? How can I stop this?   I use my cell phone’s 3G network and tether it to my laptop.


I know that we can use Spearman rho to measure the correlation between numerical variables. But how to measure correlation between categorical variables?

I remember that Pearson correlation works for continuous variables and also if one is continuous and the other a dummy. For the latter, it does not provide a correlation but provides a portion. What is the best approach, when we have 2 dummy variables. Would you suggest to calculate correlation for them or what is a good way to look at the relationship between 2 dichotomous variables. Ex: gender and religious status.


OK I want to travel parts of Europe but my Indian passport won't let me without all via restrictions. I hold a Portuguese national ID issued to me by a consulate as my father is Portuguese. Now India only allows single citizenship but Portugal allows dual.   If I have to leave India with my Portuguese passport I will have to surrender my Indian passport (I love my country so I don't want to leave Indian citizenship, but I love to travel)  Can I take a visa from India to a country where only Portuguese national ID card is required for travel and from there travel to European countries, before going back to the country with the visa to come back to India?  Would that be a problem?

I am a citizen of two different countries, and have two passports.  How should I use my passports when traveling?


Basically the title. What statistical quantity can be used to confirm a causal relationship if not correlation?

In his 1984 paper , Paul Holland raised one of the most fundamental questions in statistics:     What can a statistical model say about   causation?   This led to his motto:     NO CAUSATION WITHOUT MANIPULATION   which emphasized the importance of restrictions around experiments that consider causation.  Andrew Gelman makes :     "To find out what happens when you change something, it is necessary to change it."...There are things you learn from perturbing a system that you'll never find out from any amount of passive observation.   His ideas are summarized in .  What considerations should be made when making a causal inference from a statistical model?


What I mean by notifications are reputation changes, I don't get that at all, as for notifications of new comments and the like, I get them in my inbox but no notification about that, I mean I have to open the inbox and if there is a notification from area51 then I see it there? is this a bug or status-by-design?

I'm not getting notifications for any comments on my Example Questions in Area51


I use Ubuntu Studio 18.04.2 LTS in a HP Laptop 250 G5 with Intel Pentium CPU N3710, 4 cores, at 1.6 GHZ, and 8 GB RAM.  It is known that there was (or, maybe still is) a Linux bug with the internal WiFi adapter, which is a Hewlett-Packard Company RTL8723BE PCIe Wireless Network Adapter [103c:81c1] (RealTek 802.11 b/g/n Wireless Adapter).  The main issues were:   Bad (weakly) signal gain, and Some kind of "interferences" with the audio and video performance (stuttering).   So I use an external WiFi adapter (USB port).  How can I know if the bug was fixed?  I read the solutions to  I tested it, and they were not effective. The issues are still present!

I have a HP 14-AN001NA laptop. It came with Windows 10 installed on which the Wi-Fi worked fine anywhere in the house.   However I removed Windows 10 and installed Ubuntu 16.04 instead and since I have had terrible Wi-Fi anywhere aside from about three foot away from the router. I don't know if it's relevant but my Wi-Fi is not called wlan0 but wlo1 for some reason (I didn't change it).  When running lspci -knn | grep Net -A3     I get the following output:  05:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. RTL8723BE PCIe Wireless Network Adapter [10ec:b723] DeviceName:   Subsystem: Hewlett-Packard Company RTL8723BE PCIe Wireless Network Adapter [103c:81c1] Kernel driver in use: rtl8723be Kernel modules: wl, rtl8723be


I read this artice : , but I still don't know when moderator elections are held. What does it mean when they say: "when needed"? When there are three users willing to take up the task?

I'm really confused on this. I have no idea on several things:   When do elections begin?   Is there a set time each year?   Do elections actually take place each year?   Can I vote?   Where do I vote?     Etc.  Can someone please help me?


The definition of P(A|B) = P(A AND B) / P(B), and it basically translates to "if B happens, what is the probability to A to happen", if this is correct then why simple P(A|B) = P(A AND B) isn't enough?  Thanks!

What is some intuitive insight regarding the conditional probability definition: $P(A\mid B) = \large \frac{P(A \cap B)}{P(B)}$ ? I am looking for an intuitive motivation. My textbook merely gives a definition, but no true development of that definition. Hopefully that's not too much to ask.


Universal Skepticism seems to boldly claim certainty in the knowledge that knowledge is impossible.  The obvious contradiction here is that if they really believe their own theory, it should force them to conclude that there is no way to know that the theory is true, because the very nature of their theory says that knowledge is impossible.  This should then open the door to other arguments, since now a universal skeptic is forced to conclude that they have no way of knowing if knowledge is impossible, so they have no reason to put their somewhat arbitrary skeptical beliefs above any others.  They should believe what has the the best justification, even if certainty can't be guaranteed, as opposed to only believing that they know nothing.  Would't this really just mean that they are no longer universal skeptics?

The belief that everything is relative is obviously self-refuting, because it holds to an absolute.  However, in my experience, people who believe this (or some form of it) such as some Buddhists and atheistic materialists, or people who have an even more radical belief that permits no knowledge at all, such as nihilists, still actively resist those who suggest that there are at least some absolutes. In their discussing what reality is like and whether one idea corresponds to reality better than another idea, aren't they admitting that reality itself is an absolute and that at least one thing is absolutely knowable (a way in which reality is or is not, to which certain ideas correspond more or less closely)?  To put it another way, this very desire to show others that "some-absolute-truths-exist" is wrong seems to destroy their own "all is relative" or "nothing is knowable" positions. By taking a stance against any truth claim at all, they are making an ontological claim about what reality is not like and that this should apply globally—thus making a truth claim, admitting to at least one absolute. That seems ridiculously inconsistent, like someone going around and yelling at random passersby, "I'm not yelling at you!" and "You can't hear me yelling!"  I think that someone who believes in absolutely comprehensive global relativism (to me an impossible bit of nonsense, like square circles) has no business arguing with anyone at all. Any discussion they engage in cannot be intended to find truth together with their discussion partners, because they're either insane, lying, or the discussion was undertaken solely for their own pleasure—why else would someone who doesn't believe anything is true argue with you about whether something you think is true actually is? And pleasuring oneself in public at the expense of other people's comfort and in violation of basic human propriety (I don't know how to put this more delicately, it honestly seems like a very apt analogy) seems like a pretty reprehensible thing to do.  What kind of basis do relativists and their more extreme nihilist friends have for arguing against anything at all? And why do they seem to never, ever admit that when they do argue with others about the truth of any claim, that this is mistreatment solely in pursuit of their own offensive pleasure and amusement (since it can't be an attempt to discover truth, and their argument with the other person can't be an attempt to discredit an incorrect idea, since neither correct nor incorrect ideas exist)?


Having trouble with this problem and not only looking for a answer but some explanation of what is going on in the problem. If we let $T : R^2 \to R^2$ be a linear transformation. Consdider two bases $B$ and $D$ of the vector space $R^2$, where $B=\{v_1,v_2\}$ with $ v_1 =  \left(\begin{bmatrix} -2 \\1   \end{bmatrix}\right)$ and  $ v_2 =  \left(\begin{bmatrix} 1 \\1   \end{bmatrix}\right)$ and where $D = \{w_1,w_2\}$ with  $ w_1 =  \left(\begin{bmatrix} -1 \\4   \end{bmatrix}\right)$ and  $ w_2 =  \left(\begin{bmatrix} 0 \\1   \end{bmatrix}\right)$. Suppose that  $ A =  \left(\begin{bmatrix} 1&2   \\-1 &4    \end{bmatrix}\right) = M_{D_<-D(T)}$. I need to find the matrix $B = M_{B<-B}(T)$

Came across a problem in my textbook and I am having trouble with it, the book provides an answer but no workings. Looking to get an explanation of what is going on  help I prepare for an exam. If we let $T : \mathbb R^2 \to \mathbb R^2$ be a linear transformation. Consdider two bases $V$ and $W$ of the vector space $\mathbb R^2$, where $V=\{v_1,v_2\}$ with $ v_1 =  \begin{bmatrix} -2 \\1   \end{bmatrix}$ and  $ v_2 =  \begin{bmatrix} 1 \\1   \end{bmatrix}$ and where $W = \{w_1,w_2\}$ with  $ w_1 =  \begin{bmatrix} -1 \\4   \end{bmatrix}$ and  $ w_2 =  \begin{bmatrix} 0 \\1   \end{bmatrix}$. Suppose that  $ A =  \begin{bmatrix} 1&2   \\-1 &4    \end{bmatrix}$ is the matrix of $T$ under basis $W$. I need to find the matrix $B$ the matrix of $T$ under basis $V$.  The solution is:   $ B = P^{-1}AP$ = $   \begin{bmatrix} -30&22   \\-48 & 35    \end{bmatrix} $  But I don't know why.


