[Trilinos-Users] Teuchos::SerialDenseSolver equilibration: unexpected behavior

[Nico Schlömer]

Problem solved.

There is a bug in the Teuchos::Serial*DenseSolver: The unequilibration 
was actually carried out on the *RHS* whereas it should be the LHS. This 
basically means that the equilibration never worked if there was a 
column scaling.

Patch attached.

I also noticed that in the respective solve() methods, the equilibration 
is never automatically done:

============= *snip* =============
   if (ierr1!=0)
     return(ierr1);
   else
     return(ierr);

   // one never gets here
   if (equilibrate_) ierr1 = unequilibrateLHS();
   return(ierr1);
}
============= *snap* =============

-- I guess the maintainer may want to have a look at this.

Cheers,
Nico



On 10/19/2011 03:45 PM, Nico Schlömer wrote:
> Hi,
>
> I just encountered a rather odd behavior of Teuchos::SerialDenseSolver
> when used with equilibration.
> After building a specific 3x3 equation system (code attached), I call
>
> solver.solve();
>
> without equilibration and get the output
>
> ================ *snip* ================
> WARNING! SerialDenseSolver<T>::solve: System should be equilibrated!
> -0.0416252 0.836261 0.358417
> ================ *snap* ================
>
> This solution is correct. Using
>
> solver.equilibrateMatrix();
> solver.equilibrateRHS();
> solver.solve();
> solver.unequilibrateLHS();
>
> however, produces
>
> ================ *snip* ================
> -0.0416252 0.653305 0.323626
> ================ *snap* ================
>
> I guess I must be making some sort of mistake here but I fail to see
> what the issue could be.
> The comments in ./packages/amesos2/src/Amesos2_Lapack_def.hpp suggest
> that there may be more to it.
> Any hints?
>
> Cheers,
> Nico
>
>
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