[Gsll-devel] Correction for integral-evaluate-spline

[Liam Healy]

GSL's  gsl_spline_ functions do exactly what you are looking for:
"remember" xarr and yarr so you don't have to keep sending them.
That's why they're missing from the arglist of
integral-evaluate-spline in GSLL.  The  gsl_interp_ functions require
the arrays, and that's why the GSLL equivalents take them as
arguments.

Please see and compare:
http://www.gnu.org/software/gsl/manual/html_node/Evaluation-of-Interpolating-Functions.html
double gsl_interp_eval_integ (const gsl_interp * interp, const double
xa[], const double ya[], double a, double b, gsl_interp_accel * acc)
which becomes #'intergral-evaluate-interpolation in GSLL
and
http://www.gnu.org/software/gsl/manual/html_node/Higher_002dlevel-Interface.html
Function: double gsl_spline_eval_integ (const gsl_spline * spline,
double a, double b, gsl_interp_accel * acc)
which becomes #'integral-evaluate-spline in GSLL.
They are two different functions with two different sets of arguments,
though they do the same thing.

Liam

On Tue, Jan 27, 2009 at 11:29 AM, Mirko Vukovic <mirko.vukovic at gmail.com> wrote:
> Hello,
>
> In order to use integral-evaluate-spline, I had to modify its
> definition.  The one below works, but I am not sure if there is a
> better way.  Here is the definition:
> (defmfun integral-evaluate-spline (spline xa ya low high acceleration)
>  "gsl_spline_eval_integ"
>  (((mpointer spline) :pointer) ((c-pointer xa) :pointer) ((c-pointer
> ya) :pointer) (low :double) (high :double)
>   ((mpointer acceleration) :pointer))
>  :c-return :double
>  :documentation                        ; FDL
>  "Find the numerical integral of an interpolated function over the
>   range [low, high], using the spline object spline,
>   data arrays xa and ya and the accelerator acceleration.")
>
> I removed a reference to a double-float `x' and added the x&y array
> pointers into the arguments, as they are necessary for gsl's
> `gsl_interp_eval_integ'.

They are needed for this function and they are there, in
integral-evaluate-interpolation.  You copied
and pasted the definition of integral-evaluate-spline, then put in
arguments that don't belong there.

> (I am really not sure what is the purpose of the ..._e functions).
>
> Here is a bit of test code that exercises the defintion by integrating
> pi*sin(pi x) between 0 & 0.5 which should equal 1.0:
>
> (let* ((acc (make-acceleration))
>       (xarr
>        (make-marray
>         'double-float
>         :initial-contents
>         (loop for i from 0.0d0 below 1d0 by 0.2d0
>            collect i)))
>       (yarr
>        (make-marray
>         'double-float
>         :initial-contents
>         (loop for x across (cl-array xarr)
>            collect (sin (* x pi)))))
>       (spline (make-spline *cubic-spline-interpolation* xarr yarr)))
>  (* pi (integral-evaluate-spline spline xarr yarr 0d0 0.5d0 acc)))
>
> I wonder if there is a way for `make-spline' to "remember" xarr and
> yarr so they don't have to be passed to `integral-evaluate-spline'.
>
> As always, thank for the heavy lifting :-)
>
> Mirko
>
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