<html>
<head>
<style><!--
.hmmessage P
{
margin:0px;
padding:0px
}
body.hmmessage
{
font-size: 10pt;
font-family:Tahoma
}
--></style>
</head>
<body class='hmmessage'><div dir='ltr'>
<br><div><br>
<meta http-equiv="Content-Type" content="text/html; charset=unicode">
<meta name="Generator" content="Microsoft SafeHTML">
<style>
.ExternalClass .ecxhmmessage P
{padding:0px;}
.ExternalClass body.ecxhmmessage
{font-size:10pt;font-family:Tahoma</style>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 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. <br><br>I am very hopeful that there is a way around to this problem, because PETSc is such a powerful and useful library that I really do not want to give up on this and start something else from scratch. <br><br><br>Would you think that a DIRECT SOLVER would circumvent this problem? My problem is that I have a very large system of equations and the size of a sparse coefficient matrix is huge ( > 1e+8). I assemble this matrix in MATLAB, write to a binary file, and read it in PETSc. So I really need to be able to solve this system of equations in a cluster of computers (which inherently has multiprocessors and distributed memory setting). Does this mean I am completely out of luck with PETSc's iterative solver package and the only hope for me is the direct solver? I do have MUMPS downloaded and compiled with PETSc, so I will give that a try and see what results I obtain, but I am really surprised that iterative solvers are no good in a large multiprocessor settings.<br><br>Any insights, suggestions/advice will be highly appreciated.<br><br>Thanks.<br><br>PS (I can attach my entire code, plots that compare the results obtained by solving Cx=b in 2 processors vs 12 or 6 processors if any body wants to take a look at it. I get garbage if I run iterative solver on 12 processors)<br> </div></div> </div></body>
</html>