odeint streaming observer and related questions

Question

I have a system of 4 coupled equations to solve and a parameter Gamma[i] to iterate over. Since I am quite new to C++, my code is a very rudimentary. If it looks sophisticat

Answer 1

Question #1 :

I do not understand exactly what kind of output you need. But if you want to write the result after each iteration you can implement an output observer like this:

struct output_observer
{
    string filename_;
    size_t count_;
    output_observer( const string &filename ) : filename_( filename ) , count_( 0 ) { }
    void operator()( const state_type &x , time_type dt )
    {
        char fn[512] = "";
        sprintf( fn , "%s_%04lu.csv" , filename_.c_str() , count_ );
        ofstream fout( fn );
        for( size_t i=0 ; i

You can apply this observer simply by

integrate_const( runge_kutta4< vector >() , nli_obj , x ,
    0.0 , 3.0 , dz , output_observer( "filename" ) );

Is this the desired functionality?

Question #2 :

It is not possible to see the intermediate e steps of runge_kutta4. The coefficients are the standard ones for the classical Runge-Kutta method: http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods

Question #3 :

odeint has several error steppers, which estimate the error made during one step. You can use for example the Runge_Kutta Cash Karp algorithm;

runge_kutta_cash_karp54< state_type > rk;
state_type xerr;
rk.do_step( nli_obj , x , t , xerr );

which makes ONE step and estimates the error and writes the error result in xerr.