[Trilinos-Users] AztecOO and Problem Size
Ammar T. Al-Sayegh
alsayegh at purdue.edu
Sat Nov 19 16:27:28 MST 2005
Hi All,
I'm using AztecOO to solve a reduced linear problem
(reuction done with EpetraExt_SubCopy_CrsMatrix fix).
Since the reduced matrix is symmetric positive definite,
I am using AZ_gc for higher efficiency. However, I keep
getting the following warning message:
AZ_check_options: WARNING: Preconditioned matrix may
not be symmetric (due to overlap).
Even with clearly symmteric matrices like this one:
Number of Global Rows = 3
Number of Global Cols = 3
Number of Global Diagonals = 3
Number of Global Nonzeros = 9
Global Maximum Num Entries = 3
Number of My Rows = 3
Number of My Cols = 3
Number of My Diagonals = 3
Number of My Nonzeros = 9
My Maximum Num Entries = 3
P Row Col Value
0 3 3 0.805556
0 3 4 0
0 3 5 0
0 4 3 0
0 4 4 6.21571e-10
0 4 5 -1.11883e-05
0 5 3 0
0 5 4 -1.11883e-05
0 5 5 0.268519
Why does AztecOO think that this matrix could not be
symmetric? and how can I prevent it from thinking this
way?
The other issue I have is with problem size. Once my
problem exceeds certain size I get the following error:
Epetra ERROR -3, AztecOO.cpp, line 824
on a single processor, which indicates that a numerical
loss of accuracy has occured. With more than a single
processor, I lose convergence even smaller problem sizes,
without even getting this error message.
Why am I losing convergence with bigger problem sizes?
and how come the same problem size that will solve with
single processor will not solve on more processors?
Thanks.
-ammar
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