ichol encountered a nonpositive pivot
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I have 2527676x2527676 sparse matrix K that ichol gives up easily with the ''ichol encountered a nonpositive pivot'' error. I tried re-odering, decreasing drop tol, level of fil and type of fil. I checked that diag(diag(K)==0) shows three zeros on the main diagonal. Regularization with speye function eliminates them but the solution with pcg is not correct. Any recommendations?
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aniket singh
on 29 Nov 2020
from the documentation: https://in.mathworks.com/help/matlab/ref/ichol.html
they suggest using the diagcomp option.
"
If ichol breaks down as above, you can use the diagcomp option to construct a shifted incomplete Cholesky factorization. That is, instead of constructing L such that L*L' approximates A, ichol with diagonal compensation constructs L such that L*L' approximates M = A + alpha*diag(diag(A)) without explicitly forming M. As incomplete factorizations always exist for diagonally dominant matrices, alpha can be found to make M diagonally dominant
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