[Trilinos-Users] [EXTERNAL] Amesos Superlu/Superludist Question

[Siva Rajamanickam]

Hi Travis,
 The useTranspose is used in lot of Amesos solvers as a shortcut to go 
between row storage and column storage (without copying), when the TPL 
requires a column storage and it can support a transpose solve. This 
appears to be a bug while computing the residuals though (as we don't 
use the trick for Superlu_dist). Do you get the correct answer when 
useTranspose() is false ?

Siva

Travis Austin wrote:
> Hi,
>
> I am using Amesos Superlu and Superludist to solve a very simple nonsymmetric problem.  There is agreement in the
> solution between the two problems but the residual ||Ax - b|| is not in agreement.  (See below.)
>
> Amesos_Superlu:
> ===================
> Amesos_Superlu : vector 0, ||Ax - b|| = 0
> Amesos_Superlu : vector 0, ||x|| = 0.25, ||b|| = 1
>
> Amesos_Superludist:
> ===================
> Amesos_Superludist : vector 0, ||Ax - b|| = 0.5
> Amesos_Superludist : vector 0, ||x|| = 0.25, ||b|| = 1
>
> The residual is being printed out because I am setting the ComputeTrueResidual parameter to true.  
>
> In Amesos_Superludist.cpp I see the method Amesos_Superludist::Solve() actually compute the residual and issues the
> following call:
>
>   if (ComputeTrueResidual_)
>     ComputeTrueResidual(*RowMatrixA_, *vecX, *vecB, UseTranspose(),
>                         "Amesos_Superludist");
>
> Furthermore, for Superludist UseTranspose() always returns true implying that I am computing ||A^t x - b||.  This is exactly
> what I have found for my small example matrix and explains the nonzero residual above in Amesos_Superludist.
>
> Can someone explain why UseTranspose() is hard coded to return true in Amesos_Superludist.h:118-120
>
> 118   //! Always returns true.
> 119   bool UseTranspose() const {return(true);};
> 120   //@}
>
> I'd think it should return false since it says that Superludist does not support transpose solves.
>
> Thanks,
> Travis
>
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Travis Austin, Ph.D.
> VP of Computational Mathematics
> Tech-X Corporation
> 5621 Arapahoe Ave, Suite A
> Boulder, CO 80303
> austin at txcorp.com
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>
>
>
>
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