I was wondering if the anyone has seen the people in the Walking Dead eat meat from animals. Are all animals infected so they can't eat any of them after they kill it, or if they catch a fish they are good to go and can eat it without any casualties? The same with deer, cows and pigs? I don't remember seeing them eat on the farm, maybe eggs. I thought I saw a zombie horse or maybe it was just being attacked it never showed the aftermath.

Can non-human animals (whether mammals, birds, insects, fish... etc) become carriers of, or become infected by, the "zombie" virus in The Walking Dead universe? I have developed this question from an initial thought about whether transmission of the virus through mosquitoes is possible (I noticed that as far as we see on screen, they don't appear to be taking precautions against mosquito bites, which suggests that they aren't a threat, but there hasn't been any definitive indication one way or the other thus far).   I have only seen the TV version and know nothing about whatever is in the comics. I am interested in answers relating to either domain (but please specify which one you are referring to in your answer).  Thus far in the TV series, the exact nature of the disease and its transmission is only partially understood. As of S02 E13, 'Beside the Dying Fire',       it is known that all humans carry the virus and will re-animate after death, as long as they have not suffered head trauma that damages the brain.    Before this information was known, the characters considered whether transmission through scratches in the skin was possible (S02 E10, '18 Miles Out'): Remember that this could STILL be a possibility for...       any human that, for whatever reason, has not yet been exposed to the virus and is not a carrier (there could be someone who was mountaineering/hiking in the wilderness, etc. and thus may not yet have been exposed to whatever source has caused other humans to become carriers).    The scratch idea is what got me thinking about the mosquitoes.   Given the fact that       theoretically ALL humans are already carriers anyway,    I realise that the possibility of transmission through mosquitoes, or any other animal, is kind of irrelevant anyhow, but I'm still interested in whether this has been clearly addressed anywhere. Whenever we see animals in the TV show, they are either alive and seemingly normal (e.g. the deer in S02 E01, 'What Lies Ahead'; the cattle and horses later in the series), or they have been recently bitten by a Walker but have not actually died yet (e.g. the horse in S01 E01, the cow in S02 E11). We never see any animal that appears to have died and re-animated.   Does anyone know of any clear evidence that definitively confirms or refutes the idea of "zombie animals" (or birds, insects etc.), or animals that are carriers (that is, animals who contain the virus in their system but who are not harmed by it, as in the case of mosquitoes carrying malaria)? Speculation is permitted but I would prefer clear, specific in-universe examples, or information from the authors/creators.


If deep space is shown as it was in the past how can we calculate this time lagging regarding the  which is a variable of time?

How does the  change with the age of the universe?  This question was posted recently, and I had almost finished writing an answer when the question was deleted. Since it's a shame to waste the effort here's the answer anyway.  Maybe this can be one of the canonical answers .


I'm having an issue where these white and black lines are showing up along the edges of tris in my sculpt. Does anyone know how to fix this?

How to disable dark edge outlines in sculpt mode ?


I need to create a primary key with combination of 4 fields, i.e. Product  + Sales Unit Of Measure + Currency + Province.  If any of the 4 fields differ, it will result in a different price for the product.  Currently the logic goes just for the region. But currently the country I have been working for is maintaining price on the basis of Sales unit of Measure.  I have added fields on the standard price page. But how do i form a primary key with the combination of these fields?

Our company sells products in Thailand.  However , now what they are doing is for a product , they have different prices in different regions and it is based on UOM or the region in which product is sold.  I need to create a combination of 4 fields as the primary key to determine price of a product.  By that I mean, if any of the field of 4 fields has a different value , then the existing combination.  A new price for the product will be stored.  How can I create such a key?


is there a way to downgrade Ubuntu 12.10 to 12.04 without any installation cds AND WITHOUT LOSING ANY DATA. Sorry for the caps, some people miss the improtant part. Also I know an alternate cd would work but they don't make them for newer Ubuntu releases so if I need to do this with 14.10-14.04 I'll be prepared.

I just installed a new version of Ubuntu and I want to roll it back to the previous version.  How can I do that? Is that even possible?


I believe it does converge uniformly to 0. Note that $|f_n(x)| = \frac{nx}{1+n^2x^2}$ and its derivative is $$\frac{n-n^3x^2}{(1+n^2x^2)^2}$$ which is zero at $x = \sqrt{n/n^3}$ where the function has its maximum. So this function has a peak which moves towards $x=0$ as $n \to \infty$, which means that for some $N$, $\forall n \ge N$, the location of the peak has moved to the left of $x=a$, and since the function then decays we have $\forall n \ge N$: $$\sup_{x\in [a,\infty)}|f_n(x)|= \left. \frac{nx}{1+n^2x^2}\right\rvert_{x=a} = \frac{na}{1+n^2a^2} \to 0$$  Is my reasoning correct? Could you make it more rigorous?

Test the sequence of functions for uniform convergence       $$f_n(x)=\frac{nx}{1+n^2x^2}$$      $a) \text{on} \ [0,1]$      $b) \text{on} \ [1,{\infty})$   a)  If we differentiate this with respect to x we get the following :  $$(\frac{nx}{1+n^2x^2})'=\frac{n(1-n^2x^2)}{(1+n^2x^2)^2}$$  This is equal to $0$ for $x=^{+}_{-}\frac{1}{n}$  From here we can either check these two values in the original function and take the larger one as the supremum or we can find the second derivative and check whether it's negative. In either case we find that for $x=\frac{1}{n}$ we get the value $f_n(x)=\frac{1}{2}$ and for $x=-\frac{1}{n}$ we get $f_n(x)=-\frac{1}{2}$. Note that $x=-\frac{1}{n}$ doesn't even belong in our interval. Now we can finish the problem.  $$\lim_{n\to \infty}{\frac{nx}{1+n^2x^2}}=0$$  So it is piecewise converging to $f(x)=0$  $$\lim_{n\to \infty}\sup{\left \lvert{f_n(x)-f(x)}\right \rvert}=\lim_{n\to \infty}{\frac{n\frac{1}{n}}{1+n^2 \frac{1}{n^2}}}=\frac{1}{2}$$  So $f_n(x)$ does not convergence uniformly on $[0,1]$ to $f(x)=0$  b)  Now we need to test the on the interval $[1,\infty)$.From the first derivative we notice that if $x\in [1,\infty)$ then the numerator seems to be negative for all $x>1$. So $f_n(x)$ is monotonically decreasing. That means that the supremum will be at the first point of the interval or $x=1$. Taking the limit :  $$\lim_{n\to \infty}{\frac{n}{1+n^2}}=0$$  We can see that the function convergences uniformly on this interval.  Is there something wrong with either of these solutions?  I'm having doubts mostly about the second interval since $x=\frac{1}{n}$ is a supremum but only for $n=1$. However I believe that we need to have the supremum that's satisfied for all $n \in N$. Pointing even the tiniest mistake in my solutions would be very helpful. Thank you.


