On explicit numerical schemes for the CIR process

In this paper we generalize an explicit numerical scheme for the CIR process that we have proposed before. The advantage of the new proposed scheme is that preserves positivity and is well posed for a (little bit) broader set of parameters among the positivity preserving schemes. The order of convergence is at least logarithmic in general and for a smaller set of parameters is at least $1/4$. Next we give a different explicit numerical scheme based on exact simulation and we use this idea to approximate the two factor CIR model. Finally, we give a second explicit numerical scheme for the two factor CIR model based on the idea of the second section.