<div class="gmail_quote">On Thu, Sep 8, 2011 at 19:57, amrit poudel <span dir="ltr"><<a href="mailto:amrit_pou@hotmail.com">amrit_pou@hotmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div dir="ltr">After running my simulation multiple times on a multiprocessor computer I've just verified that using iterative solver (default gmres) in PETSc to solve a linear system of equations ( Cx=b) with more than 2 processors setting ALWAYS lead to erroneous result. Running identical code with identical setting except for the number of processors ( set this to 2) ALWAYS gives me correct result .<br>
</div></blockquote><div><br></div><div>You have to explain what "erroneous result" means here.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div dir="ltr"><br>I am really not sure what is the point behind including iterative solvers if they result into erroneous result on a multiprocessor computer. The result I get from multiprocessor computer is a complete garbage, so I am really not talking about small percentage of error here. Also, if somebody could enlighten why the iterative solvers are error prone on multiprocessors that will be highly appreciated. </div>
</blockquote></div><br><div>Well let's not jump to conclusions. Iterative solvers can fail, as can direct solvers, but it's more common that (a) the problem you are building is not actually the same or the results are being misinterpreted or (b) the default methods are not working well and needs some algorithmic adjustments for your problem.</div>
<div><br></div><div>Please explain what kind of problem you are solving, how you are going about it, and what symptoms you have observed.</div>