[petsc-users] Lengthy time to assemble the matrix

[Li, Zhisong (lizs)]

 Hi, Petsc Team,

I noticed that the Petsc program often cost a lot of time to assemble a matrix, particularly when DOF is large. For example, I write a 3D structured CFD code with a linear system of 40 x 22 x 20 in dimension and DOF = 6. In a sequential computation, it takes more than 20 minutes to finish assembling the matrix before ksp operates. This same problem should take only a few seconds for a commercial CFD software to initialize.

The processor is 2.67G Hz in speed with sufficient RAM (6GB). The largest matrix stencil is 19 points. I typically use the function: MatSetValuesStencil(A, 1, &abc, 19, def, val, INSERT_VALUES). I wonder the assembling can be faster if abc is an array of multiple matrix row coordinates. But in the case of DOF >1, this seems difficult to implement.

Is this normal for Petsc or do we have any means to improve this?


Thank you.


Zhisong Li
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