<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
<br class="">
<div><br class="">
<blockquote type="cite" class="">
<div class="">On Jan 25, 2019, at 4:51 PM, Sajid Ali via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" class="">petsc-users@mcs.anl.gov</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div dir="ltr" class="">
<div dir="ltr" class="">
<div class="">Hi, <br class="">
<br class="">
</div>
If I have a linear time dependent equation I'm trying to solve using TS, I can use :<br class="">
TSSetProblemType(ts,TS_LINEAR);<br class="">
TSSetRHSFunction(ts,NULL,TSComputeRHSFunctionLinear,NULL);<br class="">
TSSetRHSJacobian(ts,A,A,YourComputeRHSJacobian, &appctx); <br class="">
<br class="">
</div>
<div class="">If the matrix that's being evaluated by YourComputeRHSJacobian is such that the non-zero structure stays the same and only the diagonal changes with time, is there a way to optimize the function so that it doesn't create the whole matrix from
scratch each time ? <br class="">
</div>
</div>
</div>
</blockquote>
<div><br class="">
</div>
<div>The matrix A should be created only once before TSSetRHSJacobian() is called. YourComputeRHSJacobian() does not need to create the whole matrix each time; it updates the values in A and assembles it.</div>
<br class="">
<blockquote type="cite" class="">
<div class="">
<div dir="ltr" class="">
<div class="">Naively I can make a dummy matrix and store the copy from t=0 and change the diagonal at each iteration but that unnecessarily doubles the memory consumption, is there a better way? </div>
</div>
</div>
</blockquote>
<div><br class="">
</div>
A is the working matrix storing the Jacobian. The matrix passed to YourComputeRHSJacobian() is actually A. There is no need to save an extra copy.</div>
<div><br class="">
</div>
<div>Hong (Mr.)</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="">
<div dir="ltr" class="">
<div dir="ltr" class="">
<div class="">
<div class=""><br class="">
</div>
<div class="">Thank You,<br class="">
</div>
<div class="">
<div dir="ltr" class="gmail_signature">
<div dir="ltr" class="">
<div style="font-size:12.8px" class="">Sajid Ali<br class="">
</div>
<div style="font-size:12.8px" class="">Applied Physics<br class="">
</div>
<div style="font-size:12.8px" class="">Northwestern University</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</blockquote>
</div>
<br class="">
</body>
</html>