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Why am I getting a wrong matrix inverse when using a Math Function block set to 'pow' in Simulink?

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I want to calculate a matrix inverse in Simulink. For example, for matrix A = [4 0; 0 16]. I am using a Math Function block set to 'pow' to do the inverse. However, I get erroneous result as below:
A^-1 = [0.25 inf; inf 0.0625]
rather than
A^-1 = [0.25 0; 0 0.0625]

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 15 Dec 2017
Using the Math Function block set to 'pow' to do the inverse operation does the element-wise inverse rather than inverting the whole matrix. To carry out a matrix inverse, please follow the steps below:
  1. Add a Product block into the model
  2. Double click on the block
  3. Under 'Number of inputs' section replace the number '2' with the right-matrix division symbol ' / '
  4. Select 'Multiplication' as 'Matrix(*)'
This will return the matrix inverse.


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