Re: [R] use "integrate" for functions defined in C, not R

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Tue 10 May 2005 - 14:51:25 EST

On Mon, 9 May 2005, Zhijin Wu wrote:

> Dear all,
> I am trying to use the C code for "integrate" function ( that calls
> Rdqagi and Rdqags) so that I can integrate a function defined in C,
> instead of passing from R.
> Is there a way for doing this?
>
> My unsuccessful attempt:
> I looked into the files (including integrate.c, Applic.h) and
> 1. modified the definition of
> "integr_fn" by droping the environment "*ex",
> void integr_fn(double *x, int n)
> and dropped all use of "ex" used in the code
>
> 2. defined my checker function f1 and the vectorizing function "Cintfn" in
> place of "Rintfn"
>
> double f1(double x){ return(x);}
> static void Cintfn(double *x, int n)
> {
> int i;
> for(i = 0; i < n; i++)
> x[i] = f1(x[i]);
> return;
> }
>
> 3. Similar to "call_dqags", I define a C function "my_call_dqags" that
> has it's own parameters of "lower, upper" and etc define in C, instead of
> parsing from R. And I call
> Rdqags(Cintfn,
> &lower, &upper, &epsabs, &epsrel, &result,
> &abserr, &neval, &ier, &limit, &lenw, &last, iwork, work);
> instead of
> Rdqags(Rintfn, (void*)&is,
> &lower, &upper, &epsabs, &epsrel, &result,
> &abserr, &neval, &ier, &limit, &lenw, &last, iwork, work);
>
> I am not passing (void*)&is because I no longer have the "environment".
>
> The code compiles fine with R CMD SHLIB. But it returns 5.3e-317 for my
> checker function f(x)=x, integration interval (1,2).
>
> Thanks for any hint!

  1. This is the wrong list: please read the posting guide.
  2. You cannot just leave out arguments in C calls, so it seems that you need help with C programming rather than R. If you include the appropriate headers this will be checked, so I guess you have not.
-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Tue May 10 14:55:58 2005

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