Dear Omar, Monte Carlo method can be used to find a number and positions of Abrikosov vortices in a superconducting sample at the given magnetic field H. The number of vortices N allows one to obtain B, B=\Phi0*N/S, where \Phi0 is the flux quantum, S is the sample area perpendicular to H. The magnetization M is resulted as M= B/\mu0 - H, here \mu0 is the magnetic constant.