[Trilinos-Users] Symmetric Epetra_CrsMatrix ?

[Antoine Dechaume]

Hi Mike,

thanks for your answer. Is there a way I could use this trick with an  
iterative solver ?

Antoine.


On 28-Nov-08, at 3:55 PM, Heroux, Michael A wrote:

> Antoine,
>
> There is no explicit support for symmetric storage.  However, it is  
> possible to realize the storage savings by storing the main diagonal  
> as an Epetra_Vector object and the strictly upper or lower triangle  
> as an Epetra_CrsMatrix object.  Then computing y = Ax would be  
> approximatly as follows:
>
> // upperA and diagA were previously constructed
>
> Epetra_Vector Atx(y.Map());
>
> upperA.Multiply(false, x, y);
> upperA.Multiply(true, x, Atx);
> diagA.Multiply(1.0, diagA, x, y, 1.0);
> y.Update(1.0, Atx, 1.0);
>
> Note that if your x and y are Epetra_MultiVectors, the same sequence  
> works if you make Atx a MultiVector.
>
> There are other combinations of functions that will work also.  This  
> approach does not get the computational performance that a true  
> symmetric matvec would get, but does save storage.   We have  
> discussed a symmetric multiply function in the past, but have not  
> followed through on its implementation.  When considered in the  
> larger context of preconditioned iterative methods, full support for  
> symmetric storage is a large effort and its payoff is hard to  
> realize for our typical problem base that is primarily a broad set  
> that is mostly nonsymmetric.
>
> We will continue to evaluate the value of native support for  
> symmetric storage.
>
> I hope this helps.
>
> Mike
>
>
> On 11/27/08 2:43 PM, "Antoine Dechaume" <boolegue at gmail.com> wrote:
>
> Hello,
>
> is there a way to specify a symmetric Epetra_CrsMatrix that will store
> only upper part for instance ?
>
> Antoine.
>
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