stopping criteria

Front page Forums General stopping criteria

This topic contains 3 replies, has 2 voices, and was last updated by  Dimitar 1 year, 5 months ago.

Viewing 4 posts - 1 through 4 (of 4 total)
  • Author
    Posts
  • #1423

    Mohamed
    Member

    I am analyzing the effect of the stopping criteria on GMRES
    for that I differentiate between:
    1) residual< epsilon
    2) residual< epsilon *||b||
    3) residual/r0< epsilon

    In Paralution condition 1 is absolute and 3 is relative. I don’t find the setting for the second condition.
    Is there a thought behind omitting condition 2?

    PS: in petsc they have 1 and 2 missing the third.

    #1424

    Dimitar
    Member

    Hi,

    (2) and (3) are the same for initial x = 0.

    For x != 0, you can specify (3) which is the relative stopping criteria as you mention.

    If you want to have (2) for x != 0, you need to modify a bit the IterationControl class.

    Best,
    Dimitar

    #1425

    Mohamed
    Member

    Hi Dimitar,
    thanks for your answer. I enforced 2) by taking 1) and multiplying by the norm of b.

    In a steady CFD simulation I keep calling the GMRES for every flow iteration and I hope x0(i+1) is set to the last x(i) or is it always x0=0?

    thanks
    Med

    #1426

    Dimitar
    Member

    Hi Med,

    In all iterative solvers you need to pass A, b, x. The x you pass is the initial guess (your x0). We do not modify the initial vector nor set it to zero.

    Best,
    Dimitar

Viewing 4 posts - 1 through 4 (of 4 total)

You must be logged in to reply to this topic.