From help-octave-request at bevo dot che dot wisc dot edu  Mon Nov  3 22:49:49 1997
Subject: Ack!  How to compute double integral?
From: jmr at everest dot radiology dot uiowa dot edu (Joe Reinhardt)
To: help-octave at bevo dot che dot wisc dot edu
Date: 03 Nov 1997 22:48:50 -0600

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I am trying to compute an M-dimensional integral using quad().   The
documentation says quad only does integration over a single variable,
so I tried nesting subroutine calls over each of my variables.

This method doesn't seem to work. 

I attached some sample code for 2-D showing that my technique fails.
The outer quad() call only evaluates one value of "y".

1) Is there a way to compute M-dimensional integrals in Octave?

2) I used global variables to pass parameters from integrand to
   integrand.   Is there a better way to do this?

Thanks!


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function ans = test(xmin, xmax, ymin, ymax)

  global xmin_g = xmin;
  global xmax_g = xmax;

  # compute area of unit circle	

  ans = quad("yint", ymin, ymax);

endfunction

function ans = yint(y)

  global xmin_g;
  global xmax_g;

  global y_g = y;

  printf("yint: y = %f\n", y);

  if (abs(y) <= 1)
    ans = quad("xint", xmin_g, xmax_g);
  else
    ans = 0;
  endif

endfunction

function ans = xint(x)

  global y_g;

  printf("xint: x = %f, y_g = %f\n", x, y_g);

  r = sqrt(x*x + y_g*y_g);

  if (r <= 1)
    ans = 1;
  else
    ans = 0;
  endif

endfunction


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-- 
Joe Reinhardt                            joe-reinhardt at uiowa dot edu
Department of Biomedical Engineering     1402 Engineering Building
University of Iowa                       Iowa City, IA 52242
Phone: 319-335-5634                      Fax: 319-335-5631

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