<p dir="auto">Hello,<br>
My issue is about lowpass generated in sos form</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="&gt;&gt;&gt; print(signal.butter(2, 1, 'low', analog=True, output = &quot;sos&quot;))
&gt;&gt;&gt; print(signal.butter(2, 1, 'high', analog=True, output = &quot;sos&quot;))
[[1.         0.         0.         1.         1.41421356 1.        ]]
[[1.         0.         0.         1.         1.41421356 1.        ]]"><pre class="notranslate"><code class="notranslate">&gt;&gt;&gt; print(signal.butter(2, 1, 'low', analog=True, output = "sos"))
&gt;&gt;&gt; print(signal.butter(2, 1, 'high', analog=True, output = "sos"))
[[1.         0.         0.         1.         1.41421356 1.        ]]
[[1.         0.         0.         1.         1.41421356 1.        ]]
</code></pre></div>
<p dir="auto">As you can see generating a lowpass and a highpass gives the same coefficients.<br>
Same issue with the cheby1 filter type.<br>
Like the sos configuration doesn't like to see b2 = 0<br>
Cheers,</p>
<p dir="auto">Hello,<br>
I have realized about an issue with sparse matrixes and loadmat function.<br>
I have a set of sparse matrixes for storing very sparse values. Sometimes they are so sparse that some of the matrixes are never used, so they keep on zeros.</p>
<p dir="auto">When I try to save them in a matlab file and load them again  I always find the same problem, invalid shape. I know that the sparse matrixes should have at leas 1 element, and 2 dimensions, but the content of the matrixes is data-driven.</p>
<p dir="auto">My point is that is not real the sparse has no shape, it is just there is no active elements in that moment. Is this a known feature? it is a new bug?</p>
<p dir="auto">Thabks for your help and sorry if it is duplicated, but I didn't find any other issue with a similar description.</p>