In this thesis the Conjugate Gradient method used in the forecasting of the number of students in the Netherlands is investigated. The addition of international students to the forecasting led to mathematical problem of which a solution could not be computed. While the numerical method is working as intended, the work presented in this thesis shows that the unsolvability lies with a linear system that has no solution. The cause of this is attributed to the use of a selection process in the linear system. Leading to a hugely singular matrix and a forecasting problem without a solution. Several methods were tried to change the use of the selection process but without any results .