<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hello Lucas,<div class="">In your sequence of systems, is A changing?</div><div class="">Are all right-hand sides available from the get-go?</div><div class="">In that case, you can solve everything in a block fashion and that’s how you could get real improvements.</div><div class="">Also, instead of PCCHOLESKY on A^T * A + KSPCG, you could use PCQR on A + KSPPREONLY, but this may not be needed, cf. Jed’s answer.</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Pierre</div><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 1 Mar 2022, at 12:54 AM, Lucas Banting <<a href="mailto:bantingl@myumanitoba.ca" class="">bantingl@myumanitoba.ca</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta charset="UTF-8" class=""><div style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;" class="">Hello,<br class=""><br class="">I have an MPIDENSE matrix of size about 200,000 x 200, using KSPLSQR on my machine a solution takes about 15 s. I typically run with six to eight processors.<br class="">I have to solve the system several times, typically 4-30, and was looking for recommendations on reusable preconditioners to use with KSPLSQR to increase speed.<br class=""><br class="">Would it make the most sense to use PCCHOLESKY on the smaller system A^T * A?<span class="Apple-converted-space"> </span><br class=""></div><div style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;" class=""><br class=""></div><div style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;" class="">Thanks,<br class="">Lucas</div></div></blockquote></div><br class=""></div></body></html>