<div><br></div><div><br><div class="gmail_quote"><div dir="ltr">On Tue, 9 Apr 2019 at 10:33, Mark Adams via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">PETSc solvers will cache any setup computations, like a matrix factorization, and will reuse them on subsequent solves. <div><br></div><div>If you call KSPSetOperators, PETSc will assume its cache is invalid and redo any required setup on subsequent solves.</div></div></blockquote><div dir="auto"><br></div><div dir="auto">Following from what Mark said, if you want an exact solve, use -pc_type lu. Note that this will not store the inverse, rather only the L, U factors. During setup, the L,U factors are created and subsequent solves will simply apply the forward and backward solves using these factors.</div><div dir="auto"><br></div><div dir="auto"><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div></div></div><div dir="ltr"><div><div><br></div><div>Mark</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Apr 9, 2019 at 4:08 AM ztdepyahoo via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</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">

    

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        <span>Dear group:
        </span></div><div><span>      I need to solve a Laplacian problem Ax=b every time step where A is a constant . I want to store the inverse of A at the first time step. </span></div><div><span>how to do with Petsc</span></div><div><span> Regards</span></div>
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