<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;"><div><br></div> We need all the error output for the errors you got below to understand why the errors are happening.<br><div><br><blockquote type="cite"><div>On Feb 3, 2023, at 11:41 AM, Karthikeyan Chockalingam - STFC UKRI <karthikeyan.chockalingam@stfc.ac.uk> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 18px; 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;"><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Hello Barry,<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I would like to better understand<span class="Apple-converted-space"> </span></span><span style="font-size: 11pt;">pc_type redistribute usage.<span class="Apple-converted-space"> </span><o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I am plan to use pc_type<span class="Apple-converted-space"> </span><u>redistribute</u><span class="Apple-converted-space"> </span>in the context of adaptive mesh refinement on a structured grid in 2D. My base mesh (level 0) is indexed from 0 to N-1 elements and refined mesh (level 1) is indexed from 0 to 4(N-1) elements. When I construct system matrix A on (level 1); I probably only use 20% of 4(N-1) elements, however the indexes are scattered in the range of 0 to 4(N-1). That leaves 80% of the rows and columns of the system matrix A on (level 1) to be zero. From your earlier response, I believe this would be a use case for petsc_type redistribute.</span></div></div></div></blockquote><div><br></div> Indeed the linear solve will be more efficient if you use the redistribute solver. </div><div><br></div><div> But I don't understand your plan. With adaptive refinement I would just create the two matrices, one for the initial grid on which you solve the system, this will be a smaller matrix and then create a new larger matrix for the refined grid (and discard the previous matrix).<br><blockquote type="cite"><div><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 18px; 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;"><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Question (1)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">If N is really large, I would have to allocate memory of size 4(N-1) for the system matrix A on (level 1). How does pc_type redistribute<u><span class="Apple-converted-space"> </span></u>help? Because, I did end up allocating memory for a large system, where most of the rows and columns are zeros. Is most of the allotted memory not wasted?<u><span class="Apple-converted-space"> </span>Is this the correct usage?</u></span></div></div></div></blockquote><div><br></div> See above<br><blockquote type="cite"><div><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 18px; 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;"><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><u><o:p></o:p></u></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Question (2)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I tried using pc_type redistribute for a two level system.<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I have<span class="Apple-converted-space"> </span><b><u>attached</u></b><span class="Apple-converted-space"> </span>the output only for (level 1)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">The solution converges to right solution but still petsc outputs some error messages.<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">[0]PETSC ERROR: WARNING! There are option(s) set that were not used! Could be the program crashed before they were used or a spelling mistake, etc!<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">[0]PETSC ERROR: Option left: name:-options_left (no value)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">But the there were no unused options<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">#PETSc Option Table entries:<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-ksp_type preonly<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-options_left<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-pc_type redistribute<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-redistribute_ksp_converged_reason<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-redistribute_ksp_monitor_true_residual<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-redistribute_ksp_type cg<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-redistribute_ksp_view<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-redistribute_pc_type jacobi<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">#End of PETSc Option Table entries<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><b><span style="font-size: 11pt;">There are no unused options.<o:p></o:p></span></b></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Program ended with exit code: 0<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><br></span></div></div></div></blockquote>I cannot explain this<br><blockquote type="cite"><div><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 18px; 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;"><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><br>Question (2)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; background-color: white; font-size: 8.5pt; font-family: Menlo;"><span style="font-size: 11pt; font-family: Calibri, sans-serif;">[0;39m[0;49m[0]PETSC ERROR: Object is in wrong state<o:p></o:p></span></div><div style="margin: 0cm; background-color: white; font-size: 8.5pt; font-family: Menlo;"><span style="font-size: 11pt; font-family: Calibri, sans-serif;">[0]PETSC ERROR: Matrix is missing diagonal entry in row 0 (65792)<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">What does this error message imply? Given I only use 20% of 4(N-1) indexes, I can imagine most of the diagonal entrees are zero.<span class="Apple-converted-space"> </span><u>Is my understanding correct?