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<p class="MsoNormal"><span lang="FR">Dear PETSc community,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR"><o:p> </o:p></span></p>
<p class="MsoNormal">I am currently struggling with the ADD_VALUE mode of the Scatter object. Here is a simple piece of (Python) code to illustrate the issue:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_1</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#4EC9B0;mso-fareast-language:EN-GB">PETSc</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.Vec().createMPI(</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">size</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">10</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_1</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.shift(</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">2.0</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_2</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#4EC9B0;mso-fareast-language:EN-GB">PETSc</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.Vec().createMPI(</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">size</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">10</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_2</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.shift(</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">1.0</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">index_set</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#4EC9B0;mso-fareast-language:EN-GB">PETSc</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.IS().createStride(</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">10</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">step</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#B5CEA8;mso-fareast-language:EN-GB">1</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">scatter</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#4EC9B0;mso-fareast-language:EN-GB">PETSc</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.Scatter().create(</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_1</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">index_set</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_2</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">index_set</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:12.0pt;background:#1F1F1F"><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">scatter</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">.scatter(</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_1</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">vec_2</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">,
</span><span style="font-size:9.0pt;font-family:Consolas;color:#9CDCFE;mso-fareast-language:EN-GB">addv</span><span style="font-size:9.0pt;font-family:Consolas;color:#D4D4D4;mso-fareast-language:EN-GB">=</span><span style="font-size:9.0pt;font-family:Consolas;color:#569CD6;mso-fareast-language:EN-GB">True</span><span style="font-size:9.0pt;font-family:Consolas;color:#CCCCCC;mso-fareast-language:EN-GB">)<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Vectors vec_1 and vec_2 are respectively filled-in with 2.0 and 1.0. After the scattering, I would expect to have in vec_2 the sum of the values initially in vec_2 (that is 1.0) plus the values coming from vec_1 (that is 2.0).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But instead of having vec_2 filled in with 3.0 it is filled-in with 9.0. My understanding is that the number of processes (here 4 processes) plays a role since 9.0 = 1.0 (initial value) + 2.0 (values coming from vec_1) x 4 (number of processes).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is there a way to have simply 3.0 as a result?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hoping to have been clear enough, best regards,<o:p></o:p></p>
<p class="MsoNormal">Alexandre.<o:p></o:p></p>
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