error when using lsqnonlin with 'levenberg-marquardt' algorithm

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Kukhokuhle Tsengwa
Kukhokuhle Tsengwa on 6 May 2021
When using lsqnonlin, I am getting the error:
  1. Derivative of state '1' in block 'armDynamics/Integrator' at time 1.9771760646058036 is not finite. The simulation will be stopped. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)
I have set:
options = optimoptions(@lsqnonlin, 'Algorithm','levenberg-marquardt', 'Display','off','StepTolerance',0.001,'OptimalityTolerance',0.001);
Any assistance would be appreciated.

Answers (1)

Shiva Kalyan Diwakaruni
Shiva Kalyan Diwakaruni on 12 May 2021
Hi,
This problem occurs when an integrator is present in the model.
Open Configuration Parameter, set the diagnostic "Inf or NaN block output" to error, you will get the error as follows:
An error occurred while running the simulation and the simulation was terminated
Caused by:
  • Block 'BlockName' outputs 'NaN' for element x of output port x at major time step 0 where BlockName is the block in which error is thrown.
This blocks has a divide by zero, which creates a Inf that when fed to an Integrator, generates this error.
So, avoid division by zero in the logic.
Hope it helps.

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