[Bug-gsl] Interpolation

[Евгений Курбатов]

Dear Brian

I like GSL very much and I'm using it widely but..
why the interpolating routines become extrapolating sometimes?  Today I spent 
several hours to find the stupid bug in my program due to interpolation bounds 
violation.  When an interpolation point becomes greater than right bound or 
lower than left then no error returns but the routine extrapolates a function 
value to that point giving very brave values.  Only observing of sources showed 
this is the feature, not the bug.
Would it be better to introduce some flags for gsl_interp_init or somewhere 
indicating the needing for bounds check.  This check can be done in a one line 
(e.g. line 277 of cspline.c).  Or just hardcode this checkup without a flags.  
Or at least note this feature in a manual.

Thank you Brian.

Regards,
Evgeny Kurbatov