<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, Sans-Serif;font-size:13px"><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span>Hello,</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span id="yui_3_16_0_ym19_1_1487214835214_14726">Newbie question again - data storage and distribution related this time </span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span><br></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_12387">I have briefly looked at the user manual, and searched forum, trying to get some basic understanding of the data storage and distribution. Some questions I have:</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span><br></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_12392">1. Sequential vs. Parallel</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_12412"> I assume that by 'sequential', we mean the matrix/vector is created in one process only ?</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_12536"> Then if this correct, I can assume that 'parallel' means each process will create a sub-matrix/vector for itself ?</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span><br></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_12534"> Will each process eventually have the complete matrix and the RHS vector after MatAssemblyBegin() and MatAssemblyEnd(), before solve starts ?</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12532"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12532">2. How the matrix/vector is split among the processes ?</div><div id="yui_3_16_0_ym19_1_1487214835214_12532"> I think matrix will be split by blocks of rows ? Does PETSc equally divide the matrix rows (with the last taking the remainder ) ?</div><div id="yui_3_16_0_ym19_1_1487214835214_12546"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"> If I want to create the matrix in a parallel way, do I have to divide the rows equally, or different process can have different number of rows, and some may not have any rows ?</div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"> Does RHS vector also need to be split in the exactly same blocks of rows as the matrix A (same start and end row number for the same process) ?</div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><font size="2" id="yui_3_16_0_ym19_1_1487214835214_12888">3. <span style="font-family: "Times New Roman";" id="yui_3_16_0_ym19_1_1487214835214_12767">MAT_STRUCTURALLY_SYMMETRIC</span></font></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><span style="font-family: "Times New Roman";" id="yui_3_16_0_ym19_1_1487214835214_12789"><font size="2" id="yui_3_16_0_ym19_1_1487214835214_12887"> Do I have to input the upper triangle portion of non zero values, or lower triangle is also fine ?</font></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12546" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span><br></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244" dir="ltr"><span id="yui_3_16_0_ym19_1_1487214835214_18321">4. Given the matrix A and RHS b, data type and sparsity, is there a way to estimate the total RAM needed for the solve phase, let's say for GMRES algorithm ?</span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span><br></span></div><div id="yui_3_16_0_ym19_1_1487214835214_12244"><span>many thanks !</span></div><div></div><div id="yui_3_16_0_ym19_1_1487214835214_12245"> </div><div class="signature" id="yui_3_16_0_ym19_1_1487214835214_12246">rgds<br>LX</div></div></body></html>