MATLAB: C-Mex S function – storing values between timesteps

%scfunctionmexsimulink

Probably a noobish question…

For example, would it be possible to write a C mex S-function that returned the input value from three timesteps ago?

I ask this because I'd like to write a neural network as a C mex and would like weights etc to be stored between iterations.

Best regards,

Craig

Best Answer

You can create the discrete states in your s-function and save the input values in state variables in mdlupdate() function. You can output the values of these discrete variables (which are nothing but delayed values) in mdlOutput() function.

See this example for discrete state s-function.

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I would recommend looking at the documentation for mxCreateDoubleMatrix, particularly the examples listed at the bottom of the page, to understand how you can copy over your data into an mxArray.

However, I'm not sure why you'd want to call the PLOT command from within the S-function. Why not just mark your DWorks as discrete states using ssSetDWorkUsedAsDState and select the Save to Workspace options on the Data Import/Export pane of the Configuration Parameters dialog box - this will log the state values to the workspace at the end of simulation, at which point you can use the block's StopFcn callback to automatically plot the data at the end of simulation.

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The error messages indicate that the S-function code might not be in line with the level-1 C-MEX S-function template. An example is attached to this solution which shows a simple level-1 S-function. The level-1 C-MEX S-function template is also attached.

Note that MathWorks does not recommend creating new level-1 C-MEX S-functions, although compatibility for these still exists in current Simulink versions. It is recommended to use the level-2 C-MEX S-function interface whenever you create a new C-MEX S-function. The Level-1 S-function API is preserved only for backward compatibility with previous versions of Simulink.

In case of an issue with your existing level-1 C-MEX S-function you

might want to consider converting your S-function to a level 2 C-MEX S-function. For further information please type the following line into your MATLAB Command Window:

docsearch 'Converting Level 1 C MEX S-Functions to Level 2'

Best Answer

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