I am trying to simulate a chomunnication scheme in simulink. I need to "construct" a non-linear function. I tryed the function block from Simulink>function>Fcn but seems that it doesnt coorporate well with if-clauses! Using the Matlab help I found that there is also an S- function that the user can implement his own model. However the help file doesn't say much. Can somebody help me with this S-function and how it works with the m-files???