# [SciPy-user] spline interpolation

Christian Kristukat ckkart at hoc.net
Fri Nov 10 06:07:32 CST 2006

```Nils Wagner wrote:
> Christian Kristukat wrote:
>> Robert Kern wrote:
>>
>>> Jordan Dawe wrote:
>>>
>>>> I've been looking at scipy's interpolation routines and I can't make
>>>> heads or tails of them.  I just want to do a spline interp1d like matlab
>>>> does.  Is there any way to do this?
>>>>
>>> I don't know exactly what features you want from Matlab's interp1d, but you
>>> probably want scipy.interpolate.UnivariateSpline.
>>>
>> I just noticed that UnivariateSpline.derivatives() seems to be broken:
>>
>> import numpy as N
>> from scipy.interpolate import UnivariateSpline as spline
>> x=N.arange(10,dtype=float)
>> y=x**2
>> a=N.linspace(2,5,100)
>> sp=spline(x,y)
>> b=sp(a)
>> der=sp.derivatives(a)
>>
>> fails with:
>>
>> 0-th dimension must be fixed to 8 but got 4
>> ---------------------------------------------------------------------------
>> dfitpack.error                                     Traceback (most recent call last)
>>
>> /mnt/home/ck/<console>
>>
>> /usr/local/lib/python2.4/site-packages/scipy/interpolate/fitpack2.py in
>> derivatives(self, x)
>>     179     def derivatives(self, x):
>>     180         """ Return all derivatives of the spline at the point x."""
>> --> 181         d,ier = dfitpack.spalde(*(self._eval_args+(x,)))
>>     182         assert ier==0,`ier`
>>     183         return d
>>
>> error: failed in converting 2nd argument `c' of dfitpack.spalde to C/Fortran array
>>
>> with numpy 1.0rc2, scipy 0.5.1 on linux
>>
>> Christian
>>
>>
>> _______________________________________________
>> SciPy-user mailing list
>> SciPy-user at scipy.org
>> http://projects.scipy.org/mailman/listinfo/scipy-user
>>
> Works fine for me.
>
>>>> der
> array([  4.00000000e+00,   4.00000000e+00,   2.00000000e+00,
>         -1.92438658e-15])
>>>> N.__version__
> '1.0.1.dev3432'
>>>> scipy.__version__
> '0.5.2.dev2314'

Thanks for trying. But I don't understand the result. Why does it have 4
elements, when b had 100? What is meant by 'return all derivatives'? Is that
'all derivatives until the derivative is zero'?

Christian
```