</u><o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Question (3)<br><br><o:p></o:p></span></div><div style="margin: 0cm; background-color: white; font-size: 8.5pt; font-family: Menlo;">[0]PETSC ERROR: #5 MatZeroRowsColumnsIS() at /Users/karthikeyan.chockalingam/AMReX/SRC_PKG/petsc/src/mat/interface/matrix.c:6124</div><div style="margin: 0cm; background-color: white; font-size: 8.5pt; font-family: Menlo;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I am using MatZeroRowsColumnsIS to set the homogenous Dirichelet boundary. I don’t follow why I get this error message as the linear system converges to the right solution.<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Thank you for your help.<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Kind regards,<o:p></o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Karthik.<o:p></o:p></span></div><div style="margin: 0cm; background-color: white; font-size: 8.5pt; font-family: Menlo;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div style="border-style: solid none none; border-top-width: 1pt; border-top-color: rgb(181, 196, 223); padding: 3pt 0cm 0cm;"><p class="MsoNormal" style="margin: 0cm 0cm 12pt; font-size: 10pt; font-family: Calibri, sans-serif;"><b><span style="font-size: 12pt;">From:<span class="Apple-converted-space"> </span></span></b><span style="font-size: 12pt;">Barry Smith <<a href="mailto:bsmith@petsc.dev" style="color: blue; text-decoration: underline;">bsmith@petsc.dev</a>><br><b>Date:<span class="Apple-converted-space"> </span></b>Tuesday, 10 January 2023 at 18:50<br><b>To:<span class="Apple-converted-space"> </span></b>Chockalingam, Karthikeyan (STFC,DL,HC) <<a href="mailto:karthikeyan.chockalingam@stfc.ac.uk" style="color: blue; text-decoration: underline;">karthikeyan.chockalingam@stfc.ac.uk</a>><br><b>Cc:<span class="Apple-converted-space"> </span></b><a href="mailto:petsc-users@mcs.anl.gov" style="color: blue; text-decoration: underline;">petsc-users@mcs.anl.gov</a><span class="Apple-converted-space"> </span><<a href="mailto:petsc-users@mcs.anl.gov" style="color: blue; text-decoration: underline;">petsc-users@mcs.anl.gov</a>><br><b>Subject:<span class="Apple-converted-space"> </span></b>Re: [petsc-users] Eliminating rows and columns which are zeros<o:p></o:p></span></p></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> Yes, after the solve the x will contain correct values for ALL the locations including the (zeroed out rows). You use case is exactly what redistribute it for.<o:p></o:p></span></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> Barry<o:p></o:p></span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><br><br><o:p></o:p></span></div><blockquote style="margin-top: 5pt; margin-bottom: 5pt;"><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">On Jan 10, 2023, at 11:25 AM, Karthikeyan Chockalingam - STFC UKRI <<a href="mailto:karthikeyan.chockalingam@stfc.ac.uk" style="color: blue; text-decoration: underline;">karthikeyan.chockalingam@stfc.ac.uk</a>> wrote:<o:p></o:p></span></div></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Thank you Barry. This is great!</span></div></div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I plan to solve using ‘-pc_type redistribute’ after applying the Dirichlet bc using</span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span class="s1"><span style="font-size: 9pt; font-family: Menlo; color: rgb(108, 54, 169);">MatZeroRowsColumnsIS</span></span><span style="font-size: 9pt; font-family: Menlo;">(</span><span class="s2"><span style="font-size: 9pt; font-family: Menlo; color: rgb(50, 109, 116);">A</span></span><span style="font-size: 9pt; font-family: Menlo;">,<span class="apple-converted-space"> </span></span><span class="s2"><span style="font-size: 9pt; font-family: Menlo; color: rgb(50, 109, 116);">isout</span></span><span style="font-size: 9pt; font-family: Menlo;">,<span class="apple-converted-space"> </span></span><span class="s3"><span style="font-size: 9pt; font-family: Menlo; color: rgb(28, 0, 207);">1</span></span><span style="font-size: 9pt; font-family: Menlo;">,<span class="apple-converted-space"> </span></span><span class="s2"><span style="font-size: 9pt; font-family: Menlo; color: rgb(50, 109, 116);">x</span></span><span style="font-size: 9pt; font-family: Menlo;">,<span class="apple-converted-space"> </span></span><span class="s2"><span style="font-size: 9pt; font-family: Menlo; color: rgb(50, 109, 116);">b)</span></span><span style="font-size: 9pt; font-family: Menlo;">;<span class="apple-converted-space"> </span></span><span style="font-size: 9pt; font-family: Menlo;"><o:p></o:p></span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo;"> </span><span style="font-size: 9pt; font-family: Menlo;"><o:p></o:p></span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">While I retrieve the solution data from x (after the solve) – can I index them using the original ordering (if I may say that)?</span></div></div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Kind regards,</span></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Karthik.