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[Bug-gsl] Cannot free vector after gsl_multimin_fdfminimizer_x call

From: Michael Braun
Subject: [Bug-gsl] Cannot free vector after gsl_multimin_fdfminimizer_x call
Date: Sun, 17 Apr 2011 19:09:47 -0400

Hi.  First off, thanks for all of the work you do with GSL.  It's certainly 
made my life much easier in a lot of areas.  But today I came across an error 
that for some reason I haven't seen before, even though I've used gsl_multimin 
quite a bit in the past.   It seems so simple, and so easy to replicate, that 
I'm sending it to the Bug list instead of Help.  I apologize in advance if that 
was the wrong decision.

Below this message I've pasted some code that should look rather familiar, 
since it is the example code from the GSL documentation (the functions from 
Section 36.4 and the example code in Section 36.9, both now in the same file).  
However, I have added or changed four lines of code, commented near the bottom 
of the file.  What I've done is allocated a new gsl_vector Y, assigned the 
current state of the minimizer to Y, pulled the current values of the minimizer 
from Y instead of from s->x, and then free Y.  So the only real change here is 
that I am using the gsl_multimin_fdfminimizer_x function to get the current 
state of s into a gsl vector, instead of pulling it directly from s->x.  

When I run this code, it prints the current state of the minimizer as expected 
(as you can see in this output).  The problem comes when trying to free Y.  The 
error is generated by the gsl_vector_free(Y) call.  I have no idea what I could 
be doing wrong here.

   1 4.99629 6.99072  687.84780
   2 4.98886 6.97215  683.55456
  11 2.19088 1.76182   45.31640
  12 0.86892 2.02622   30.18555
Minimum found at:
  13 1.00000 2.00000   30.00000
mmtest(17199) malloc: *** error for object 0xe: pointer being freed was not 
*** set a breakpoint in malloc_error_break to debug
Abort trap

My call to the compiler is 

gcc -lgsl -lgslcblas -o mmtest mmtest.c

and I get the same error with both gcc 4.2.1 and 4.6, as well as icc 12.0.0.  
This also happens using the C++ compilers (I was writing C++ code when it 

I am running the code on a Mac Pro running OSX 10.6.7.  This is GSL version 

Hopefully this is a helpful test example (just copy, paste and compile), and 
there is an easy fix.  Thanks, again, and here's the code from file mmtest.c :

#include <gsl/gsl_multimin.h>

double my_f (const gsl_vector *v, void *params)
 double x, y;
 double *p = (double *)params;

 x = gsl_vector_get(v, 0);
 y = gsl_vector_get(v, 1);

 return p[2] * (x - p[0]) * (x - p[0]) +
   p[3] * (y - p[1]) * (y - p[1]) + p[4]; 

void  my_df (const gsl_vector *v, void *params, 
      gsl_vector *df)
 double x, y;
 double *p = (double *)params;

 x = gsl_vector_get(v, 0);
 y = gsl_vector_get(v, 1);

 gsl_vector_set(df, 0, 2.0 * p[2] * (x - p[0]));
 gsl_vector_set(df, 1, 2.0 * p[3] * (y - p[1]));

void  my_fdf (const gsl_vector *x, void *params, 
        double *f, gsl_vector *df) 
 *f = my_f(x, params); 
 my_df(x, params, df);

int main (void)
 size_t iter = 0;
 int status;

 const gsl_multimin_fdfminimizer_type *T;
 gsl_multimin_fdfminimizer *s;

 double par[5] = { 1.0, 2.0, 10.0, 20.0, 30.0 };

 gsl_vector *x;
 gsl_multimin_function_fdf my_func;

 my_func.n = 2;
 my_func.f = my_f;
 my_func.df = my_df;
 my_func.fdf = my_fdf;
 my_func.params = par;

 x = gsl_vector_alloc (2);
 gsl_vector_set (x, 0, 5.0);
 gsl_vector_set (x, 1, 7.0);

 T = gsl_multimin_fdfminimizer_conjugate_fr;
 s = gsl_multimin_fdfminimizer_alloc (T, 2);

 gsl_multimin_fdfminimizer_set (s, &my_func, x, 0.01, 1e-4);

 gsl_vector * Y  = gsl_vector_alloc(2);  

     status = gsl_multimin_fdfminimizer_iterate (s);

     if (status)

     status = gsl_multimin_test_gradient (s->gradient, 1e-3);

     if (status == GSL_SUCCESS)
           printf ("Minimum found at:\n");

     Y = gsl_multimin_fdfminimizer_x(s);  

     // USING Y
     printf ("%5d %.5f %.5f %10.5f\n", (int)iter, gsl_vector_get(Y, 0), 
gsl_vector_get(Y, 1), s->f);

 while (status == GSL_CONTINUE && iter < 100);

 gsl_multimin_fdfminimizer_free (s);
 gsl_vector_free (x);


 return 0;

Michael Braun
Homer A. Burnell (1928) Career Development Professor, 
        and Assistant Professor of Management Science (Marketing Group)
MIT Sloan School of Management
100 Main St.., E62-535
Cambridge, MA 02139

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