void function(const alglib::real_1d_array &coeff, const alglib::real_1d_array &x, double &func, void *ptr)
{
   func =  coeff[0] / pow( 1 + coeff[1] * coeff[2] * x[0] , 1 / coeff[3] );
}

void main()
{

int N = 10;
int C = 4;
double epsx = 0.000001;
double diffstep = 0.0001;
alglib::lsfitstate state;
alglib::lsfitreport report;
alglib::ae_int_t maxits = 0;
alglib::ae_int_t info;

alglib::real_2d_array xAxis;
xAxis.setlength(N, 1);
alglib::real_1d_array yAxis;
yAxis.setlength(N);
alglib::real_1d_array cArray;
cArray.setlength(C);

/* Filling arrays  .... */

std::cout << " x " << xAxis.tostring(2) << std::endl; //printing xarray
std::cout << " y " << yAxis.tostring(2) << std::endl; // printing yarray
std::cout << " c " << cArray.tostring(10) << std::endl; //printing yarray

alglib::lsfitcreatef(xAxis,yAxis, cArray, diffstep, state);
alglib::lsfitsetcond(state, epsx, maxits);
alglib::lsfitfit(state, function);
lsfitresults(state, info, cArray, report);
std::cout << " Best fit coefficients " << cArray.tostring(12) << std::endl;
std::cout << " Informations  " << int(info) << std::endl;

}