Compiling GSL odeiv2 with g++ - gcc

Question

I'm attempting to compile the example code relating to the ODE solver, gsl/gsl_odeiv2, using g++. The code below is from their website :
http://www.gnu.org/software/gsl/manual/html_node/ODE-Example-programs.html
and compiles fine under gcc, but g++ throws the error
invalid conversion from 'void*' to 'int (*)(double, const double*, double*, double*,
void*)' [-fpermissive]
in the code :
#include <stdio.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_odeiv2.h>
int func (double t, const double y[], double f[], void *params)
{
double mu = *(double *)params;
f[0] = y[1];
f[1] = -y[0] - mu*y[1]*(y[0]*y[0] - 1);
return GSL_SUCCESS;
}
int * jac;
int main ()
{
double mu = 10;
gsl_odeiv2_system sys = {func, jac, 2, &mu};
gsl_odeiv2_driver * d = gsl_odeiv2_driver_alloc_y_new (&sys, gsl_odeiv2_step_rkf45, 1e-6, 1e-6, 0.0);
int i;
double t = 0.0, t1 = 100.0;
double y[2] = { 1.0, 0.0 };
for (i = 1; i <= 100; i++)
{
double ti = i * t1 / 100.0;
int status = gsl_odeiv2_driver_apply (d, &t, ti, y);
if (status != GSL_SUCCESS)
{
printf ("error, return value=%d\n", status);
break;
}
printf ("%.5e %.5e %.5e\n", t, y[0], y[1]);
}
gsl_odeiv2_driver_free (d);
return 0;
}
The error is given on the line
gsl_odeiv2_system sys = {func, jac, 2, &mu};
Any help in solving this issue would be fantastic. I'm hoping to include some stdlib elements, hence wanting to compile it as C++. Also, if I can get it to compile with g++-4.7, I could more easily multithread it using C++11's additions to the language. Thank you very much.

Answer 1

It looks like you have some problems with Jacobian. In your particular case you could just use NULL instead of jac in the definition of your system, i.e.
gsl_odeiv2_system sys = {func, NULL, 2, &mu};
In general you Jacobian must be a function with particular entries - see gsl manual - that is why your compiler is complaining.
Also, you may want to link the gsl library manually:
-L/usr/local/lib -lgsl
if you are on a linux system.