Re: GSL-1.2 gsl_eigen_symmv() Problem

[Adam Johansen <amj26@hermes.cam.ac.uk>]

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Hello Again,

Further to my earlier email, I've managed to narrow the problem down
somewhat. It would seem that if the log() function is called before a call
to gsl_eigen_symmmv with a matrix similar to one which has already been
solved (this is a rough summary which may not be entirely accurate, but I
think contains the relevant details) then that routine goes into an
apparently infinite loop.

I've attached a short piece of code which demonstrates this problem and
I'd be interested to know whether it is a general one or is confined to
systems like my own (or indeed, is due to a corrupt library and is only
happening to me...).

Many apologies if this is a known problem, or if there's some obvious
reason why using the C libraries log function in conjunction with gsl
isn't a reasonable thing to do....

Adam Johansen



[-- Attachment #2: The offending code --]
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#include <stdio.h>

#include <gsl/gsl_eigen.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_vector.h>

int main(int argc, char** argv) {
  double hmmm;
  gsl_eigen_symmv_workspace* wsp;
  gsl_matrix* in, *out;
  gsl_vector* vec;

  in = gsl_matrix_alloc(2,2);
  out = gsl_matrix_alloc(2,2);
  vec = gsl_vector_alloc(2);
  int i;

  int mi = 0;

  for(i = 1; i < 101; i++) { 
     hmmm = log(1.2);
     
     for(mi = 0; mi < 6; mi++) {
	wsp = gsl_eigen_symmv_alloc(2);
       
	gsl_matrix_set(in, 0, 0, i);
	gsl_matrix_set(in, 0, 1, i - 1);
	gsl_matrix_set(in, 1, 0, i - 1);
	gsl_matrix_set(in, 1, 1, i - 0.5);
	
	printf("Solving matrix %i in iteration %i...\n", mi, i);
	gsl_eigen_symmv(in, vec, out, wsp);
	
	gsl_eigen_symmv_free(wsp);
     }
  }
}