1. A computer implemented method for managing financial accounts by changing at least one control variable including at least one of a credit line and an annual percentage rate, the method comprising the steps of: collecting and storing in one or more storage devices account data for a plurality of financial accounts, where the account data are associated with a plurality of variables; establishing at least one control variable and at least one behavior variable based on the plurality of variables; determining by a data processor, a plurality of interval breakpoints for the at least one control variable and the at least one behavior variable; defining a plurality of account states based on the at least one control variable, the at least one behavior variable and the plurality of interval breakpoints; forming a transition matrix based at least in part on the account data and the plurality of account states; generating a Markov Decision Process (MDP) model based at least in part on the transition matrix; using the Markov Decision Process model to determine a change in the at least one control variable resulting in a desired effect on the plurality of account states; and changing at least one of the credit line and the annual percentage rate for the financial accounts based on the determined change.