On 12/6/20 12:27 PM, blais...@gmail.com wrote:
In this case, even using ILU(1) is extremely expensive (e.g. it takes 2X more
time than to assemble the matrix and it really doubles up the iteration time).
Consequently, we are using ILU(0), which in the present case is performing
relatively well (say between 40-100 iterations per newton step). I was
wondering if there were any other suggestions in terms of preconditioner that
we could use?
Our system : GLS stabilized Navier-Stokes, monolithic matrix formulation
(single matrix for u,v,w,p). The matrix is non-symmetric.
Our solver : Either GMRES or BiCGStab. In our case it seems GMRES is a bit
faster (around 20%) because the iterations are cheaper. I have tried all of
the solvers in the TrilinosWrappers except FGMRES actually.
Our current preconditioner : ILU(0)
Library used : Trilinos through the deal.II wrappers
Element order : Q2-Q2, Q3-Q3 or Q4-Q4.
Any suggestions would be appreciated. I am doing all I can right now to
speed-up matrix assembly, but in general we only need to assemble the matrix
every 3-5 time steps, so I am just trying to find a good compromise between a
good preconditioner that is not crazy expensive. Would I be better to accept
having a poorer jacobian matrix, use a more expensive preconditioner and
keeping it for a longer time (say 10-20 time-steps)?
Have you played with the trade-off of having a more expensive preconditioner
but building it less often? For example, using ILU(1) instead of ILU(0), but
only build it every few time steps?
How come you get away with only assembling the matrix every 3-5 time steps?
Are you treating advection explicitly?
I'm also curious about what the matrix you use looks like. It must be
something like
A B
B^T C
What terms are in A,B,C?
Best
Wolfgang
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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