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Re: [Help-gsl] Interpolated Values as function return

From: Foivos Diakogiannis
Subject: Re: [Help-gsl] Interpolated Values as function return
Date: Tue, 12 Nov 2013 05:26:26 +1100

(that awkward moment, when the shortcut apperas and sends an incomplete
email... APOLOGIES!)

Dear all,

This is not a sophisticated example (I am a humble astronomer, not a
software engineer) but may be of help to Klaus.

Say you have initiated interpolation at some point in your code, and you
wan't to use this interpolation as a function in ta numerical integration

// Define parameters for Function
struct gsl_params{
     gsl_spline * splineE; // Pointer to spline GSL definitions.
     gsl_interp_accel * accC; //accelerator for spline interpetation

// Degine kernel (function) that goes into the integration scheme.
double gsl_kernel(double r, void *p)
        gsl_params * params = reinterpret_cast<gsl_params * > (p);
        gsl_spline_eval (params->splineE, r, params->accC);

// Actual numerical integration function. Takes as argument the params
double gsl_integral( gsl_params * myparams){

        gsl_integration_workspace * w    = gsl_integration_workspace_alloc
        double result, error;

        gsl_function func { gsl_kernel, myparams}; // Function that is the
wrapper of the interpolation
        gsl_integration_qags (&func, 0, 1, 0, 1e-7, 1000, w, &result,

        gsl_integration_workspace_free (w);

        return result;

All the best, my deepest apologies for previous incomplete email.

On Tue, Nov 12, 2013 at 5:23 AM, Foivos Diakogiannis <
address@hidden> wrote:

> On Tue, Nov 12, 2013 at 5:04 AM, Rhys Ulerich <address@hidden>wrote:
>> > But searching the internet told me, that it is not possible to get the
>> > address from a member function in C++!?
>> I believe that's true but have never looked in-depth, however,...
>> > have to give the GSL function the address of the member
>> > function, in that case the foo::operator()().
>> I'm suggesting storing a pointer to an instance in
>> gsl_function.params.  Then, in the function, retrieving that pointer,
>> casting it to the object type, and calling a method on the instance.
>> > Uh, what do you mean with 'it definitly _does not_complie'? So my idea
>> is
>> > plain wrong?
>> Not at all.  Just that my sample code wouldn't build.
>> - Rhys

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