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[Getfem-users] Imposing Dirichlet boundary conditions with lagrangian mu
From: |
GUILMIN Anne-Lise |
Subject: |
[Getfem-users] Imposing Dirichlet boundary conditions with lagrangian multipliers |
Date: |
Mon, 12 Apr 2010 19:07:52 +0200 |
Dear
all,
First,
thank you for developping this library. It is such a
pleasure to write a finite element code without bothering (too much) about
indices !
I want
to impose normal Dirichlet conditions so I define multipliers and use
a hand-made brick to fill the matrix and the right hand
side.
My
problem is that I don't get the right number of lagragian multipliers. It seems
to be linked with the add_multiplier
function.
I send
you a modified version of the getfem test elastostatic.cc to
underline this problem. In this one, normal Dirichlet conditions are imposed on
the bottom and lateral faces of the mesh.
The
following results are given for a linear quadrilateral two-dimensionnal
single element : a square with 4 nodes.
When
defining the multipliers with add_fem_variable (line 589), we
get the right number of lagragian multipliers : 2 on each imposed face =
6.
When
defining the multipliers with add_multiplier instead (line
591), we get less multipliers than expected : only 1 on two faces and 2 on the
last >
It
acts as if no boundary condition was imposed on the bottom left
node.
If I
understood well, when using the add_multiplier definition, we
start creating multipliers on the whole mesh, then we fill the matrix part
dedicated to Dirichlet boundary conditions and finally we simplify it to
eliminate useless lines and columns (step which is necessary for Gaussian
elimination). Could there be a problem in the way that the matrix is
simplified which would explain the disappearance of some useful
multipliers?
If
not, what should I do to get the right number of multipliers using
add_multiplier?
I
would be thankful for any help or explanation.
Best
regards,
Anne-Lise Guilmin
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elastostatic.tar.gz
Description: elastostatic.tar.gz
- [Getfem-users] Imposing Dirichlet boundary conditions with lagrangian multipliers,
GUILMIN Anne-Lise <=