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<div dir="ltr">Maahi :<br>
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<div dir="ltr">Hello All,
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<div>I have some questions regarding ex2.c in /<i>petsc/src/ksp/ksp/examples/tutorials/ex2.c. </i></div>
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<div>1. The local sizes of the matrix was decided by PETSc using <i>ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);CHKERRQ(ierr);</i></div>
<div>But without knowing the local sizes, how was the following function used which requires the knowledge of how the big matrix was split into smaller chunks within PETSc? </div>
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<div> <i>ierr = MatMPIAIJSetPreallocation(A,5,NULL,5,NULL);CHKERRQ(ierr);</i></div>
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<div>This example sets a matrix for 2D 5-point PDE stencil, for which the maximum non-zeros in each row is 5. </div>
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<div>2. When using <i>MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr), </i>the global index of first and last row of which local chunk of the big matrix is it returning ? I mean if the big matrix was split into three processes, for example, fist and
last global row of which process is it returning? </div>
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<div>Adding a line </div>
<div> ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr);</div>
<div>+ printf("Istart %d Iend %d\n",Istart,Iend); </div>
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<div>I get</div>
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<div>$ mpiexec -n 3 ./ex2</div>
<div>Istart 0 Iend 19</div>
<div>Istart 19 Iend 38</div>
<div>Istart 38 Iend 56</div>
<div>Norm of error 0.000522061 iterations 9</div>
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<div>The matrix global size = 56</div>
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<div>Hong</div>
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<div>Your replies are highly appreciated</div>
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<div>Thanks,</div>
<div>Maahi Talukder</div>
<div>Clarkson University </div>
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