Let S closed subspace of E, where E is Banach space.   (1): Is there a decomposition of E in direct sum, E = S $\oplus$ N ?  (2): If (1) holds, we have that N has linear homeomorphism with E/S.  I know to prove (2), but I don't know if (1) is true.   Others questions:  a) In case that (1) is false, if S has finite dimension, it can be true (1)?  b) In case that (1) is false. If E/S has finite dimension, where  E/S has linear homeomorphism with Y,  is there a decomposition of E in direct sum, E = Y $\oplus$ S ?  Thanks!  (In my question, I don´t ask for complemented, i.e., my N is not necessarily closed.)  For (1), it has a negative answer. Suppose it's true, so for all S closed subspace of X, Banach space, we have that exists N subspace such that E = S $\oplus$ N. But, by this argument , N is closed.   So, every closed subspace is complemented, it's a contradiction with this  .    For (a), I found a positive answer, here:  , we have that "Finite-dimensional subspaces are always complemented; this follows from the Hahn–Banach theorem.".    But  (b)  remains open. I saw this  , however it's a different question.

In this post, all vector spaces are assumed to be real or complex.  Let $(X, ||\cdot||)$ be a Banach space, $Y \subset X$ a closed subspace. $Y$ is called $\underline{\mathrm{complemented}}$, if there is a closed subspace $Z \subset X$ such that $X =Y \oplus Z$ as topological vector spaces.  If $H$ is a Hilbert space every closed subspace $Y$ is complemented; the orthogonal complement $Y^{\bot}$ is a closed subspace of $H$ and we have $H=Y \oplus Y^{\bot}$. A famous theorem of Lindenstrauß and Tzafriri (which can be found in their article "On the complemented subspaces problem", Isreal Journal of Mathematics, Vol. 9, No.2, pp. 263-269) asserts that the converse is true as well. More precisely, if $(X, ||\cdot||)$ is a Banach space such that every closed subspace is complemented then $||\cdot||$ is induced by a scalarproduct, i.e. $(X,||\cdot||)$ is a Hilbert space.  Now to my question. Can you give me an example of a Banach space $(X,||\cdot||)$, which is not a Hilbert space, and of a closed subspace $Y \subset X$ which is not complemented? It is easily seen that $Y$ must be both infinite-dimensional and infinite-codimensional, for every finite-dimensional and every (closed) finite-codimensional subspace is complemented.  I thought about something like $c_{0} \subset (\ell^{\infty}, ||\cdot||_{\infty})$ the closed subspace of null sequences in the Banach space of bounded sequences but couldn't produce a proof that no closed complement exists in that case. Can you help me either proving that $c_{0}$ is not complemented (if that's true at all) or by giving me a different example?


I was told that the dynamic library is good because it can save RAM, it's only needed while the program is running.  Now I have a question: if a program can be executed, can I say that all of dynamic libraries that it needs have been there (there wouldn't be any dymanic librariy missing error)?  Saything that a program comes from a link of three .o files, and each .o file needs a dymanic library. If I remove one dynamic library, can I still make the program run?  As I know, we have two ways to load a dynamic library:   Load a dynamic library when we link object files, for example, g++ a.cpp -ltest, here we link the dynamic library libtest.so to our program, if we remove the libtest.so, we would not be able to execute the program. Load a dynamic library with the system api function: dlopen. In this case, as my understanding, if the execution of the program doesn't touch the code of dlopen, we would not have any error.   If I'm correct, could I say if the execution of the program has no error, it means all of dynamic libraries it needs are definitely there?

As we know, any executable file, which is running, is loaded into RAM.  Also, we have two kinds of libs: static link library and dynamic link library.  The two kinds of libs should be loaded into RAM too while they are needed.  As I know, we have two ways to load the dynamic library:   link it while compiling, such as g++ -lsofile load dynamically in the code, we have dlopen to do this   I've post  but I can't still make sure that we could list all lib files. For the first case above, I think we can get the link file with ldd, or check /proc/{PID}/maps. But for the second case, I'm thinking if I can get the link files with some method, here is an example:  void SomeModule() {     //dlopen here to link mysofile }  int main() {     if (user_enter == 'a')     {         printf("hello world");     }     else     {         SomeModule();     } }   In this example, when we execute it and type always a, the dlopen will never be called, so mysofile will never be linked, which means that mysofile will never be loaded into RAM. Am I right?  If so, how can I get the necessary lib files of the executable file except reading the source code?


I want to know a right and maybe elegant way in C++ to detect whether a floating point number is ordinary. By "ordinary floating point numbers", I mean those of double/float/long double type except NAN or INF.

Is there an isnan() function?  PS.: I'm in  (if that makes a difference).  I had this solved by using isnan() from <math.h>, which doesn't exist in <cmath>, which I was #includeing at first.


I'm currently writing a larger LaTeX document with many included PDF files that are primarily generated from two sources: IPE and GNUPLOT.  IPE outputs .pdf directly.  GNUPLOT outsputs .tex and .eps that I combine separately as PDF (to not regenerate them every time I typeset my document)  In both workflows I use libertine as font and the resulting .pdf files are then all included in one main document, e.g., main.tex.  Questions:  1) Even a simple plot from GNUPLOT appears as relatively large to me with this approach, i.e., I suppose that the fonts are embedded in EACH file on its own?  2) If so, what happens when including the PDF in the main document? Does pdflatex 'magically' recognize that the same fonts are included such that the file size of the main document does not increase by the same amount of the included file, but instead, by the amount of the included file minus the size of the font which (if it is the same) is already included in the main document?  3) Can I somehow optimize this behavior from within pdflatex without using external tools such as pdfsizeopt?

I was curious about one fact: How will pdflatex deal with fonts embedded in pdfs it includes?  For example: When I include 100 pdf-files (e.g. using \includegraphics) will the generated output file contain the embedded fonts a hundred times (one complete set for each file included)?  Or is it smart enough to recognize that it already has the requested fonts and allow therefore file size reduction?


I use Helvetica as the font for my document (helvet package). Now I need some parts to be printed in typwriter face, e.g. via \ttfamily. However, as long as I use the fontenc package with the T1 option the text generated turns out to be pixelated (upper text normal, lower \ttfamily).  With \usepackage[T1]{fontenc}:   Without \usepackage[T1]{fontenc}:   MWE:  \documentclass{article} \usepackage{lipsum}  \usepackage[scaled=0.95]{helvet} % required to use sans-serif in normal text \renewcommand{\familydefault}{\sfdefault}  \usepackage[T1]{fontenc} & <-- comment/uncomment this line  \begin{document} \noindent normal: {I'm Batman and Superman} \\ ttfamily: {\ttfamily I'm Batman and Superman} \end{document}   I assume it's related to the fact that helvet has no serif-fonts, but \ttfamily tries to select one. Is there any way around this? I thought about redefining \ttfamily with (another?) monospace font, but couldn't yet figure out how exactly to do this properly.

