<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Dear Barry, <div class=""><br class=""></div><div class="">At the moment I’m dealing with the following problem.</div><div class=""><br class=""></div><div class="">Suppose I want to solve Sx=b, where is a product of matrices. In particular inside it contains also an inverse of a matrix.</div><div class="">To compute the action of S I have created a shell matrix, but know I would like to apply the ASM as preconditioner.</div><div class=""><br class=""></div><div class="">Citing your words as answer to a previous similar question:</div><div class=""><br class=""></div><div class=""><i style="font-family: -webkit-standard; background-color: rgb(255, 255, 255);" class="">Thu Jan 13 13:14:47 CST 2011</i></div><div class=""><i style="font-family: Times;" class="">Is it possible use ASM and/or FieldSplit with a matrix-free method?</i></div><div class=""><pre style="background-color: rgb(255, 255, 255);" class=""><pre class=""><font face="Times" class="">"Yes, BUT the algorithms are coded around MatGetSubMatrix() and or MatGetSubMatrices() so to do matrix free you need to have code that applies "part" of the operator at a time (that is you cannot just have a matrix vector product that applies the entire operator to the entire vector. Once you have the ability to apply "part" of the operator at a time you need to code up a MATSHELL that responds appropriately to MatGetSubMatrix() and or MatGetSubMatrices() and returns new matrix-free shell matrices that apply only "their" part of the operator. This is non-trivial for many people but possible."</font>
</pre><div class=""><br class=""></div><div class=""><font face="Helvetica" class="">Could you be so kind to explain me better how, or do you have some code that is doing something similar?</font></div><div class=""><font face="Helvetica" class=""><br class=""></font></div><div class=""><font face="Helvetica" class=""><br class=""></font></div><div class=""><font face="Helvetica" class="">Regards,</font></div><div class=""><font face="Helvetica" class=""><br class=""></font></div><div class=""><font face="Helvetica" class="">Sonia</font></div></pre></div></body></html>