<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On Jun 4, 2025, at 1:06 PM, Mark Adams <mfadams@lbl.gov> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr">It looks like it pivots in blocks and is a point-wise ILU: <a href="https://urldefense.us/v3/__https://petsc.org/release/manualpages/PC/PCILU/__;!!G_uCfscf7eWS!d82xhlyQ6-cWmSO0PBI3pnGPDROVlCOPZn87hYtI4Pi9Kkbf4wgpQjnYsrJVy0pwHGtZYvPKXDxQCoq9BTvE6Ao$">https://petsc.org/release/manualpages/PC/PCILU/</a><div><br></div><div>Mark</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Wed, Jun 4, 2025 at 9:36 AM Frank Bramkamp <<a href="mailto:bramkamp@nsc.liu.se">bramkamp@nsc.liu.se</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear PETSc team,<br>
<br>
I have a general question regarding the implementation of the inverse<br>
For the ILU factorization.<br>
<br>
I am looking e.g. on the implementation for block size 6 for the BAIJ matrix format in serial:<br>
src/mat/impls/baij/seq/dgefa6.c<br>
<br>
I wonder:<br>
You are using pivoting in the inverse computation.<br>
<br>
But if one changes the position of elements or rows, do we not have to apply an inverse permutation at the end<br>
to get the inverse of the original matrix to some column ?! Otherwise it is the inverse of the permutated matrix ?!<br></blockquote></div></div></blockquote><div><br></div> To compute the explicit inverse it does 6 triangular solves with columns of the identity. During the triangular solves it does the needed permutations so the inverse is the inverse of the original matrix, not a permuted version.<br><blockquote type="cite"><div><div class="gmail_quote gmail_quote_container"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
I am not quite sure if one has to do this in principle or if my understanding is not quite correct.<br>
Maybe I miss something in your code.<br>
<br>
<br>
Thanks, Frank<br>
<br>
<br>
<br>
</blockquote></div>
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