MATLAB: Passing information between level-2 matlab s-functions

Question

I am trying to model a two step chemical process using simulink and s function for each step. 5 outputs from step 1 are connected to the 5 inputs of step 2. I initialize the outputs of step 1 in its s function using read in parameters. When I initialize the state variables of step 2, which uses outputs from step 1, the values of the output the output variables of step 1 inside step 2 initialization are zero. What can I do to fix this?

Thanks. Girish

Answer 1

Some background info that you may find useful...

- Simulink goes through an "initialization" phase prior to starting its simulation loop. Here it will call certain S-function methods for each block, such as the method that will initialize the state variables (for MATLAB S-functions, I believe this is the InitializeConditions block method).

- During the simulation loop, Simulink typically first computes all block outputs, then it will go back and compute updates to state values. This is the typical "Output" and "Update" functions.

One key thing to note is that the initialization part comes prior to any block outputs being produced. On that note, it sounds based on your description that you are trying to use a block input value during the initialization phase of the simulation. This is not going to work for you.

Each block must set its own initial state values based on initial conditions. You could use some MATLAB code outside of the S-functions to pass the correct initial values to each, if that is necessary.