MATLAB: Is it possible to create a triggered From Workspace block in Simulink 7.3 (R2010a)

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I would like to a From Workspace block that's able to reset its internal time when triggered. The block should work similarly to a repeating sequence that's controlled by an external execution signal and should obtain data from workspace.

Best Answer

The Simulink From Workspace block is not able to directly implement a triggering solution. This is due to the way this block is implemented in Simulink environment. When the model is initialized the variable is loaded from MATLAB workspace and the value can't be changed in runtime but only by stopping and starting the solver.

You can consider the following workaround based on Embedded MATLAB and a triggered subsystem. Please find the example model in Related Documents section.

The From Workspace has been replaced by a Constant block to obtain the full content of the workspace variable during initialization. Through a triggered subsystem the time when I should reset the input is calculated. This time difference is then used as an input to an Embedded MATLAB block that recreates the interpolation schema of the From Workspace block.

Please note that the Clock block is not allowed for code generation. You can consider substituting this block with a Digital Clock (with a fixed sample time) in case you need to generate code from your model.

Related Solutions

MATLAB: Do I receive an error when using Bus Objects in a Masked Subsystem in Simulink 6.0 (R14)

This bug has been fixed for Release 14 SP1 (R14SP1). For previous releases, please read below for any possible workarounds:

This has been verified as a bug in the way that bus objects are handled in Simulink 6.0 (R14) .

Currently, to work around this issue, you can remove the mask from the Subsystem or use the Bus Object as a Mask Parameter.

MATLAB: Does NLINFIT result in complex beta parameters in Statistics Toolbox 7.3 (R2010a)

NLINFIT does not produce complex parameter estimates if the x/y inputs and the function values return real inputs.

The most likely cause of the issue is that the model function is returning complex results for some inputs. If the function has been written by the user, he can put a check in the function if the result is real before returning. Another possibility is to edit the nlinfit.m file and add a check for real inputs to the checkFunVals subfunction. To edit the NLINFIT function:

1. Execute the following in the MATLAB command prompt:

edit nlinfit

2. Navigate to the chckFunVals function and add the following code to it:

% check if the function has real output
if any(~isreal(v))
      error('stats:nlinfit:NonRealFunOutput', ...
            'MODELFUN has returned complex values.');
end

One likely cause of the complex outputs of the function is that a positivity constraint must be enforced on one of the parameters. NLINFIT does not directly support such constraints. NLINFIT may try a negative value for the parameter, but if your model function takes a square root or another function that for a negative input returns a complex value, complex result is ensured. If that is the problem, a solution might be to reparameterize the problem using the log of that parameter, which will be unconstrained. Quite often, this is a better parameterization for positive parameters, as it makes the estimator closer to normal.

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Related Solutions

MATLAB: Do I receive an error when using Bus Objects in a Masked Subsystem in Simulink 6.0 (R14)

MATLAB: Does NLINFIT result in complex beta parameters in Statistics Toolbox 7.3 (R2010a)

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