Re: [Help-gsl] cspline: gsl_spline_eval

[Rhys Ulerich]

> Hi, i upgraded from openSuse 11.3 to 12.1 and got a new gsl version....
>
> But now i'm getting always error messages "interp.c:150: ERROR: interpolation 
> error". I think it's because i want y values for x
> values lower/bigger than the x values in my interpolation points. How can i 
> get these values? I don't want to add additional
> interpolation points because that will change my spline.

Changed in http://bzr.savannah.gnu.org/lh/gsl/trunk/revision/4704.

Judging from the line
   GSL_ERROR_VAL("interpolation error", GSL_EDOM, GSL_NAN);
within interp.c, I don't think you can get the older, extrapolating behavior.

The related mailing list thread discussing the change was here:
http://lists.gnu.org/archive/html/bug-gsl/2010-11/msg00010.html

Your options seem to be:
1) Don't extrapolate.
2) Hack your local version of the code to remove the extrapolation check.
3) Use some basic facts about splines to write an
extrapolation-friendly version which defers to the library version.

Sorry,
Rhys