1. A method for analyzing the behavior of complex systems, particularly internal combustion engines, by calculating a model which represents various measured variables of the function of input variables, having the following basic steps: selecting various measured points which correspond to different constellations of measured variables and performing measurements to ascertain measured variables on a real system; preparing a model which simulates the dependence of the measured variables on the input variables and calibrating the model on the basis of the measured values of the real system obtained at the measured points; characterized in that the following steps are specifically performed: subdividing the model into at least two partial models; preparing at least one first partial model which simulates a first partial set of the measured variables; identifying at least one first main influence parameter for the first partial model; determining an optimum value of the first main influence parameter in each measured point; interpolating the first main influence parameter for all meaningful constellations of input variables to calibrate the first partial model; preparing a further partial model to simulate a further partial set of the measured variables as a function of input variables and the previously ascertained first partial set of the measured variables; identifying at least one further main influence parameter for the further partial model; determining an optimum value of the further main influence parameter in each measured point; interpolating the further main influence parameter for all meaningful constellations of input variables to calibrate the further partial model.