Re: [R] How to get correct integration in C for step function?

From: Sundar Dorai-Raj <sundar.dorai-raj_at_pdf.com>
Date: Mon 22 Jan 2007 - 01:26:22 GMT

Hi, Lynette,

A few pointers:

  1. Not an R question.
  2. Not an ESS question.
  3. No reproducible example.
  4. (x >= 1/4) is comparing a pointer. Surely, this is not what you intended to do. Plus, if you're using void* then this is not even a C function called by R. And I'm not familiar with Rdqags.
  5. Please use the posting guide in the future.

http://www.R-project.org/posting-guide.html

HTH, --sundar

Lynette said the following on 1/21/2007 5:24 PM:
> Dear all,
>
> I am using Rdqags in C to realize the integration. It seems for the
> continous C function I can get correct results. However, for step functions,
> the results are not correct. For example, the following one, when integrated
> from 0 to 1 gives 1 instead of the correct 1.5
>
> void func( double *x, int n, void *ex )
> {
> int i;
>
> for(i=0;i<n;i++) { x[i]=( ((x>=1/4)&&(x<=3/4)) ? 2:1 ) ; }
> return;
> }
>
> while the following one when integrated from 0 to 1 gives the correct
> 0.7853983
>
> void func( double *x, int n, void *ex )
> {
> int i;
>
> for(i=0;i<n;i++) { x[i]= pow(1-x[i]*x[i],.5); }
> return;
> }
>
> Please advise the problems. Thanks a lot.
>
> Best,
> Lynette
>
> ______________________________________________
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> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon Jan 22 12:31:57 2007

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