<p dir="auto">I've recently updated scipy in Fedora to newest 0.13.0 release and I can see one test failure on every architecture, both in python 2 and 3:</p>
<h5 dir="auto">Python 3.3.2</h5>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="ERROR: test_fitpack.TestSplder.test_kink
----------------------------------------------------------------------
Traceback (most recent call last):
  File &quot;/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/fitpack.py&quot;, line 1178, in splder
    c = (c[1:-1-k] - c[:-2-k]) * k / dt
FloatingPointError: invalid value encountered in true_divide
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File &quot;/usr/lib/python3.3/site-packages/nose/case.py&quot;, line 198, in runTest
    self.test(*self.arg)
  File &quot;/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/tests/test_fitpack.py&quot;, line 329, in test_kink
    splder(spl2, 2)  # Should work
  File &quot;/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/fitpack.py&quot;, line 1186, in splder
    &quot;and is not differentiable %d times&quot;) % n)
ValueError: The spline has internal repeated knots and is not differentiable 2 times"><pre class="notranslate"><code class="notranslate">ERROR: test_fitpack.TestSplder.test_kink
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/fitpack.py", line 1178, in splder
    c = (c[1:-1-k] - c[:-2-k]) * k / dt
FloatingPointError: invalid value encountered in true_divide
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/lib/python3.3/site-packages/nose/case.py", line 198, in runTest
    self.test(*self.arg)
  File "/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/tests/test_fitpack.py", line 329, in test_kink
    splder(spl2, 2)  # Should work
  File "/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python3.3/site-packages/scipy/interpolate/fitpack.py", line 1186, in splder
    "and is not differentiable %d times") % n)
ValueError: The spline has internal repeated knots and is not differentiable 2 times
</code></pre></div>
<h5 dir="auto">Python 2.7.5</h5>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="ERROR: test_fitpack.TestSplder.test_kink
----------------------------------------------------------------------
Traceback (most recent call last):
  File &quot;/usr/lib/python2.7/site-packages/nose/case.py&quot;, line 197, in runTest
    self.test(*self.arg)
  File &quot;/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python2.7/site-packages/scipy/interpolate/tests/test_fitpack.py&quot;, line 329, in test_kink
    splder(spl2, 2)  # Should work
  File &quot;/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python2.7/site-packages/scipy/interpolate/fitpack.py&quot;, line 1186, in splder
    &quot;and is not differentiable %d times&quot;) % n)
ValueError: The spline has internal repeated knots and is not differentiable 2 times"><pre class="notranslate"><code class="notranslate">ERROR: test_fitpack.TestSplder.test_kink
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python2.7/site-packages/scipy/interpolate/tests/test_fitpack.py", line 329, in test_kink
    splder(spl2, 2)  # Should work
  File "/builddir/build/BUILDROOT/scipy-0.13.0-1.fc21.arm/usr/lib/python2.7/site-packages/scipy/interpolate/fitpack.py", line 1186, in splder
    "and is not differentiable %d times") % n)
ValueError: The spline has internal repeated knots and is not differentiable 2 times
</code></pre></div>
<h4 dir="auto">Setup</h4>
<p dir="auto">numpy 1.8.0<br>
atlas 3.10.1<br>
blas 3.4.2<br>
lapack 3.4.2</p>
<h4 dir="auto">Build logs:</h4>
<p dir="auto"><a href="http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/armv7hl/build.log" rel="nofollow">http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/armv7hl/build.log</a><br>
<a href="http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/i686/build.log" rel="nofollow">http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/i686/build.log</a><br>
<a href="http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/x86_64/build.log" rel="nofollow">http://kojipkgs.fedoraproject.org/packages/scipy/0.13.0/1.fc21/data/logs/x86_64/build.log</a></p>
<p dir="auto"><code class="notranslate">eigs</code>, <code class="notranslate">eigsh</code>, <code class="notranslate">svds</code> all default to using <code class="notranslate">2 * k + 1</code> for the number of lanczos vectors <code class="notranslate">ncv</code>. This is fine for <code class="notranslate">k &gt; ~5</code> or so but drastically slows the algorithm down for small <code class="notranslate">k</code> (e.g. k=2 or 1 slower than k=6!) and often means the convergence fails. The problem is worse for dense matrices (these sparse methods are actually very useful for dense matrices as well).</p>
<p dir="auto">The optimum value depends on <code class="notranslate">n, k,</code>, the sparsity and other factors, but should generally should be <code class="notranslate">&gt;= 10</code>. Matlab apparently uses 20 as its minimum for equivalent functions but this might be a bit high for small sparse matrices.</p>
<p dir="auto">There might be a method of choosing <code class="notranslate">ncv</code> intelligently? But setting it to at minimum <code class="notranslate">10</code> would be a quick fix.</p>