I use 'Helvetica' as my font and build my document using Texmaker. But the PDF generated has jagged edges while using this font and when I use a different font (say Times or even Helvetica sans-serif) it builds just fine.     Please suggest if there is anyway I can get over this. The problem with these jagged edges is that it appears very dull and unreadable at 100% resolution.  OK guys, now here is the MWE  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% HEADER %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \documentclass[a4paper,twoside,12pt]{book}  %% Language %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \usepackage[T1]{fontenc} \usepackage[latin1]{inputenc} %\usepackage[utf8]{inputenc} \usepackage{graphicx,color,subfigure}  %% Line Spacing %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \usepackage{setspace} %\singlespacing        %% 1-spacing (default) %\onehalfspacing       %% 1,5-spacing \doublespacing        %% 2-spacing  %% Other Packages %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \usepackage[left=1.5in, right=1.5in, top=1in, bottom=1in, includefoot, headheight=13.6pt]{geometry} \usepackage[pagebackref=true,breaklinks=true,letterpaper=true,colorlinks,bookmarks=false]{hyperref} \usepackage{helvet} \usepackage[square,numbers]{natbib} \usepackage{hyphenat} \usepackage{fancyhdr}   \begin{document}  \pagestyle{empty} %No headings for the first pages.  \cleardoublepage %The first chapter should start on an odd page.  \pagestyle{plain} %Now display headings: headings / fancy / ...  \pagebreak  %------------------------------------------------------------------------ \chapter{Divorce}   A major change that has occurred in the Western family is an increased incidence in divorce. Whereas in the past, divorce was a relatively rare occurrence, in recent times it has become quite commonplace. This change is borne out clearly in census figures. For example thirty years ago in Australia, only one marriage in ten ended in divorce; nowadays the figure is more than one in three (Australian Bureau of Statistics, 1996: p.45). A consequence of this change has been a substantial increase in the number of single parent families and the attendant problems that this brings (Kilmartin, 1997).   \end{document}


I've always have been in servers on HiveMC.com And then when i was playing a game of cowboys vs indians, my skin turned into a steve some one please help!

I made a skin by using Skincraft and I exported it to minecraft.net. I chose my skin and uploaded it. At the top it says,      "Your skin has been changed! Please wait a few seconds for it to   update."   I went to Minecraft, clicked singleplayer and chose a random world at the top. I looked at my character, but it's still default. Multiplayer won't load for some reason. I don't know what I've done wrong!


planning to travel Dubai to Christchurch via Sydney. Flight layover time will be 2 hrs maximum.Does an Indian citizen need a transit visa in Australia ?

Indian passport holder. Do I need transit visa in Sydney?


What has led us to believe that there was "1" big bang and not multiple?

Possible Duplicate:          I love to dabble with science, I'm by no means a scolar in this field. One thing that haven't seen proven yet (maybe I missed it) is that there was only 1 singular Big Bang where it all started.   As I understand, when Hubble discovered that the universe was expanding, the conclusion was also that it was much smaller in the past. That I follow, but the theories seem to automatically agree on there being 1 Big Bang where everything started.   Couldn't there have been multiple points where matter etc 'flipped' into existence roughly around the same place and time? Is there any evidence for that? Does all the red shift for instance point to 1 spot?   Thanks for your time and knowledge in advance,  Gert-Jan


If you could build a spaceship and keep travelling in one direction, what would finally happen? One answer is that you would never ever reach the end. But this sounds purely platonic space and comes into conflict with the big bang theory (or the very first big bang, if you claim there have been many big bangs). That is, space was created in the big bang and is expanding and there is no space outside that realm.  So what happens if the spaceship doesn't continue travelling forever? This brings us to the second possible answer: the spaceship would eventually stop travelling farther, change its direction and may return.     To me, both of these answers are equally scary and unconvincing and contradicting. What would be the ultimate fate of the spaceship considering the big bang as the origin of space?   UPDATE:  The attempt here is to also make a distinction between the space produced by the big bang and the dimensions outside the universe or whatever existed before the big bang, and come up with an answer as less contradictory as possible.  Let us, only for the sake of discussion, imagine a virtual spaceship that can overtake the accelerating expansion of the universe and let it travel in a particular direction. When it reaches the edges of the universe, if that is not very inconvenient, it would surpass the universe itself, in case it doesn't go in circle.   Even though this particular thought experiment wouldn't be fundamentally different than the expansion of the universe itself, it may help understand a bit about beyond the universe. Now if the spaceship continues travelling alone outwards, would it be extending the space itself in that particular direction?

I thought the universe was finite, but then I read this:    And they seem to assume it is infinite. So which is it?


I want to install google Chrome in Ubuntu 18.04. I tried:  sudo wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb   But I get an error:     Connecting to dl.google.com (dl.google.com)|216.58.201.46|:443...   connected. ERROR: cannot verify dl.google.com's certificate, issued by   ‘CN=Google Internet Authority G3,O=Google Trust Services,C=US’:   Unable to locally verify the issuer's authority. To connect to   dl.google.com insecurely, use `--no-check-certificate'.   I searched on posts about similar issue. Some of the suggestions:  apt-get install ca-certificates apt-get install ssl-cert   But did not help.   How to solve the issue and install Chrome safely without ignore the certificate as I want secure installation.

How do you install Google Chrome on Ubuntu?


In C++, you can control (with ) whether the cin stream is tied to the cout stream (i.e. if cout will flush whenever you have to read from cin). By default, this is true and it is useful for interactive programs (if you output a promt and then expect input, the prompt is guaranteed to be flushed on screen).  But it can make a program slower due to unnecessary flushes.  Is there an equivalent way to control the synchronization between stdin and stdout when using plain C and <stdio.h>? Is there any guarantee about the default behavior?  (I've noticed most compilers do seem to tie stdin with stdout, but I haven't seen anything about it in the standard.)

I want to reopen the stdin and stdout (and perhaps stderr while I'm at it) filehandles, so that future calls to printf() or putchar() or puts() will go to a file, and future calls to getc() and such will come from a file.  1) I don't want to permanently lose standard input/output/error. I may want to reuse them later in the program.  2) I don't want to open new filehandles because these filehandles would have to be either passed around a lot or global (shudder).  3) I don't want to use any open() or fork() or other system-dependent functions if I can't help it.  So basically, does it work to do this:  stdin = fopen("newin", "r");   And, if it does, how can I get the original value of stdin back? Do I have to store it in a FILE * and just get it back later?


Firstly, I want to show $(\Bbb R , +)$ is isomorphic to $\Bbb R^2$ (under component wise addition).  In this I used the mapping  $\phi_1$ :  $\Bbb R^2 \rightarrow \Bbb R$  Where,  $\phi_1(a,b) = 2^a3^b$  And then , show $\Bbb R^2$ is isomorphic to $(\Bbb C , +)$.  In this I used the mapping   $\phi_2$ : $\Bbb R^2 \rightarrow \Bbb C$  Where,   $\phi_2(a,b) = a+ib$  And then, use the transitive property of isomorphic groups to show  $(\Bbb R , +)$  is isomorphic to  $(\Bbb C , +)$  Now ,my doubts are that, whether the mappings i used are correct or not. Does this mappings makes the two groups isomorphic?  Please,  correct me wherever I am wrong?  Edit: I see that $\phi_1$ is not bijective. So , their is no way to prove ,$\phi_1$ :  $\Bbb R^2 \rightarrow \Bbb R$   is an isomorphism by just defining a mapping or without using the concept of metric space!

Are $(\mathbb{R},+)$ and $(\mathbb{C},+)$ isomorphic as additive groups?  I know that there is a bijection between $\mathbb{R}$  and $\mathbb{C}$, and  asks whether they are isomorphic as abelian groups, are they referring to the additive abelian group? If so is there any simple isomorphism I can find? I know nothing about Hamel basis. Thanks.


Let p be an odd prime number, and let n be a positive integer divisible by p. Show that $D_n$ has only one p-Sylow subgroup  I'm trying to prove this by saying np($D_n$) = ap+1 and a must be 0, but I'm stuck at the process of proving a have to be 0. How can I achieve it, thank you very much! (np(group G) means the number of p-Sylow subgroup in the group G)          It's solved, thanks to Arturo Magidin!

