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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> Strongly recommend using MatSetValues[Blocked][Local]() instead of MatCreateMPIAIJWithSplitArrays(). Just preallocate and set the values from wherever you know
them. This way, the same code will work immediately with different matrix formats and it's easier to transition to generating the matrix on-the-fly (rather than reading from disk which is always a bottleneck).<span style="color:#1F497D"><o:p></o:p></span></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Maybe I have not explained my situation well enough: I do already have a matrix on the disk. This makes generating the matrix on-the-fly either
a burden for the filesystem (because of to many accesses in a short time) or for the memory (because data has to be duplicated). I want to avoid both, thus read in my matrix in one go and pass this data conveniently to PETSc. As far as my insights go, there
are two possibilities with certain drawbacks, maybe you could uncover more details on both (like convenience of data layout, assembly time, solution speed, …).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">1.)MatCreateBAIJ (includes MatSetBlockSize and MatMPIBAIJSetPreallocation) > MatSetLocalToGlobalMapping > MatSetValuesBlockedLocal<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">drawbacks:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- data is copied (thus doubles memory needs)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- ALL local rows has to be read in to get information for preallocation<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- but: SetValuesBlockedLocal requires "square" layout of data (not suited for sparse matrices). In my case this leads to setting values (block)
row by (block) row.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- and: value array does not match block structure (cf. documentation example of MatSetValuesBlocked): my values are sorted sequentially by blocks,
i.e. v[] = [1,2,5,6,3,4,7,8,...]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">2.)MatCreateMPIAIJWithSplitArrays<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">drawbacks:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">? doesn't match PETSc data layout -> slower?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- not blocked (conversion to MPIBAIJ possible?)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Gregor Matura<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="punctuation-wrap:simple;text-autospace:none"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:dimgray">——————————————————————————<o:p></o:p></span></p>
<p class="MsoNormal" style="punctuation-wrap:simple;text-autospace:none"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:dimgray">Deutsches Zentrum für Luft- und Raumfahrt</span></b><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:dimgray">
e.V. (DLR)<o:p></o:p></span></p>
<p class="MsoNormal" style="punctuation-wrap:simple;text-autospace:none"><a name="Institut"></a><span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";color:dimgray">German Aerospace Center</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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