[Core] Incorrect AMGCLSolver::mBlockSize

[matekelemen]

[Core] Incorrect AMGCLSolver::mBlockSize

[AlejandroCornejo]

Wow, that's very interesting (as much as concerning...). I had the same idea about what is the Block size and seems that this piece of code is not workling as expected... I pinned @ddemidov and @RiccardoRossi to be sure about this

[ddemidov]

I am not familiar with Kratos internals well enough to understand what is the problem here, sorry.

[RiccardoRossi]

for (aggregation) AMG to work correctly you need blocks of dofs to be repeated for every node.
let's imagine that we have dx dy dz to be the displacements

if we have

dx_1 dy_1 dz_1 dx_2 dy_2 dz_2 dx_3 dy_3 dz_3

than all of the nodes 1 2 and 3 have the same anount of dofs. 3 in this case.

however if you have for example

dx_1 dy_1 dz_1 dx_2 dy_2 dx_3 dy_3 dz_3

that is, for example if 2 does not have "dz" in the system, BlockSize will be detected as 1 as it is the only multiplier we have

the "BlockBuilderAndSolver" ensures that this property is kept. The Eliminiation builder and solver does not ...

to be clear, if you have a multidimensional problem (like structures) and the BlockSize==1 aggregation multigrid will NOT work correctly. You could still use RugenStuben for example, but aggregation based amg will not work properly

[dcagritan]

Do we have documentation regarding solvers in Kratos? Documentation or a wiki page that explains the parameters of the solvers for instance?

[RiccardoRossi]

no El vie., 1 dic. 2023 16:21, Deniz Tanyildiz ***@***.***> escribió:

…

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