</span></div></div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div><div style="border-style: solid none none; border-top-width: 1pt; border-top-color: rgb(181, 196, 223); padding: 3pt 0cm 0cm;"><p class="MsoNormal" style="margin: 0cm 0cm 12pt; font-size: 10pt; font-family: Calibri, sans-serif;"><b><span style="font-size: 12pt;">From:<span class="apple-converted-space"> </span></span></b><span style="font-size: 12pt;">Barry Smith <</span><a href="mailto:bsmith@petsc.dev" style="color: blue; text-decoration: underline;"><span style="font-size: 12pt;">bsmith@petsc.dev</span></a><span style="font-size: 12pt;">><br><b>Date:<span class="apple-converted-space"> </span></b>Tuesday, 10 January 2023 at 16:04<br><b>To:<span class="apple-converted-space"> </span></b>Chockalingam, Karthikeyan (STFC,DL,HC) <</span><a href="mailto:karthikeyan.chockalingam@stfc.ac.uk" style="color: blue; text-decoration: underline;"><span style="font-size: 12pt;">karthikeyan.chockalingam@stfc.ac.uk</span></a><span style="font-size: 12pt;">><br><b>Cc:<span class="apple-converted-space"> </span></b></span><a href="mailto:petsc-users@mcs.anl.gov" style="color: blue; text-decoration: underline;"><span style="font-size: 12pt;">petsc-users@mcs.anl.gov</span></a><span class="apple-converted-space"><span style="font-size: 12pt;"> </span></span><span style="font-size: 12pt;"><</span><a href="mailto:petsc-users@mcs.anl.gov" style="color: blue; text-decoration: underline;"><span style="font-size: 12pt;">petsc-users@mcs.anl.gov</span></a><span style="font-size: 12pt;">><br><b>Subject:<span class="apple-converted-space"> </span></b>Re: [petsc-users] Eliminating rows and columns which are zeros</span><o:p></o:p></p></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><a href="https://petsc.org/release/docs/manualpages/PC/PCREDISTRIBUTE/#pcredistribute" style="color: blue; text-decoration: underline;"><span style="font-size: 11pt;">https://petsc.org/release/docs/manualpages/PC/PCREDISTRIBUTE/#pcredistribute</span></a><span style="font-size: 11pt;"> -pc_type redistribute</span></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">It does everything for you. Note that if the right hand side for any of the "zero" rows is nonzero then the system is inconsistent and the system does not have a solution.</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Barry</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><br><br><br></span></div></div><blockquote style="margin-top: 5pt; margin-bottom: 5pt;"><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">On Jan 10, 2023, at 10:30 AM, Karthikeyan Chockalingam - STFC UKRI via petsc-users <</span><a href="mailto:petsc-users@mcs.anl.gov" style="color: blue; text-decoration: underline;"><span style="font-size: 11pt;">petsc-users@mcs.anl.gov</span></a><span style="font-size: 11pt;">> wrote:</span></div></div></div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div><div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Hello,</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I am assembling a MATIJ of size N, where a very large number of rows (and corresponding columns), are zeros. I would like to potentially eliminate them before the solve.</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">For instance say N=7</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 0<span class="apple-converted-space"> </span>0<span class="apple-converted-space"> </span>0 0 0 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 1 -1<span class="apple-converted-space"> </span>0 0 0 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 -1 2<span class="apple-converted-space"> </span>0 0 0 -1</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 0<span class="apple-converted-space"> </span>0<span class="apple-converted-space"> </span>0 0 0 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 0<span class="apple-converted-space"> </span>0<span class="apple-converted-space"> </span>0 0 0 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 0<span class="apple-converted-space"> </span>0<span class="apple-converted-space"> </span>0 0 0 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif; background-color: white;"><span style="font-size: 9pt; font-family: Menlo; color: rgb(93, 108, 121);">0 0<span class="apple-converted-space"> </span>-1 0 0 0 1</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I would like to reduce it to a 3x3</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">1 -1 0</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">-1 2 -1</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">0 -1 1</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">I do know the size N.</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Q1) How do I do it?</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Q2) Is it better to eliminate them as it would save a lot of memory?</span></div></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Q3) At the moment, I don’t know which rows (and columns) have the zero entries but with some effort I probably can find them. Should I know which rows (and columns) I am eliminating?</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Thank you.</span></div></div></div><div><div><p class="MsoNormal" style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"> </span></p></div></div><div><div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;">Karthik.</span><o:p></o:p></div></div></div><p style="caret-color: rgb(0, 0, 0); font-variant-caps: normal; text-align: start; -webkit-text-stroke-width: 0px; word-spacing: 0px;"><span style="font-size: 6pt; font-family: Helvetica;">This email and any attachments are intended solely for the use of the named recipients. If you are not the intended recipient you must not use, disclose, copy or distribute this email or any of its attachments and should notify the sender immediately and delete this email from your system. UK Research and Innovation (UKRI) has taken every reasonable precaution to minimise risk of this email or any attachments containing viruses or malware but the recipient should carry out its own virus and malware checks before opening the attachments. UKRI does not accept any liability for any losses or damages which the recipient may sustain due to presence of any viruses. </span><span style="font-size: 13.5pt; font-family: Helvetica;"><o:p></o:p></span></p></div></blockquote></div></div></div></blockquote></div><div style="margin: 0cm; font-size: 10pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;"><o:p> </o:p></span></div></div></div><span id="cid:FB8F1146-2000-44A8-B84C-34005F14DF49"><petsc_redistribute.txt></span></div></blockquote></div><br></body></html>