[Trilinos-Users] Adding sparse matrices

[Maxsim Gibiansky]

> As the function's comments state, it doesn't matter whether the result
> has already been 'Filled()' or not, on entry to the function.

I tried it, and it still gave me an error. Here's code that I can run in the
python interpreter:

from PyTrilinos import Epetra
from PyTrilinos import EpetraExt

Comm = Epetra.PyComm()
Map = Epetra.Map(3,0,Comm)
A=Epetra.FECrsMatrix(Epetra.Copy, Map,1)
B=Epetra.FECrsMatrix(Epetra.Copy, Map,1)
C=Epetra.FECrsMatrix(Epetra.Copy, Map,1)

B[0,0]=1
C[1,1]=2

B.FillComplete()
C.FillComplete()

EpetraExt.Add(B, False, 1, A, 1)
EpetraExt.Add(C, False, 1, A, 1)

This gives me the following error after the last line:

python2.3: ../../../../packages/epetraext/src/EpetraExt_MatrixMatrix.cpp:1359:
static int EpetraExt::MatrixMatrix::Add(const Epetra_CrsMatrix&, bool, double,
Epetra_CrsMtrix&, double): Assertion `err == 0' failed.
Aborted

I'm using trilinos 7.0.8.

In the description of the Add function, it also says about the FillComplete
condition - "If it has, then B's graph must already contain all nonzero
locations that will be produced when forming the sum." I think I can only use
this if I am sure that the two matrices can be added without generating any new
nonzero locations in B, which might not be the case. 

I guess in this test case, it's possible to get around the problem by just
accumulating them in the right order, so that two matrices that are both
Filled() never need to be added. However, that doesn't seem like it'll work in
the general case, since some of the matrices to be added together might already
start out FillComplete()d if they were generated by, say, a multiplication. 

-Maxsim Gibiansky

Quoting "Williams, Alan B" <william at sandia.gov>:

> Maxsim,
> 
> The function MatrixMatrix::Add(A, transA, scalA, B, scalB)
> Forms the result B = scalA * A + scalB * B
> 
> As the function's comments state, it doesn't matter whether the result
> has already been 'Filled()' or not, on entry to the function.
> 
> In your scenario, A is the result matrix which makes the above somewhat
> confusing, but the bottom line is, you shouldn't get an error if the
> result matrix is already 'Filled()' on entry to the second Add.
> 
> Alan
> 
> 
> > -----Original Message-----
> > From: trilinos-users-bounces at software.sandia.gov 
> > [mailto:trilinos-users-bounces at software.sandia.gov] On Behalf 
> > Of Maxsim Gibiansky
> > Sent: Monday, June 11, 2007 1:02 PM
> > To: trilinos-users at software.sandia.gov
> > Subject: [Trilinos-Users] Adding sparse matrices
> > 
> > I've been using Trilinos (via PyTrilinos), and I have some 
> > other questions. 
> > 
> > I'm in a situation where I have sparse matrices 
> > (Epetra.FECrsMatrix) for several terms in an equation; I'd 
> > like to be able to add them. I've tried using the Add 
> > function in EpetraExt::MatrixMatrix, but I've had problems - 
> > at the end of the operation, the destination matrix has 
> > FillComplete() called on it. So if I wanted to use it to do 
> > something like
> > 
> > Add(B, False, 1, A, 1) // A += B
> > Add(C, False, 1, A, 1) // A += C
> > 
> > I might get an error, because A will already be Filled() 
> > after the first call. 
> > 
> > Am I missing something? I can't seem to figure out how to add 
> > a group of matrices together, and it seems like there should 
> > be some way of doing this. 
> > 
> > -Maxsim Gibiansky
> > 
> > 
> > _______________________________________________
> > Trilinos-Users mailing list
> > Trilinos-Users at software.sandia.gov
> > http://software.sandia.gov/mailman/listinfo/trilinos-users
> > 
> 
>