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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">I have a piece of code which generates a matrix in CSR format, but the without sorting the column indexes in increasing order within each row. This seems not to be 100% compatible
with the MATMPIAIJ format: the documentation of MatCreateMPIAIJWithArrays indeed mentions 'row-major ordering'.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">For example, consider the 2x2 matrix (1 2; 3 4), which in my code could be stored as i=[0, 2, 4], j=[1, 0, 0, 1], v=[2, 1, 3, 4]. I can generate the matrix as follows (on 1 proc):
MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, 2, 2, 2, 2, i, j, v, &matrix). This appears to work fine, and I can then use the matrix in a KSP for example. However, if I try to update the entry values (same order and values v=[2, 1, 3, 4]) with MatUpdateMPIAIJWithArray(matrix,
v), it seems that PETSc does not memorize the order of the column indexes and the matrix that I get now is (2 1; 3 4). I get the same result with MatUpdateMPIAIJWithArrays(matrix, 2, 2, 2, 2, i, j, v). On the other hand, if the column indexes are sorted within
each row (i=[0, 2, 4], j=[0, 1, 0, 1], v=[1, 2, 3, 4]), then it works fine. I have attached a minimal working example (C++).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Can I safely rely on MatCreateMPIAIJWithArrays working fine with unsorted column indexes as long as I do not use MatUpdateMPIAIJWithArray(s)? Or should I do the sorting myself
before calling MatCreateMPIAIJWithArrays? (or alternatively use another matrix format).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Thanks in advance for the help.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Kind regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Mathieu Deuse<o:p></o:p></span></p>
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