MATLAB: Simulink – Programmatically Set Vector Sizes at Run Time

Question

I'm trying to run a model where the length of the vector (N_lag) changes each time I run "sim test2.slx".

for i = 1:M;

N_lag = N_lag + 1;

sim test2.slx;

end

Simulink gives me this after I accept its suggestion to name the vector (y) as a variable size vector with size [N_lag,1].

"Simulink cannot propagate the variable-size mode from the output port 1 of 'test2/Add' to the input port 1 of 'test2/Memory'. This input port expects a fixed-size mode. The variable-size mode originates from 'test2/MATLAB Function'. Examine the configurations of 'test2/Memory' for one of the following scenarios: 1) the block does not support variable-size signals; 2) the block supports variable-size signals but needs to be configured for them."

The problem is, I can't seem to find any type of block that will let me do this (global variable data stores also can't have variable size data). I'm trying to run the model a few thousand times, so hard coding the length of the vector is not an option.

The simplified block diagram is shown below.

Suggestions?

Thanks!

Answer 1

I think I hacked a solution for those who are also interested in this. I basically allocated a fixed length, maximum memory vector (length N_max) for the memory block and a variable length vector for the data processing. Then I glued them together using converter functions that simply write/read 1:N_lag entries of the memory vector, leaving the rest of them alone so that the memory block only sees a fixed length data stream. Seems to work pretty well so far.