Block callback function in Simulink model cannot access workspace variable when executed with parsim

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I have a Simulink model 'My Model', which uses a 'Check Static Range' block. In this block, assertion is enabled, and a callback function is defined. This function simply has the line of code
SatCount = SatCount+1;
The purpose is to count how many times a signal exceeds bounds.
The model is executed N times in parallel using parsim in wich all of the variables required to run the model are loaded in to the model workspace using code like the following
for p = 1:N
in(p) = Simulink.SimulationInput('My Model');
in(p) = in(p).setVariable('Var1',Var1,'Workspace','My Model');
in(p) = in(p).setVariable('Var2',Var2,'Workspace','My Model');
in(p) = in(p).setVariable('SatCount',0,'Workspace','My Model');
in(p) = in(p).setModelParameter('StopTime',1);
end
out = parsim(in,'ShowProgress', 'on');
When this is executed on a cluster machine using 12 workers, this fails and the following error messages are received
Error evaluating 'AssertionFcn' callback of Checks_SRange block (mask) 'My Model/Saturation Check'.
Callback string is 'evalin('base',callback)'
Caused by:
Unrecognized function or variable 'SatCount'.
I then tried moving the variable SatCount in to the base workspace using,
assignin('base','SatCount',0)
for p = 1:N
in(p) = Simulink.SimulationInput('My Model');
in(p) = in(p).setVariable('Var1',Var1,'Workspace','My Model');
in(p) = in(p).setVariable('Var2',Var2,'Workspace','My Model');
in(p) = in(p).setModelParameter('StopTime',1);
end
out = parsim(in,'ShowProgress', 'on');
But the same error message is received implying that the callback function cannot access the SatCount variable in either the base or model workspaces.
If I execute the same code above on my local workstation which does not have a Parallel Toolbox licence, the code executes correctly and the SatCount variable is updated, implying my local execution is using the base workspace to access SatCount.
Does anyone have an explaination as to why this does not run correctly with the Parallel Toobox?

Answers (3)

Rahul Kumar
Rahul Kumar on 11 Jan 2021
H David,
Variables specified on the SimulationInput object are not available in model or block callbacks. I would suggest using a PreSimFcn to set SatCount to zero before every simulation
in(p) = in(p).setPreSimFcn(@(~) assignin('base','SatCount', 0));
  2 Comments
Tong Zhao
Tong Zhao on 23 Apr 2022
Rahul: Actually you can grab values from SimulationInput object during PreSimFcn, by accessing the wanted SimulationInput object properties during the PreSimFcn call. This is a nice workaround that worked for me. For example:
function in = my_presimfun(in)
assignin('base','SatCount',in.Variables(1).Value);
end

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Nitin Kapgate
Nitin Kapgate on 13 Jan 2021
You can refer to a similar question answered here to resolve your issue. The issue described in this question is very similar to the one that is described in the link provided.

Paul
Paul on 22 Jan 2023 at 19:29
Edited: Paul on 23 Jan 2023 at 1:42
Hi David,
I think there is relatively straightforward solution to the original Question (I realize you found an alternative solution).
Basically, transfer variables from the base workspace of Matlab to the base workspace of the worker, run the simulation on the worker where the assertion callback updates the count variable in the base workspace of the worker, then use the PostSimFcn to pull the count variable from the base workspace of the worker into the simulation output.
For example, I have a simulation mysim that drives a Sine wave into a the Check Static Range block with the upper and lower bounds set to +0.5 and -0.5. The assertion callback is: SatCount = SatCount + 1.
Here is the code, run in an m-script.
clear
load_system('mysim')
simIn = Simulink.SimulationInput('mysim');
simIn = setVariable(simIn,'theGain',1); % this variable for a different part of the model. Ignore
simIn = setPostSimFcn(simIn, @(out) simpostfcn(out));
SatCount = 0; % initialize in the Matlab base workspace
out = parsim(simIn,'TransferBaseWorkspaceVariables','on');
function out = simpostfcn(out)
SatCount = evalin('base','SatCount'); % will eval in the base workspace of the worker if run with parsim
out.SatCount = SatCount; % add SatCount to the simulation output
end
After running this code SatCount in the Matlab workspace is unchanged
>> SatCount
SatCount =
0
However, the correct value lives in out (along with other simulation output as normal)
>> out
out =
Simulink.SimulationOutput:
tout: [63x1 double]
y: [1x1 timeseries]
SatCount: [1x1 double]
SimulationMetadata: [1x1 Simulink.SimulationMetadata]
ErrorMessage: [0x0 char]
>> out.SatCount
ans =
38
An altertanative is to use the preSimFcn suggested by @Rahul Kumar, which actually looks cleaner. My focus here was on how to get SatCount returned in the output of parsim.

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