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## [Libmesh-users] Condensing constraints out of system

 [Libmesh-users] Condensing constraints out of system From: James MBewu - 2014-01-27 21:02:59 ```Hi All, Probably a silly question, but is it possible to condense out the rows and columns corresponding to dirichlet boundary conditions so that the resulting system matrix to solve is smaller (using lagrange type elements). I'm using a DirichletBoundary object to apply homogenous constraints to a large number of nodes on the walls of a cylinder and then solving using Petsc, but it doesn't seem to condense out the rows and columns. Is this because it is bad for Petsc and sparsity structure and things (I am using fieldsplit so I guess the arrangement of unknowns is possibly important to Petsc and/or preconditioners)? Would it be easy/useful to implement this myself? Oh yes and I'm solving Navier Stokes with Q2-Q1 elements. Thanks, James ```

 [Libmesh-users] Condensing constraints out of system From: James MBewu - 2014-01-27 21:02:59 ```Hi All, Probably a silly question, but is it possible to condense out the rows and columns corresponding to dirichlet boundary conditions so that the resulting system matrix to solve is smaller (using lagrange type elements). I'm using a DirichletBoundary object to apply homogenous constraints to a large number of nodes on the walls of a cylinder and then solving using Petsc, but it doesn't seem to condense out the rows and columns. Is this because it is bad for Petsc and sparsity structure and things (I am using fieldsplit so I guess the arrangement of unknowns is possibly important to Petsc and/or preconditioners)? Would it be easy/useful to implement this myself? Oh yes and I'm solving Navier Stokes with Q2-Q1 elements. Thanks, James ```