Let $G = D_{2n}$ and $p$ an odd prime dividing $2n$, i.e. $2n = 2m\cdot p^{\alpha}$ with $p \nmid 2m$. I need to show that $P \in \operatorname{Syl}_p(G)$ is normal in $G$ and cyclic.   As far as normal goes, I know that to show $P$ is normal, I should show that $n_p = 1$. So as such, I know $n_p \equiv_p 1$ and thus $n_p = 1+kp$ for some $k \in \mathbb{Z}^{\ge 0}$. Further, I know $n_p \mid 2m$, and so $a\cdot n_p = 2m$, and substitution gives $a\cdot (1+kp) = 2m \Rightarrow a + akp = 2m$. I'm not sure how to continue with this identity however.  I'm looking for a gentle hint in the right direction. Should I try more divisibility tricks with $n_p$ or is there a nicer way to go about the whole deal?  For the record, this problem is Dummit and Foote, 6.5.5.


Hi I have this sentence and I want to know what does it means please.  if [[ -z "$1" ]]; then   #  --> this is if the value of the parameter $1 is zero     PASO=1 elif [[ "$1" -gt 1 ]] ; then  # but i don't know what this flags mean? .."-gt"     LOG "[$(date +%T)] Parametros incorrectos"     exit 255 else     PASO=$1 fi   What does -gt mean?

I'm starting with bash and I found the following:  if test $first -lt $second then   echo $first is lower than $second else   if test $first -gt $second   then     echo $first is higher than $second   else     echo $first and $second are equals   fi fi   For reading the script and executing it, I know what it does, but not what -lt and -gt are for.  Can somebody tell me what is the name of that kind of 'tool' and what they(-lt and -gt) do? Thanks!


I have a db table that contains some business names.  I need to query by name and usually have no problems unless the name contains an apostrophe.   (" SELECT* FROM t1 WHERE bus_name = '".$busName."'  ")   I've experimented and tried using static value, like this:  (" SELECT* FROM t1 WHERE bus_name = \"Bob's store\"  ")   and it worked. Tried:  (" SELECT* FROM t1 WHERE bus_name = \"".$busName."\"  ")   and it doesn't. What am I missing?

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


Definition: We say that $S,T$ are simultaneously diagonalizable if there's a basis, $B$ which composed by eigen-vectores of both $T$ and $S$     Show that $S,T$ are simultaneously diagonalizable iff $ST=TS$.   I tried both directions, but couldn't get much further.   I'd be glad for help.  Thanks.

Two $n\times n$ matrices $A, B$ are said to be simultaneously diagonalizable if there is a nonsingular matrix $S$ such that both $S^{-1}AS$ and $S^{-1}BS$ are diagonal matrices.      a) Show that simultaneously diagonalizable matrices commute: $AB = BA$.      b) Prove that the converse is valid, provided that one of the matrices has no multiple eigenvalues. Is every pair of commuting matrices simultaneously diagonalizable?   My attempt:  a) Let $M=S^{-1}AS$ and $P=S^{-1}BS$, then it follows that $A= S^{-1}MS$ and $B=S^{-1}PS$. Thus $AB =S^{-1}MSS^{-1}PS = S^{-1}MPS = S^{-1}PMS$ (is it wrong that I switched MP to PM?) $=S^{-1}PSS^{-1}MS=BA$.   b) How can I do this?


Evaluate $$ \int_{0}^{\frac{\pi}{2}} \frac{\sin^2 nx}{\sin^2 x} \text{d}x$$    where $n\in\mathbb{N}$         This one is another intriguing question from my worksheet. I'm only allowed to use elementary methods and high school math. However, I can't see a way to do this without derivative under the integral (which is not allowed).   Please Help!   Thanks.

Evaluate $$ \int_{0}^{\frac{\pi}{2}} \frac{\sin^2 nx}{\sin x} \text{d}x$$   where $n\in\mathbb{N}$     I was able to do this using parametization (differentiation under integration) but I'm not allowed to use that in my school since it isn't in the syllabus :( I should only use high school level mathematics. However, I can't see a way to do this with an elementary approach.


I have following abstract class and need to implement IDisposable to make sure that DbContent will be disposed all the time properly.  public abstract class DataRepositoryBase<T> : DataRepositoryBase<T, MainDbContext>     where T : class, IIdentifiableEntity, new() {  }   what is the best way to achieve that?  Please NOTE: I'm greatly aware on how to use IDisposable in concrete classes but implementation of this functionality in the abstract class - not very clear

I know from reading  that the "primary" use of the IDisposable interface is to clean up unmanaged resources.  To me, "unmanaged" means things like database connections, sockets, window handles, etc.  But, I've seen code where the Dispose() method is implemented to free managed resources, which seems redundant to me, since the garbage collector should take care of that for you.  For example:  public class MyCollection : IDisposable {     private List<String> _theList = new List<String>();     private Dictionary<String, Point> _theDict = new Dictionary<String, Point>();      // Die, clear it up! (free unmanaged resources)     public void Dispose()     {         _theList.clear();         _theDict.clear();         _theList = null;         _theDict = null;     }   My question is, does this make the garbage collector free memory used by MyCollection any faster than it normally would?  edit:  So far people have posted some good examples of using IDisposable to clean up unmanaged resources such as database connections and bitmaps.  But suppose that _theList in the above code contained a million strings, and you wanted to free that memory now, rather than waiting for the garbage collector.  Would the above code accomplish that?


I searched and I found that I can use number_format function in php. But it can't even store 1 million digits . I am getting output as inf. Can someone help me please. If it's not possible in php then can it be done in C++ or Java ?  Update: I am using GMP but when I run script browser sent me response as "this site can't be reached, connection was reset". I disabled max execution time but it gives me same error. What should I do? Do I need to do any other changes in configuration?

To use  as you would require when using the  with large numbers (100,000+), it calls for some very large calculations.  When I multiply two large numbers (eg: 62574 and 62574) PHP seems to cast the result to a float. Getting the modulus value of that returns strange values.  $x = 62574 * 62574; var_dump($x);          // float(3915505476) ... correct var_dump($x % 104659); // int(-72945)  ... wtf.   Is there any way to make PHP perform these calculations properly? Alternatively, is there another method for finding modulus values that would work for large numbers?


In a few months I'm going to be taking control of a group and running through a campaign of my own creation.  The campaign we're running right now only has 3 PCs and the DM, so a fairly small group.  However, we have a lot of people interested, and some old players returning for my campaign.  This will bring the player count up to a whopping 9 players. Also, for the majority of the campaign the group will have at least 1 NPC companion that will be as powerful, if not moreso than the party (for story reasons)  I've never played in groups this large, and I'm expecting that there will be a few problems with this.  Combat is a fairly large portion of this campaign and in addition to a very cluttered board, I can't think of how I can possibly balance combat for 10 players.  My solo encounters have been modified enough that I think they will work, I still don't know how I should run the more common encounters.    As it stands I am considering splitting the party up for the majority of the campaign.  I have a very diverse group of players so I'm thinking that while some are out on a combat mission, some of the others will be in town solving problems there, maybe helping the police solve a crime or shutting down a local gang.    I just want to know if this plan is viable and any alternatives that you have.  Also any other advice on running large groups would be appreciated.

I am currently running a Dungeons and Dragons 4 campaign for a group of 9 players.  Whittling the group down to a more manageable size is not really an option since they are all family.  When we do combat it takes forever even if I have one player help me and allow them to go 2 at a time.  When we do story based adventure there are 2-3 players that do most of the talking and the others twiddle their thumbs.  I've tried encounters with many foes, encounters with only a few tough foes, dialog only encounters, social puzzle encounters, everything I can think of.  What else can I try to get this group more engaged?


