[Help-gsl] setting function of gsl_odeiv_system structure to a C++ class member function

[Luke]

I am trying to create a C++ class to organize the various functions I have
generated for my system.  Here is my class definition:

class
Torus

{


private:


    const gsl_odeiv_step_type *
T;

    gsl_odeiv_step *
s;

    gsl_odeiv_control *
c;

    gsl_odeiv_evolve *
e;

    gsl_odeiv_system sys;
  public:



Torus();


~Torus();

    int eoms(double t, const double x[8], double f[8], void *params);
};


Then, in the constructor, I have:

Torus::Torus()

{

  t =
0.0;

  T =
gsl_odeiv_step_rk8pd;

  s = gsl_odeiv_step_alloc(T,
8);

  c = gsl_odeiv_control_y_new(1e-6,
0.0);

  e = gsl_odeiv_evolve_alloc(8);
  // Can't get the following to work:


  //sys = {eoms, NULL, 8, NULL};  // doesn't work
  sys.function = &eoms; // doesn't work
  sys.function = eoms; // doesn't work
  sys.function = this.eoms; // doesn't work
  sys.function = Torus::eoms; // doesn't work
  sys.jacobian = NULL; // works
  sys.dimension = 8; // works


  sys.params= NULL;  // works


}

right now, I just have a stub for my eoms function:

int Torus::eoms(double t, const double x[8], double f[8], void *params)
{
  return GSL_SUCCESS;
}

Here are the errors I have receive when I try to compile (g++ -Wall -lgsl -c
torus.cpp):
With sys.function = &eoms;  :
torus.cpp: In constructor ‘Torus::Torus()’:
torus.cpp:12: error: ISO C++ forbids taking the address of an unqualified or
parenthesized non-static member function to form a pointer to member
function.  Say ‘&Torus::eoms’
torus.cpp:12: error: cannot convert ‘int (Torus::*)(double, const double*,
double*, void*)’ to ‘int (*)(double, const double*, double*, void*)’ in
assignment

With sys.function = eoms; :
torus.cpp: In constructor ‘Torus::Torus()’:
torus.cpp:12: error: argument of type ‘int (Torus::)(double, const double*,
double*, void*)’ does not match ‘int (*)(double, const double*, double*,
void*)’

With sys.function = this.eoms;
torus.cpp: In constructor ‘Torus::Torus()’:
torus.cpp:12: error: request for member ‘eoms’ in ‘this’, which is of
non-class type ‘Torus* const’

With sys.function = this->eoms;
torus.cpp: In constructor ‘Torus::Torus()’:
torus.cpp:12: error: argument of type ‘int (Torus::)(double, const double*,
double*, void*)’ does not match ‘int (*)(double, const double*, double*,
void*)’

With sys.function = &Torus::eoms;
torus.cpp: In constructor ‘Torus::Torus()’:
torus.cpp:12: error: cannot convert ‘int (Torus::*)(double, const double*,
double*, void*)’ to ‘int (*)(double, const double*, double*, void*)’ in
assignment

Is there something simple that I haven't tried to get this assignment to
work?  Or is there a different way I should be doing it?

Thanks,
~Luke Peterson