FGMRES faster than GMRES

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This topic contains 3 replies, has 2 voices, and was last updated by  Mohamed 8 months ago.

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  • #1489

    Mohamed
    Member

    Hi,
    I observed for the matrices and RHS I generate in my case that FGMRES is faster than GMRES, while both use ILU and show the same number of linear iterations to convergence.

    I expected FGMRES with the same preconditioner to have the same performance as GMRES since they performs the same linear iterations.

    Can you please comment on that (I could provide matrix and RHS )

    thanks
    Mohamed

    #1491

    Dimitar
    Member

    Hi Mohamed,

    Yes, this is a bit unexpected. Typically, FGMRES could require less iteration to convergence than the pure GMRES.

    Can you say something more about your linear system? How big is the problem?
    What kind of timing do you get?

    Best,
    Dimitar

    #1492

    Dimitar
    Member

    Correction, actually this FMGRES implementation uses one application of the preconditioner less. Thus, it should perform slightly better than the pure GMRES. You can check the files directly (gmres.cpp and fgmres.cpp)

    // Dimitar

    #1493

    Mohamed
    Member

    thanks Dimitar

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