<div dir="ltr"><div class="gmail_default" style="font-size:small">Hello,</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default">I am using KSPFGMRES as my linear solver for Ax=b system. I was wondering how the initial guess will influence the computation efficiency. Does PETSc always starts with xo=0 or some value else? If I use my previous solution as the initial guess for current computation  is it going to take less effort for PETSc to solve the system? (my configuration attached)</div><div class="gmail_default" style="font-size:small"><br>Thanks,<br>Paul</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default"><div class="gmail_default">        MatCreateMPIAIJ(</div><div class="gmail_default">                        PETSC_COMM_WORLD,</div><div class="gmail_default">                        grid[gid].cellCount*nVars,</div><div class="gmail_default">                        grid[gid].cellCount*nVars,</div><div class="gmail_default">                        grid[gid].globalCellCount*nVars,</div><div class="gmail_default">                        grid[gid].globalCellCount*nVars,</div><div class="gmail_default">                        0,&diagonal_nonzeros[0],</div><div class="gmail_default">                        0,&off_diagonal_nonzeros[0],</div><div class="gmail_default">                        &impOP);</div><div class="gmail_default"><br></div><div class="gmail_default">        KSPSetOperators(ksp,impOP,impOP,SAME_NONZERO_PATTERN);</div><div class="gmail_default">        KSPSetTolerances(ksp,rtol,abstol,1.e15,maxits);</div><div class="gmail_default">        KSPSetInitialGuessKnoll(ksp,PETSC_TRUE);</div><div class="gmail_default">        KSPSetType(ksp,KSPFGMRES);<br></div><div style="font-size:small"><br></div></div><div class="gmail_default" style="font-size:small"><br></div><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><div style="color:rgb(0,0,0)"><font size="1">Huaibao (Paul) Zhang<br><b><i>Gas Surface Interactions Lab</i></b><br></font></div><div style="color:rgb(0,0,0)"><font size="1">Department of Mechanical Engineering</font></div><div style="color:rgb(0,0,0)"><font size="1">University of Kentucky,</font></div><div style="color:rgb(0,0,0)"><font size="1">Lexington,</font></div><div style="margin:0px;font-family:Helvetica"><font size="1">KY, 40506-0503<b><br>Office</b>: 216 Ralph G. Anderson Building<br><b>Web</b>:<a href="http://gsil.engineering.uky.edu/" target="_blank"><span style="color:rgb(0,0,153)">gsil.engineering.uky.edu</span></a></font></div></div></div></div></div>
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