pass parameter to boost integrator - c++

Question

I have read these answers 1, 2 about passing parameter to odeint (Boost).
I tried here to do the same process. but the code give wrong answer.
Here is my try:
This is simplified code of boost calculation of lyapunov exponent of Lorenz oscillator.
#include <iostream>
#include <boost/array.hpp>
#include <boost/numeric/odeint.hpp>
#include "gram_schmidt.hpp"
using namespace std;
using namespace boost::numeric::odeint;
typedef vector<double> dim1;
const double sigma = 10.0;
const double R = 28.0;
const double b = 8.0 / 3.0;
const size_t n = 3;
const size_t num_of_lyap = 3;
const size_t N = n + n * num_of_lyap;
// system with out perturbation
struct lorenz
{
void operator()( const dim1 &x , dim1 &dxdt , double t ) const
{
dxdt[0] = sigma * ( x[1] - x[0] );
dxdt[1] = R * x[0] - x[1] - x[0] * x[2];
dxdt[2] = -b * x[2] + x[0] * x[1];
}
};
// system with perturbation
void lorenz_with_lyap( const dim1 &x , dim1 &dxdt , double t )
{
lorenz()( x , dxdt , t );
for( int l=0 ; l<num_of_lyap ; ++l )
{
const double *pert = &x[3 + l * 3];
double *dpert = &dxdt[3 + l * 3];
dpert[0] = - sigma * pert[0] + 10.0 * pert[1];
dpert[1] = ( R - x[2] ) * pert[0] - pert[1] - x[0] * pert[2];
dpert[2] = x[1] * pert[0] + x[0] * pert[1] - b * pert[2];
}
}
//------------------------------------------------------------------------
int main( int argc , char **argv )
{
const double dt = 0.01;
dim1 x(N);
x[0] = 10.; x[1] = 10.0; x[2] = 5.0; // initial condition
dim1 lyap(3);
runge_kutta4<dim1, double, dim1, double, range_algebra> rk4;
// perform 10000 transient steps
integrate_n_steps(rk4, lorenz(), x, 0.0, dt, 10000);
fill( x.begin()+n , x.end() , 0.0 );
for( size_t i=0 ; i<num_of_lyap ; ++i ) x[n+n*i+i] = 1.0;
fill( lyap.begin() , lyap.end() , 0.0 );
double t = 0.0;
size_t count = 0;
while( true )
{
t = integrate_n_steps( rk4 , lorenz_with_lyap , x , t , dt , 100 );
gram_schmidt< num_of_lyap >( x , lyap , n );
++count;
if( !(count % 1000) )
{
cout << t;
for( size_t i=0 ; i<num_of_lyap ; ++i ) cout << "\t" << lyap[i] / t ;
cout << endl;
}
}
return 0;
}
first I defined these classes
class lorenz
{
public:
void operator()...
and
class lorenz_with_lyap
{
public:
void operator()(const dim1 &x, dim1 &dxdt, double t) const
{
dxdt[0] = sigma * (x[1] - x[0]);
dxdt[1] = R * x[0] - x[1] - x[0] * x[2];
dxdt[2] = -b * x[2] + x[0] * x[1];
for (int l = 0; l < num_of_lyap; ++l)
{
const double *pert = &x[3 + l * 3];
double *dpert = &dxdt[3 + l * 3];
dpert[0] = -sigma * pert[0] + sigma * pert[1];
dpert[1] = (R - x[2]) * pert[0] - pert[1] - x[0] * pert[2];
dpert[2] = x[1] * pert[0] + x[0] * pert[1] - b * pert[2];
}
}
};
then I can change it a little to define a parameter:
class lorenz
{
double sigma;
public:
lorenz(double si) : sigma(si) { }
void operator()...
but defining the lorenz_with_lyap class change the result, and I don't know where I am doing something wrong.
Do you have any idea?
(This is now a homework and I am going to check the result of this code with another method).
Thank you.

Answer 1

After some struggling, I finally corrected that, post it here if somebody probably is interested:
class lorenz
{
public:
void operator()(const dim1 &x, dim1 &dxdt, double t) const
{
dxdt[0] = sigma * (x[1] - x[0]);
dxdt[1] = R * x[0] - x[1] - x[0] * x[2];
dxdt[2] = -b * x[2] + x[0] * x[1];
}
};
class lorenz_with_lyap
{
const double sig;
public:
lorenz_with_lyap(double si) : sig(si) { }
void operator()(const dim1 &x, dim1 &dxdt, double t) const
{
dxdt[0] = sig * (x[1] - x[0]);
dxdt[1] = R * x[0] - x[1] - x[0] * x[2];
dxdt[2] = -b * x[2] + x[0] * x[1];
for (int l = 0; l < num_of_lyap; ++l)
{
const double *pert = &x[3 + l * 3];
double *dpert = &dxdt[3 + l * 3];
dpert[0] = -sig * pert[0] + 10.0 * pert[1];
dpert[1] = (R - x[2]) * pert[0] - pert[1] - x[0] * pert[2];
dpert[2] = x[1] * pert[0] + x[0] * pert[1] - b * pert[2];
}
}
};
//------------------------------------------------------------------------
// in main
lorenz_with_lyap lo(10.0);
t = integrate_n_steps(rk4, lo, x, t, dt, 100);
...