[Trilinos-Users] AztecOO convergence

[Heroux, Michael A]

Bui,

Just to be clear. The 1e-12 residual value comes from computing the same residual expression?  In other words, with AztecOO you are scaling the residual by the norm of the RHS.  Does the 1e-12 also reflect scaling by the RHS?

I just want to make sure you are doing an "apples-to-apples" comparison of residuals.

If the residual expressions are the same, the issue could be a lack of convergence.  Are you restarting the GMRES iterations?  If so, try increasing the restart value.  For instance, set it to 1000 and see if convergence improves.  You may find that you will converge much quicker and then be able to set the restart size to a smaller value.  The value you want to set is AZ_kspace:


  solver.SetAztecOption(AZ_kspace, maxIters);

Where  maxIters is the maximum number of iterations you want to perform.

In general, for tough problems, I try to avoid any restart at all.

Let me know what you find out.

Mike

From: Hoang Giang Bui <hgbk2008 at gmail.com<mailto:hgbk2008 at gmail.com>>
Date: Friday, June 28, 2013 7:57 AM
To: "Ramsey, James J CIV (US)" <james.j.ramsey14.civ at mail.mil<mailto:james.j.ramsey14.civ at mail.mil>>, "trilinos-users at software.sandia.gov<mailto:trilinos-users at software.sandia.gov>" <trilinos-users at software.sandia.gov<mailto:trilinos-users at software.sandia.gov>>
Subject: [EXTERNAL] Re: [Trilinos-Users] AztecOO convergence


That's correct. I used it to benchmark the iterative one.

Bui



On Fri, Jun 28, 2013 at 1:58 PM, Ramsey, James J CIV (US) <james.j.ramsey14.civ at mail.mil<mailto:james.j.ramsey14.civ at mail.mil>> wrote:
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The matrix is scaled in my problem. Before solving this, I do a LeftScaling and observe that it gives better convergence. However, considering that MKL solver can solve my problem with tolerance 1e-12. I'm confused that iterative solver cannot give the result with the required tolerance.

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Is the MKL solver a direct solver?









--
With Best Regards !
Giang Bui
To learn and to excel
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