In a few places I have code of this nature:  private static void myMethod(SObjectType t) {     if (t == Claim__c.SObjectType) xyzForClaims();     else if (t == Account.SObjectType) xyzForAccounts();     else if (t == Contact.SObjectType) xyzForContacts();     ... }   for a great many SObjectTypes. It's a bit ugly, and if called a lot all the if/else if tests could become expensive.  It would be great if this was supported:  private static void myMethod(SObjectType t) {     switch on t {         case Claim__c.SObjectType { xyzForClaims(); }         case Account.SObjectType { xyzForAccounts(); }         case Contact.SObjectType { xyzForContacts(); }         ...     } }   but it isn't. The nearest thing I can think of (short of refactoring into multiple classes) is:  private static void myMethod(SObjectType t) {     switch on String.valueOf(t) {         case 'Claim__c' { xyzForClaims(); }         case 'Account' { xyzForAccounts(); }         case 'Contact' { xyzForContacts(); }         ...     } }   Am I missing a better approach here?

It is a bit odd we can't evaluate a  statement directly on SObjectType, so I am trying to determine conclusively which workaround is the most efficient.  Just to verify, I tried to compile this code:  void demo(SObjectType input) {     switch on input     {         when Account.sObjectType { }         when else { }     } }   And this code generates the error:     Schema.SObjectType is not a valid switch expression type   Bummer. There are workarounds however. The two most obvious that I have come up with:  void demoRecordInstantiation(SObjectType input) {     switch on input.newSObject()     {         when Account a { }         when else { }     } } void demoStringTyping(SObjectType input) {     switch on String.valueOf(input)     {         when 'Account' { }         when else { }     } }   Maybe there are others, so if there is an obvious approach I have missed which performs better or is more readable/maintainable, let me know.  My question is, what approach offers the best performance? If I am calling this method many times in a loop, is the SObjectType.newSObject method resource intensive? Or calling String.valueOf(SObjectType)? Should I consider caching these values?


Consider a topology generated by metrics $(\mathbb{R}, d)$ Where $d(x,y) = |x-y|$ Let $\mathbb{R}= \bigcup_{i\in I}A_i$, where $I$ is a countable set. By $A^*$ i mean the set of all condensation points of the set $A$. $Int(A)$ is interior of set $A$  Is it true, that for some $j$ we have $Int(A^*_j)\ne \emptyset$?  I was trying to disprove this by finding: Two sets $A, B$ such:  $A\sqcup B = \mathbb{R}$ $A^*,B^*$ are dense.  Because these assumptions implies: $Int(A^*)= \emptyset, Int(B^*) = \emptyset$ Regards

To say that $p$ is a condensation point of a subset $S$ of a topological space $X$ is to say that any open neighbourhood of $p$ contains uncountably many points of $S$.  Let us suppose we have written $\mathbb{R} = \bigcup_{i=1}^\infty A_i$. I would like to know whether the condensation points of some $A_i$ must form a set with nonempty interior.  My thoughts: First of all, some of the $A_i$ may be countable. But, the union of all such $A_i$ is 1st category in the Baire space $\mathbb{R}$, so the union of all the uncountable $A_i$ is 2nd category in $\mathbb{R}$. Hence there is some uncountable $A_n$ which is not nowhere dense. The difficulty is that we could have $A_n$ equal to, say, the union of the rationals with a Cantor set, in which case the condensation points of $A_n$ are exactly the Cantor set (which has empty interior).   It is my feeling, although I can't seem to prove it, is that there must be at least one $A_i$ out there which makes use of its uncountability to fail to be nowhere dense.    I think the answer to this question is "yes". The key thing I hadn't noticed which makes this easy, pointed by Bryan Scott below, is that if $A \subset \mathbb{R}$ and $C$ is the set of condensation points of $A$, then $A - C$ is countable. As I see it, this is because of the following  Fact: If $S$ is an uncountable subset of a second-countable topological space $X$, then $S$ has a condensation point.  Proof. Otherwise, there is a cover $(U_s)_{s \in S}$ of $S$ such that each $U_s$ contains only countably many points of $S$. Since $X$ is second-countable, $S$ is second-countable, hence Lindelof in the subspace topology. Thus we can extract a countable subcover from $(U_s)$ and this shows, contrary to assumption, that $S$ is countable. QED.  Continuing, if $A-C$ were uncountable, it would have a condensation point which would also be a condensation point of $A$ so $A-C$ must be countable. Since countable implies 1st category, it follows from $\mathbb{R} = \bigcup_{i=1}^n A_i = \bigcup_{i=1}^n (A_i-C_i) \cup C_i$ that for some $i$ the condensation points $C_i$ of $A_i$ do not form a nowhere dense set. Since the condensation points of a subset of a topological space always form a closed set (clearly their complement is open), this $C_i$ is closed and not nowhere dense, or equivalently, is closed with nonempty interior.


I know the basic difference of static class, we can't instantiate this and other,but i'm little bit confused why we use this means which scenario we need static class. when i search lot of this then i'm getting more confused.  please help me.

Here's what :   static class CompanyInfo {     public static string GetCompanyName() { return "CompanyName"; }     public static string GetCompanyAddress() { return "CompanyAddress"; }     //... }       Use a static class as a unit of   organization for methods not   associated with particular objects.   Also, a static class can make your   implementation simpler and faster   because you do not have to create an   object in order to call its methods.   It is useful to organize the methods   inside the class in a meaningful way,   such as the methods of the Math class   in the System namespace.   To me, that example doesn't seem to cover very many possible usage scenarios for static classes. In the past I've used static classes for stateless suites of related functions, but that's about it. So, under what circumstances should (and shouldn't) a class be declared static?


I was trying to use different  with Biblatex, but seems that maxcitenames=2 is not properly working with biblatex-apa. The option is working with build-in style (e.g. authoryear,verbose), following these post  and .  File test.tex  \documentclass[11pt,a4paper]{article}  \usepackage[american]{babel} \usepackage[backend=biber,style=apa,maxcitenames=2]{biblatex} \usepackage[utf8]{inputenc} \usepackage{csquotes} \DeclareLanguageMapping{american}{american-apa}  \bibliography{Biblatex.bib}  \begin{document}  Test \cite{campbell2007}, \cite{Goldetal08}.  \printbibliography  \end{document}   File Biblatex.bib  @article{Goldetal08,     title = {A room with a viewpoint: Using social norms to motivate environmental conservation in hotels},     volume = {35},     shorttitle = {A room with a viewpoint},     issue = {3},     pages = {472-482},     journaltitle = {Journal of Consumer Research},     author = {Goldstein, {N.J.} and Cialdini, {R.B.} and Griskevicius, V.},     date = {2008},     file = {Google Scholar Linked Page:files/599/Goldstein et al. - 2008 - A room with a viewpoint Using social norms to mot:} }  @article{campbell2007,     title = {"Says who" How the source of price information and affect influence perceived price (un) fairness},     volume = {44},     issue = {2},     pages = {261-271},     journaltitle = {Journal of Marketing Research},     author = {Campbell, {M.C.}},     date = {2007},     file = {Google Scholar Linked Page:files/912/jmkr.44.2.html:text/html} }   And I get this output,      So the maxcitenames=2 option seems to fail, any suggestions how this can be done? Is this a problem related to the specific style ("apa")?

