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This topic contains 3 replies, has 2 voices, and was last updated by Dimitar 1 year, 11 months ago.
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.
(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.
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?
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.
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PARALUTION 1.1.0 - 25th of Jan 2016