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Re: Double integration results in "error: quad: invalid recursive call"


From: Geordie McBain
Subject: Re: Double integration results in "error: quad: invalid recursive call"
Date: Thu, 24 Feb 2005 10:34:17 -0500
User-agent: Mutt/1.5.6+20040907i

No, I don't know whether you can call quad recursively; however, there
is another way to compute integrals over rectangles in Octave: use
Gaussian quadrature via colloc().  In your example, define

  function z = f (x,y)
    z = x * y;
  endfunction

then:

  octave> n=1; [r, A, B, q] = colloc (n); r*=10; r+=0; q*=10; q'*f(r,r')*q
  ans = 2500

(which is exact, since the integrand is linear in each of its two
variables; use a bigger n otherwise).

Geordie McBain
www.aeromech.usyd.edu.au/~mcbain

On Wed, Feb 23, 2005 at 04:26:13AM -0600, Timo Steffens wrote:
> Hello,
> 
> I am trying to compute a double integration with octave. Since I am 
> migrating from "Mathematica", maybe I am thinking wrong. In Mathematica I'd 
> do
> NIntegrate[NIntegrate[d1*d2, {d1, 0, 10}], {d2, 0, 10}]
> 
> 
> 
> In Octave I tried the following:
> 
> >>function y = myfunc(d1)
> y=d1*d2
> endfunction
> >>function y = firstint(d2)
> [y,ier,nfun,err] = quad('myfunc',0,10)
> endfunction
> >>[result,ier,nfun,err] = quad('firstint',0,10)
> error: quad: invalid recursive call
> error: called from `firstint'
> error: quad: evaluation of user-supplied function failed
> 
> 
> 
> I am using version 2.1.50 for windows. I read in the archives that the 
> error for calling quad more than once has been fixed in 2.0.16
> 
> I couldn't find information about this behavior in the documentation or the 
> mailing list archives...So is it a bug or am I doing something wrong?
> 
> 
> 
> Thanks!
> Timo Steffens
> ----------------------------------------------
> Doctorate Programme Cognitive Science
> Kolpingstr. 7 - Room 01/209 - 49074 Osnabruck
> http://www.cogsci.uos.de/~tsteffen
> phone: +49(0)541/969-4065
> ----------------------------------------------
> 
> 
> 
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Octave is freely available under the terms of the GNU GPL.

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