<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Dear <span id="DWT146" class="ZmSearchResult"><span id="DWT154" class="ZmSearchResult">PETSc</span></span> team,<br><div><br></div><div><div>I'm currently working on the parallelization of the assembling of a system, previously assembled in a serial way (manual), but solved using <span id="DWT148" class="ZmSearchResult"><span id="DWT156" class="ZmSearchResult">PETSc</span></span> in parallel.<br></div><div>The problem I have is that when comparing computational time with the previous implementation, it seem that the parallel version is slower than the serial one.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>The type of matrices we deal with are sparse and might change their size in a significant order (kind of contact problems, where relations between elements change).<br data-mce-bogus="1"></div></div></div><div><div>For the example I'm using, for giving an example, the initial size of the matrix is : 139905, after several iteratinos it changes to: 141501 and finally to: 254172.</div><div><br></div></div><div>The system is assembled and solved at each iteration and the matrix can not be re-used, therefore for each new iteration the matrix is set to zero keeping the previous non-zero pattern, and the option 'MAT_NEW_NONZERO_LOCATIONS' is set to 'TRUE'.<br></div><div>In order to do the assembling I use the function 'MatSetValues' , inserting 3 lines and 3 rows, which might not be next to each other, and thus might no constitute a block. </div><div><br data-mce-bogus="1"></div><div>I believe that, what makes an important difference in time is the fact of adding almost the double of elements (from 139905 to 254172), but i don't know how what could I implement to retain a larger preallocation or to solve in any other way.<br></div><div>I don't know, neither, in advance the position of new elements so that I can think in placing zeros to, maybe, generate a pre-pattern.<br></div><div><br data-mce-bogus="1"></div><div>Do you have any idea of how could I improve the time of the parallel version?<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Thanks in advance!<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Regards, <br data-mce-bogus="1"></div><div>Catherine<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div></div></body></html>