RE: [Libmesh-users] additional degree of freedom

[KIRK, B. (JSC-E. (NASA) <ben...@na...>]

So, your linear system includes some other unknowns that are not associated
with typical nodes or elements?
 
All that really needs to happen is for additional DOFs to get accounted for
in the matrix and vector.  Problem is, as it stands now the DofMap loops
over nodes & elements when it does its indexing.  Sounds like what is needed
is some mechanism to account for "other" DOFs?
 
The quick & dirty way would be to create an additional variable in the
system that is of type, say constant order monomial.  This will give you one
DOF per element to play with.  You can pack your N "global" variables into
the first N elements and then set the remainder to 0 as a standard Dirichlet
constraint.
 
By default the discontinuous DOFs have no implicit coupling with their
neighbors, so the memory penalty for this approach should be minimal.  That
is, the sparse matrix entries for all these additional DOFs should be simply
diagonal.
 
-Ben
 
 
 
  
 
 -----Original Message-----
From: lib...@li...
[mailto:lib...@li...] On Behalf Of Michael
Povolotskyi
Sent: Wednesday, August 10, 2005 7:47 AM
To: lib...@li...
Subject: [Libmesh-users] additional degree of freedom


Dear Libmesh developers,
I 'd like to solve a linear system with Libmesh. The problem is that in
addition to the DOFs that are defined on the mesh, I have to consider some
other variables. These variables are, in some sence, global for the whole
similation domain and can not be connected with a particular node or cell.

So, I have add a new "global" DOF to the system. Is this possible?

Thank you,
Michael.

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