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questions about the 'pdeeig'

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Haya M
Haya M on 24 Jan 2020
Edited: Ravi Kumar on 28 Jan 2020
I'm using the syntax [?,?]=??????(?,?,?,?.1.0,?,1.0,[−1,1]); to solve a PDE on a given domain with a given ? ,
I have two questions about this syntax
How can I extract the matrices of the finite elements system for the PDE i.e ?
how I can assure that the computed eigenvalue say ?(2) corresponds to the correct eigenfunction ?(:,2)? I mean are they eigenpairs? is there any way to check that?


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Accepted Answer

Ravi Kumar
Ravi Kumar on 24 Jan 2020
Edited: Ravi Kumar on 27 Jan 2020
Please use one the newer workflow like general equation based one, Structural or Thermal one. Once you setup your model in one of the newwer workflow you can get matrices using assembleFEMatrices function.
For your second question you can back substitute eigenpair into the equation and make sure the residual is near zero.


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Ravi Kumar
Ravi Kumar on 27 Jan 2020
Knowing v1 and l1, you can compute the residual as:
res = norm(K*v1-l1*v1), this would be close to zero only if l1 and v1 are the right pair.
PS: I fixed typo in my previous comment.
Haya M
Haya M on 28 Jan 2020
Thank you Ravi for the answer,
Do you mean that res = norm((K-l1)*v) ?
best regards,
Ravi Kumar
Ravi Kumar on 28 Jan 2020
Yep, that's right. Fixed my comment again.

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