Hi Nayla - the value for initial position state target needs to be a hard coded value or a MATLAB variable. It cannot be set by another block in your model. That initial value specifies the requested initial angle of that joint, but that needs to be checked against other states in the mechanism to ensure that angle can be achieved.
If you can use your MATLAB function to calculate that angle outside of the simulation and then enter that value as the target, then you have that function calculate the initial target value.
--Steve
