[Trilinos-Users] time cost by AztecOO::Iterate(int MaxIters, double Tolerance)

[Siva Rajamanickam]

Are you using Aztec's native preconditioners ? If yes, then do you call 
ConstructPreconditioner() before calling Iterate. If you don't do that 
then Aztec computes the preconditioner in the first iteration and your 
/timeUsedByCallingIterate /might include that cost as well.

Siva

Henian Xia wrote:
> Hello everyone,
> In my application, I have to call AztecOO::Iterate(int MaxIters,double 
> Tolerance) to solve the equation Ax=b. There is output like below when 
> calling this function:
>
>         /*******************************************************
>         ***** Problem: Epetra::CrsMatrix
>         ***** Preconditioned GMRES solution
>         ***** 1 step block Jacobi
>         ***** No scaling
>         *******************************************************
>                 iter:    0           residual = 1.000000e+00
>                 ....
>                 iter:   41           residual = 3.345028e-08
>                 iter:   42           residual = 2.219359e-08
>                 iter:   43           residual = 1.459019e-08
>                 iter:   44           residual = 9.729064e-09
>         Solution time: 0.051379 (sec.)
>         total iterations: 44/
>
> But I found that the displayed "Solution time" was sometimes much 
> smaller than the real time. For example, I used the following simple 
> code to time the calling to that method.
>
> /double ttemp3 = MPI_Wtime();
> (*solver).Iterate(2000, 1.0E-8);
> double ttemp4 = MPI_Wtime();
> double timeUsedByCallingIterate = ttemp4 - ttemp3;/
>
> Especially when I use multiple CPUs, such as 960 cores, the difference 
> between the calculated "timeUsedByCallingIterate" and the output 
> "Solution time" can be huge. Why is this happening please?
>
> Thank you,
> Henian
> -- 
> Henian Xia
> Graduate Research Assistant
> Department of MABE
> University of Tennessee, Knoxville
> ------------------------------------------------------------------------
>
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