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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">I have a matrix system Ax = b, A is of type MatSeqAIJ or MatMPIAIJ, depending on the number of cores.
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<div>I try to solve this problem by pc_type ilu and ksp_type bcgs, it does not converge. The options I specify are:</div>
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-pc_type hypre -pc_hypre_type pilut -pc_hypre_pilut_maxiter 1000 -pc_hypre_pilut_tol 1e-3 -ksp_type b\</p>
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cgs -ksp_rtol 1e-10 -ksp_max_it 1000 -ksp_monitor_short -ksp_converged_reason</p>
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<p style="margin-right: 0px; margin-left: 0px;"><font size="2">The first a few lines of the output are:</font></p>
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0 KSP Residual norm 1404.62 </p>
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1 KSP Residual norm 88.9068 </p>
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2 KSP Residual norm 64.73 </p>
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3 KSP Residual norm 71.0224 </p>
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4 KSP Residual norm 69.5044 </p>
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5 KSP Residual norm 455.458 </p>
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6 KSP Residual norm 174.876 </p>
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7 KSP Residual norm 183.031 </p>
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8 KSP Residual norm 650.675 </p>
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9 KSP Residual norm 79.2441 </p>
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10 KSP Residual norm 84.1985</p>
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<p style="margin-right: 0px; margin-left: 0px;"><font size="2">This clearly indicates non-convergence. However, I output the sparse matrix A and vector b to MATLAB, and run the following command:</font></p>
<p style="margin-right: 0px; margin-left: 0px;">[L,U] = ilu(A,struct('type','ilutp','droptol',1e-3));</p>
<p style="margin-right: 0px; margin-left: 0px;">[ux1,fl1,rr1,it1,rv1] = bicgstab(A,b,1e-10,1000,L,U);</p>
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<p style="margin-right: 0px; margin-left: 0px;">And it converges in MATLAB, with flag fl1=0, relative residue rr1=8.2725e-11, and iteration it1=89.5. I'm wondering how can I figure out what's wrong. </p>
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<p style="margin-right: 0px; margin-left: 0px;">Best, </p>
<p style="margin-right: 0px; margin-left: 0px;">Hui</p>
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