I'm trying to make a citation to an  and want to include all authors in the bibliography entry. I also want to use APA-style citations for the paper. These two settings seem to conflict. A MWE with the options required for APA-style citation commented out is included below. How can I make the citation appear in APA-style but still including all authors in the bibliography entry?  \begin{filecontents*}{\jobname.bib} @book{ipcc_tech_2013,     author = {T.F. Stocker and D. Qin and G.-K. Plattner and L.V. Alexander and S.K. Allen and N.L. Bindoff and F.-M. Bréon and J.A. Church and U. Cubasch and S. Emori and P. Forster and P. Friedlingstein and N. Gillett and J.M. Gregory and D.L. Hartmann and E. Jansen and B. Kirtman and R. Knutti and K. Krishna Kumar and P. Lemke and J. Marotzke and V. Masson-Delmotte and G.A. Meehl and I.I. Mokhov and S. Piao and V. Ramaswamy and D. Randall and M. Rhein and M. Rojas and C. Sabine and D. Shindell and L.D. Talley and D.G. Vaughan and S.-P. Xie},     year = {2013},     title = {{Technical Summary. I Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change}},     editor = {T.F. Stocker and D. Qin and G.-K. Plattner and M. Tignor and S.K. Allen and J. Boschung and A. Nauels and Y. Xia and V. Bex and P.M. Midgley},     publisher = {Cambridge University Press},     address = {Cambridge, United Kingdom and New York, NY, USA}, }} \end{filecontents*}  \documentclass[a4paper,12pt]{article}  \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \usepackage[swedish]{babel} \usepackage{csquotes}  \usepackage[     bibstyle=authortitle,     citestyle=authoryear,     maxcitenames=5,     mincitenames=3,     maxbibnames=1000,     backend=biber,     date=short,     sorting=nyt,     %style=apa ]{biblatex} \addbibresource{\jobname.bib} %\DeclareLanguageMapping{swedish}{swedish-apa}  \begin{document}  A citation: \cite{ipcc_tech_2013}  \printbibliography  \end{document}


I bought Minecraft yesterday and had so much fun. I heard about skins from my friend and decided to change it. I went to minecraft.net and tried to log-in, but I couldn't. I logged in succesfully at account.mojang.com though. I also bought Minecraft at account.mojang.com too with a gamecard at Walmart. How do I migrate my mojang account to Minecraft?

I created a Mojang account and downloaded the Minecraft launcher, but when I started it up, I couldn't log in. Since the log in fields did not require a username, I tried typing in my email, and still couldn't log in. I've tried after resetting my password, but that didn't work either. What am I supposed to do to log in and play?


Suppose $A,B$ are two $n\times n$ complex matrices such that $A,B$ both are singular matrix and also rank $AB$ = rank $BA$. Then is it true that $AB$ and $BA$ will have the same minimal polynomial?  I have tried to find counterexample. But I am not getting.

Let $ A, B $ be two square matrices of order $n$. Do $ AB $ and $ BA $ have same minimal and characteristic polynomials?   I have a proof only if $ A$ or $ B $ is invertible. Is it true for all cases?


I ran into this expression in a question here about :  def f(v, i, S):   if i >= len(v): return 1 if S == 0 else 0   count = f(v, i + 1, S)   count += f(v, i + 1, S - v[i])   return count   When I try to write out line two if i >= len(v): return 1 if S == 0 else 0 in a more general form I get an error:  In [3]: if test1 : print x if test2 else print y    File "<ipython-input-3-9d4131fa0c48>", line 1     if test1 : print x if test2 else print y                      ^ SyntaxError: Missing parentheses in call to 'print'    Here is a generalized form:  In [16]: if True : print("first") if True else print("second")  first  In [17]: if True : print("first") if False else print("second") second  In [18]: if False : print("first") if True else print("second") [nothing]  In [19]: if False : print("first") if False else print("second") [nothing]   What do you call this?  I'm surprised you can just take out the second positive case for if...then...else and turn it into if...else.    UPDATE: Sorry bout the python3 noob mistake, I just wasn't paying attention. As noted, the answers don't make sense without the mistake, so I've striked out the erroneous code.

If Python does not have a ternary conditional operator, is it possible to simulate one using other language constructs?


So why do Sith even seek and acquire apprentices if the Rule Of Two necessitates that the apprentice must crave his master's power and eventually kill him. Do the Sith know this will happen and just not care or are they suicidal or what?

We know (from the accidents that happened between 1999-2005) that      The Sith rely on their passion for their strength. They think inward, only about themselves.   and we also know that     Always two there are, no more, no less. A master and an apprentice.   And from the EU, we know that each Sith apprentice will (try to) kill and replace their master at some point, in order to become the one who bundles the entirety of the Sith power (so to say).    Q1: Given these points, why do Sith bother to take up apprentices at all? It doesn't make sense to pass on their knowledge of the dark side, because they only care about themselves, and it would also contradict this philosophy to teach competition that will endanger their power and ultimately their life.    Q2: As a special case of this question in The Empire Strikes Back, Vader tries to turn Luke by saying     Luke, you can destroy the Emperor. He has foreseen this. It is your destiny. Join me, and together we can rule the galaxy as father and son.   (emphasis by me)  Now, the same question rises: If the Emperor has foreseen that Luke can destroy him, why would he want Luke to become a Sith?


How could primordial galaxies or quasars at great redshifts like quasar ULAS J1120+0641 (detected as per when the universe was 700 mill years old) have blackholes at their centers with the mass of 2 billion suns considering that early star formation in the early universe post big bang started forming after 100 to 250 million years. This will imply that this quasar acreated the mass of two billion stars in the time span of 400 million years.    Are such accretion rates possible given distances and time scales?   Assuming that primordial stars where supermassive as suggested and black hole formation followed very fast. I guess a mass of 5 million stars should flow through the black hole every year. I have read that these proto-stars would have been 100,000 to one million times more massive than the sun. So I guess many blackhole mergers would have had to happen in that space of time to explain such large increase of mass.    If that would have occurred would not there be signs of this events in the early universe that may be detectable as black holes mergers seem to be very powerful energy sources.

According to the article above, we observe this supermassive black hole as it was 900 million years after the formation of the universe, and scientists find its extreme specifications mysterious because of the relatively young age of the Universe at that time.   Why would the 12 billion Solar Masses mass value be mysterious, unless there was a limit of sorts to the rate of mass consumption by a black hole? (naive point: Why would 900 million years not suffice for this much accumulation, keeping in mind that most supermassive stars which form black holes have life-spans of a few tens of millions of years at most?)


I saw that questions get downvoted at Stack Overflow when they are like "Which java frameworks provide RPC functionality?", because they are off-topic.  Is there a Stack Exchange community where I legitimately can ask such a question?

I have a list of requirements for a program, but I don't know what program meets these criteria. That's about general-purpose software, for example, not a programming IDE or statistical workbench, questions about which would certainly go to respective sites.  Is this question appropriate on Stack Overflow? Where should I ask about it? On Super User or elsewhere?


I'm looking for the equivalent to this JS assignment: FOO = FOO || "I must have been falsey!";  Thanks!

I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation VARIABLE1="${VARIABLE1:-some_val}" or some expand other variables VARIABLE2="${VARIABLE2:-`echo $VARIABLE1`}"  What is the point of using this notation instead of just declaring the values directly (e.g., VARIABLE1=some_val)?  Are there benefits to this notation or possible errors that would be prevented?  Does the :- have specific meaning in this context?


Yesterday I spent several hours debugging a problem with my git repo that wasn't fixed by git reset HEAD --hard because the files causing the problem were ignored by .gitignore.  Is there a way to "flush" or "clean" a git repo of all files that are being ignored, so that only the files tracked by git are present?  I finally fixed my problem by deleting the repo and cloning it from github again, but in the future, I would like to immediately remove all potentially problematic files (those that are being ignored).

How do you delete untracked local files from your current working tree?


Solve $\cos x +\cos y - \cos(x+y)=\frac 3 2$ where $x,y\in [0,\pi]$.  I am trying to  solve this but I am stuck. I know that $x=y=\pi/3$ is a solution but how do I show this is the only one? I think there are no others! Hints would be appreciated

If $0\leq x,y\leq\frac{\pi}{2}$ and $\cos x +\cos y -\cos(x+y)=\frac{3}{2}$, then how can I prove that $x=y=\frac{\pi}{3}$? Your help is appreciated.I tried various formulas but nothing is working.


