<p dir="auto">scipy.interpolate.insert allows for inserting a knot (with an arbitrary multiplicity) in a B-spline between two knots (say u_i and u_{i+1}) without modifying the others knots, as described in "Inserting new knots into B-spline", W. Boehm, Comp.-Aided Design 12(4), pp.199-201, 1980.<br>
I have code that relies on that property and worked well for the past few years (since 2010).</p>
<p dir="auto">Some change may have been committed that did not respect this non-modification of knots, see attached minimal example where for a simple knot sequence (obtained with splprep) some knot is deleted (6), another one is inserted (5 with multiplicity going from 1 to 2).</p>
<p dir="auto">Has anybody experienced that already ? A clue on the commit that introduced that ?</p>
<p dir="auto">From <a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/opoplawski/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/opoplawski">@opoplawski</a>: With Fedora Rawhide (but not Fedora 19) I'm seeing:</p>
<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-0.13.0-0.1.b1.fc21.x86_64/usr/lib64/python2.7/site-packages/scipy/interpolate/tests/test_fitpack.py&quot;,
line 326, in test_kink
     splder(spl2, 2)  # Should work
   File
&quot;/builddir/build/BUILDROOT/scipy-0.13.0-0.1.b1.fc21.x86_64/usr/lib64/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-0.13.0-0.1.b1.fc21.x86_64/usr/lib64/python2.7/site-packages/scipy/interpolate/tests/test_fitpack.py",
line 326, in test_kink
     splder(spl2, 2)  # Should work
   File
"/builddir/build/BUILDROOT/scipy-0.13.0-0.1.b1.fc21.x86_64/usr/lib64/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>
<p dir="auto">and the same with python3.</p>