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I have a highly sparse matrice and I need to invert them, but I need only somes values.

Complete inversion of a matrix take very long time to perform, but partial inversion is very very fast (in theory, same time than factorization of matrix).

I used this publication ( https://hpcrd.lbl.gov/~linlin/publications/diagex.pdf) to writea small program to be able to invert only some value of my sparse matrix, but to do that, I need to have access to LU factorization.

Thanks you

Marc

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here is some comment from the expert, wouldthat be helpful to solve the problem:

PARDISO now supports sparse RHS and solution vectors (iparm(31)). Using this switch it might be possible to get a block of an inverse matrix faster than a complete inverse matrix. The idea is the same as mentioned below we solve a system AX=B. If B is an identity matrix, then X=inverse(A). If the customer wants to have partial inverse, she should use sub-matrix of an identity matrix and indicate that only partial solution is needed through iparm(31) and proper perm settings as described in MKL Manual.

Thanks,

Chao

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So, using permutation vector will not be faster.

The better and fastest way to calculate partial inversion is algorithm described earlier. But to do that, we need to have access to L and U.

I know that UMFpack solver gives access to L et U after factorization.

I think one interesting solution would be to give access to the L and U after the factorization like in UMFPack.

Another solution would be to implement the algorithm described earlier in Intel PARDISO.

Thanks

Marc

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