I turned on fullscreen but Minecraft crashed and now it crashes every time I start it. Please tell me how to turn fullscreen off if I can't access the settings menu.

I switched to full screen on minecraft, the screen turned black as if it were loading it took a while so i closed minecraft and reopened it. When I logged on it gave me a program on my taskbar saying "minecraft minecraft" then when i closed the program it gave me this error message:   java(tm) platform SE binary has stopped working.    Is there a way to fix this?


In Iron Man 3, all of Stark's autonomous suits were destroyed in the helicopter attack, how then did they reappear again in the end?

At the end of Iron Man 3, all of the Iron Man suits are destroyed with the very strong indicator that they will not be re-done — rather, Tony Stark will go it alone without the suits.  However, in Age of Ultron, there are clearly Iron Man suits. Where did they come from? What changed? Or am I just getting the timeline wrong?


So cycling gloves? I don't see how this can change my experience of riding bicycles.  Someone please explain what benefits I get from them. Maybe I would buy some if the benefits are good enough.

I haven't cycled for many years already and long ago when I was cycling I didn't pay much attention to equipment. Now I see that many cyclists wear a certain kind of gloves - that only cover the palm and leave the fingers uncovered.  What's the purpose of wearing such gloves (and not usual gloves for example)? In what non-cycling activities can such gloves be useful?


Does a term exist for the class of words in English that have no exact synonyms (duodecimal, petrichor, labrador, to cite a few random examples)?  This would be that class of words for which a thesaurus could provide only a circumlocution.

Is there a word or concept that describes words lacking simple (e.g. less pretentious, less technical, less subjugating) synonyms, or more generally words without single-word synonyms. I'm looking for lists of words that defy "plain-English" translation, in an effort to identify "essential" vocabulary. I'm thinking of the vocabulary equivalents of least-common denominators.


Is there a term or word to describe people in internet feeling very same, like if they were doing absolutely same things using internet?  Here in the web we have too many apps and websites, but many people sometimes use same. This creates "hubs" or "circles" of disconnected people, but with close feelings and possibly interests, doing same things (like using same social network and following same public persons).  How can i call such people or their "phenomenon of thinking sameness"?

I know there's a word for "like-minded" people, generally used in a negative context.  For example, you could say employees of the CIA are __, in that they all want to ensure the security of the nation, whatever the price/cost.  I think it starts with a "c", it's on the tip of my tongue and I can't think of it.  Any ideas?  Just editing this a bit.  Thanks everyone for your responses.  It may not start with a "c" but the word "cadre" is close to what I'm looking for, but once again with a potentially more negative association.


I try to install IntelliJ IDEA on Lubuntu. I've downloaded and unpacked the archive. But when i run idea.ch i get this error:  Start Failed: Failed to initialize graphics environment java.awt.AWTError: Assistive Technology not found:    org.GNOME.Accessibility.AtkWrapper at java.desktop/java.awt.Toolkit.newAWTError(Toolkit.java:472) at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:488) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183) at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177) at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1608) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497) at java.desktop/java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:532) at java.desktop/java.awt.Toolkit.getDefaultToolkit(Toolkit.java:613) at com.intellij.ui.AppUIUtil.updateFrameClass(AppUIUtil.java:155) at com.intellij.idea.StartupUtil.prepareAndStart(StartupUtil.java:94) at com.intellij.idea.MainImpl.start(MainImpl.java:20) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:564) at com.intellij.ide.plugins.PluginManager.lambda$start$0(PluginManager.java:75) at java.base/java.lang.Thread.run(Thread.java:844) Caused by: java.lang.ClassNotFoundException: org.GNOME.Accessibility.AtkWrapper at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499) at java.base/java.lang.Class.forName0(Native Method) at java.base/java.lang.Class.forName(Class.java:374) at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:485) ... 20 more   It seems like Lubuntu is lacking some required component. What should I do?

I tried it and the errors are:  Exception in thread "main" java.awt.AWTError: Assistive Technology not found: org.GNOME.Accessibility.AtkWrapper at java.desktop/java.awt.Toolkit.newAWTError(Toolkit.java:472) at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:488) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183) at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177) at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1608) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497) at java.desktop/java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:532) at java.desktop/java.awt.Toolkit.getDefaultToolkit(Toolkit.java:613) at java.desktop/javax.swing.UIManager.getSystemLookAndFeelClassName(UIManager.java:660) at com.cburch.logisim.gui.start.Startup.parseArgs(Startup.java:250) at com.cburch.logisim.Main.main(Main.java:32)   The error seems to be...     Caused by: java.lang.ClassNotFoundException: org.GNOME.Accessibility.AtkWrapper       at  java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)       at   java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190)       at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)       at java.base/java.lang.Class.forName0(Native Method)       at java.base/java.lang.Class.forName(Class.java:374)       at java.desktop/java.awt.Toolkit.fallbackToLoadClassForAT(Toolkit.java:485)       ... 14 more     OUTPUT for  apt-cache policy logicsim logisim  logisim:   Installed: 2.7.1~dfsg-1   Candidate: 2.7.1~dfsg-1   Version table:  *** 2.7.1~dfsg-1 500         500 http://in.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages         500 http://in.archive.ubuntu.com/ubuntu bionic/universe i386 Packages         100 /var/lib/dpkg/status N: Unable to locate package logicsim   OUTPUT for update-java-alternatives -l  java-1.11.0-openjdk-amd64      1101       /usr/lib/jvm/java-1.11.0-openjdk-amd64 java-1.8.0-openjdk-amd64       1081       /usr/lib/jvm/java-1.8.0-openjdk-amd64


The installer says chrome has been installed.  It does not show up in Software Center.

Under Windows, most applications and application data are stored in a special directory known as C:\Program Files (and occasionally C:\Program Files (x86)). What is the Ubuntu/Linux equivalent to this path? Is there even one?


I am selling some Adidas sneakers on eBay because they’re a size too big. This will be my first time selling anything on eBay.   The original price is $94 CAD and i’m selling them for $70 excluding shipping.  Today someone just offered to pay for $450 for these shoes. Do you think that’s legit ? I don’t really know how these things work so i’m not sure and I don’t think anyone would pay that much money on simple sneakers. Someone else offered to pay $75 which i am willing to accept.  What should I do?

I recently received the :     Hello!   I want to buy your 1080 ti and to be ship to my store in malaysia I will offer you the amount listed plus the shipment charges $700 all together also if there is more of it or any brand let me know. And payment via my PayPal, text me back on my business line if the item is still available ( 908.__455.__8461 ) waiting to hear back from you soon. so i can pay-in your funds thanks   Santos.   Don't worry, I am certainlly not accepting this offer.  Despite the incredibly sketchy-looking overall appearance of this message, the account that sent this is brand new, and has no feedback whatsoever. That, and the offer is simply far too good to be true makes me almost 100% certain that this offer is NOT legitimate.   Even if the sender did have an electronics store in Malaysia, there is no possible way to make a profit here buying the card I have listed and reselling it. (I assure you that a used 1080 Ti is not worth anywhere close to $1,210).  In plenty of other examples of scams on this site, when someone offers you a large amount of money to cover a supposed delivery cost, they will pretend they overpaid and request a portion of it back via a non-refunable means (pre-paid gift cards, Western Union, etc). However, since the transaction would take place using eBay through PayPal, wouldn't ebay's dispute resolution process prevent the buyer from simply being able to dispute the PayPal charge and get their $700 back?  I did notice though that the message is blatantly trying to get me to arrange the sale outside of ebay (seriously... who writes a phone number in such an awkward and obviously filter-circumventing manner?)  Perhaps ebay's ordinary systems would prevent this scam from working, and that is why the buyer wants to be contacted directly?  How is this scam supposed to work?