1. A computer-based method for aiding a user to validate a computer-based simulation model of the kind which simulates a multiple variable system using a suite of equations, comprising storing user-entered constraint knowledge defining (a) possible conditions of variables of the multiple variable system, the constraint knowledge being separate from the suite of equations, and (b) corresponding expected constraints on consequences of variables of the system, automatically applying the possible conditions of variables to the suite of equations to produce test consequences on variables of the system, and automatically analyzing the test consequences with respect to the constraints as an indication of the validity of the simulation model.