Improve efficiency of AssembleFEMatrices?

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Dear all,
I am using the PDE Toolbox to perform a FEM simulation. I am using the following toolbox function to aquire the matrices I am after:
FEM = assembleFEMatrices(model,'nullspace')
However, the only matrices I require are the global stiffness matrix (FEM.Kc) and nodal force vector (FEM.Fc).
The issue is that the assembleFEMatrices function is quite costly. I was wondering if there is a way improve the efficiency of this? Could the stiffness matrix and force vector be calculated another way, i.e. could they be calculated from the results of the 'solve' function that is less time consuming:
results = solve(model);
Or if it is possible to assemble ONLY the matrices you desire to reduce the computational expense?
Thank you for any advices/solutions that can be offered

Risposta accettata

Ravi Kumar
Ravi Kumar il 30 Mar 2021
If you are using R2020b or newer version of MATLAB, you should be able to specify required matrices as input:
Regards,
Ravi
  3 Commenti
Elliot Bontoft
Elliot Bontoft il 31 Mar 2021
Hi all,
Ravi was right and this was possible through using specified requested matrices in the input. You just have to manually impose the boundary conditions to build the stiffness matrix and force vector, as follows:
FEM = assembleFEMatrices(model,'HKAQFG');
[FEM.B,Or] = pdenullorth(FEM.H); % compute the nullspace of columns of H
FEM_Fc = FEM.B'*(FEM.F + FEM.G);
FEM_Kc = FEM.B'*(FEM.K + FEM.A + FEM.Q)*FEM.B;
This is notably faster than using
FEM = assembleFEMatrices(model,'nullspace')
to access the FEM.Fc and FEM.Kc matrices
Ravi Kumar
Ravi Kumar il 31 Mar 2021
Eaxctly! Selecting a subset of matrices or specifying BC appliction option are sort of orthogonal. You need to do the way you are doing. I would also add, you can assemble some of these matrices once and some that have some variation over time or solution repeatedly.

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