Variable size signal for integrator in Simulink

In my model (simplified version is shown below), the output size of matlab function is determined by the input. I changed the output size to "Variable size" with the upper and lower limits. Without the integrator the model works, but when I add integrator to the output of function I get this error:

"Simulink cannot propagate the variable-size mode from the output port 1 of 'untitled/MATLAB Function' to the input port 1 of 'untitled/Integrator'. This input port expects a fixed-size mode. The variable-size mode originates from 'untitled/MATLAB Function'. Examine the configurations of 'untitled/Integrator' 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."

I know the variable-size signal is not supported by the integrator block. I am wondering if there is any solution to this issue?

function y = fcn(u)

y = ones(u,1);

[Paolo Mastracci]

Have you solved this problem? I'm experiencing the same issue

[Leila Farahani]

Have you solved this problem? I'm experiencing the same issue too

Answer 1

[Rajanya]

Hi @Sam136,

I understand that you are passing a variable size input to the integrator block and therefore, Simulink throws the error saying that either the block does not support variable size inputs or needs to be configured for them.

I would like to add a point here that if the block can work for variable size inputs, it can be configured by going to the ‘Explore’ section of the MATLAB function block and checking the ‘variable size’ checkbox with minimum and maximum value bounds.

However, one of the block characteristics of the integrator block is that it currently does not support inputs from variable size signals.

A workaround could be to use ‘Selector’ or ‘Switch’ logic to select the portions of the signals which are necessary at a given time, ensuring the input to the integrator always stays fixed size. You can also make use of ‘Buffers’ to make them store values and process them in batches of fixed size.

Refer to this documentation on integrator block characteristics - https://www.mathworks.com/help/simulink/slref/integrator.html?searchHighlight=integrator%20simulink&s_tid=srchtitle_support_results_2_integrator%20simulink#f7-890704_blockchar

Hope this helps.

Answer 2

[Walter Roberson]

Use an iterator subsystem to loop over the vector elements, integrating one by one.

https://www.mathworks.com/help/ecoder/ug/for-loop.html