A numerical modeling algorithm is developed which is able to calculate the powers of an arbitrary number of heaters in a crystal growth configuration in order to obtain a prescribed temperature distribution in a growing crystal. Such a mathematical procedure is called inverse modeling. The algorithm is implemented in our software system Crys-VUN++ for global thermal simulation of crystal growth processes. The efficiency of this new strategy of inverse modeling is demonstrated by applying it to an industrial vertical gradient freeze (VGF) process for the growth of GaAs crystals with 3 " diameter. As a result we obtain optimized growth conditions which will be discussed in comparison to the state of the art of VGF technology.