<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;">To expand on Barry’s answer, we have observed repeatedly that MatMatMult with MatAIJ performs better than MatMult with MatMAIJ, you can reproduce this on your own with <a href="https://petsc.org/release/src/mat/tests/ex237.c.html">https://petsc.org/release/src/mat/tests/ex237.c.html</a>.<div>Also, I’m guessing you are using some sort of preconditioner within your KSP.</div><div>Not all are “KSPMatSolve-ready”, i.e., they may treat blocks of right-hand sides column by column, which is very inefficient.</div><div>You could run your code with -info dump and send us dump.0 to see what needs to be done on our end to make things more efficient, should you not be satisfied with the current performance of the code.</div><div><br></div><div>Thanks,</div><div>Pierre<br><div><br><div><blockquote type="cite"><div>On 7 Dec 2023, at 8:34 PM, Barry Smith <bsmith@petsc.dev> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><br class="Apple-interchange-newline"><br><blockquote type="cite"><div>On Dec 7, 2023, at 1:17 PM, Sreeram R Venkat <srvenkat@utexas.edu> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr"><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div style="color: rgb(34, 34, 34);">I have 2 sequential matrices M and R (both MATSEQAIJCUSPARSE of size n x n) and a vector v of size n*m. v = [v_1 , v_2 ,... , v_m] where v_i has size n. The data for v can be stored either in column-major or row-major order. Now, I want to do 2 types of operations:</div><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">1. Matvecs of the form M*v_i = w_i, for i = 1..m. </div><div style="color: rgb(34, 34, 34);">2. KSPSolves of the form R*x_i = v_i, for i = 1..m.</div><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">From what I have read on the documentation, I can think of 2 approaches. </div><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">1. Get the pointer to the data in v (column-major) and use it to create a dense matrix V. Then do a MatMatMult with M*V = W, and take the data pointer of W to create the vector w. For KSPSolves, use KSPMatSolve with R and V.</div><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">2. Create a MATMAIJ using M/R and use that for matvecs directly with the vector v. I don't know if KSPSolve with the MATMAIJ will know that it is a multiple RHS system and act accordingly.</div><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">Which would be the more efficient option?</div></div></div></div></div></blockquote><div><br></div>Use 1. <br><blockquote type="cite"><div><div dir="ltr"><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">As a side-note, I am also wondering if there is a way to use row-major storage of the vector v.</div></div></div></div></div></blockquote><div><br></div>No</div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><br><blockquote type="cite"><div><div dir="ltr"><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div style="color: rgb(34, 34, 34);">The reason is that this could allow for more coalesced memory access when doing matvecs.</div></div></div></div></div></blockquote><div><br></div> PETSc matrix-vector products use BLAS GMEV matrix-vector products for the computation so in theory they should already be well-optimized</div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><br><blockquote type="cite"><div><div dir="ltr"><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div style="color: rgb(34, 34, 34);"><br></div><div style="color: rgb(34, 34, 34);">Thanks,</div><div style="color: rgb(34, 34, 34);">Sreeram</div></div></div></div></div></blockquote></div></div></blockquote></div><br></div></div></body></html>