[SciPy-user] problems with splrep,splev

Christian K. ckkart@hoc....
Sat Apr 18 08:31:23 CDT 2009


Hi Warren,

Warren Weckesser schrieb:
  > About the first error...
> 
> On Fri, Apr 17, 2009 at 4:14 AM, Christian K. <ckkart@hoc.net 
> <mailto:ckkart@hoc.net>> wrote:
> 
> 
>     Hi,
> 
>     I am having problems with the spline functions from
>     scipy.interpolate. Reading
>     the doc strings I expected the following to work:
> 
>     from scipy.interpolate import splev,splrep
>     import numpy as N
>     x = N.linspace(-4,10,5)
>     y = x**2
>     t,c,l = splrep(x,y,xb=0,xe=4)
> 
>     Traceback (most recent call last):
>      File
>     "C:\pythonxy\python\lib\site-packages\scipy\interpolate\fitpack.py",
>     line 406, in splrep
>        n,c,fp,ier = dfitpack.curfit(task, x, y, w, t, wrk, iwrk, xb, xe,
>     k, s)
>     error: (xb<=x[0]) failed for 1st keyword xb
> 
> 
> The error message is telling you what the problem is.  From the docstring:
> 
>     Given the set of data points (x[i], y[i]) determine a smooth spline
>     approximation of degree k on the interval xb <= x <= xe.
> 
> You have values in your x array outside the interval [xb,xe].

Right, but then I don't get the meaning of xb and xe at all. What sense 
does it make to choose a fit interval larger than the input data? IMHO 
x[0] < xb < xe < x[-1] should hold but obviously the docs tell the opposite.

Christian



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