[Getdp] Bug in GetDP

Ruth V. Sabariego r.sabariego at ulg.ac.be
Wed Feb 13 10:30:57 CET 2008

You should not include surfaces in a volume domain, that causes the 
problem with the jacobian.
So, the problem is solved when definining your domain as:
    Vol= #{Vbox};
Now, for imposing your potential, you have to include the surfaces in 
the support of the basis function, i.e.:
FunctionSpace {
    { Name fs_vglob ; Type Form0 ; // so we have scalars
        BasisFunction {
            { Name sn ; NameOfCoef vn ; Function BF_Node ;
              Support Region[{Vol, Sbc}] ; Entity NodesOf[ All] ; }
        Constraint {
        { NameOfCoef vn ;
                EntityType NodesOf ; NameOfConstraint 
GlobalElectricPotential ; }

That solves the problem.

tptrsn at ksu.edu wrote:
> Hello,
> while working with GetDP, my major professor found this bug in GetDP.  I
> am wondering if anyone has explanation of this.
> Attached are .geo and .pro filed of the two cases.  In each they are the
> same cube geometry with a simple electrostatics case of a fixed voltage
> on one surface and a Neumann boundary condition specifying grad V on
> the opposing surface.
> In the file appropriately named -works, the side of the cube
> corresponding to the +z face is set to a voltage and the -z face is set
> to grad v = -5.
> This solution runs and provides the expected results of a linear
> gradient of voltage throughout the cube.
> The file named -fails is the exact same problem as the previous example,
> but the surfaces for the boundary conditions have been shifted to the
> opposing faces named the Sright and Sleft.  In this case the program
> returns the following error:
> GetDP   : Error     : Null determinant in 'Get_InverseMatrix'
> By symmetry this is the same problem, we have just turned the cube on
> one side, yet the solution fails and returns the same error message. 
> the combination of the other sides also returns the error message.
> Sincerely,
> Todd Petersen
> Kansas State University
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Dr. Ir. Ruth V. Sabariego
University of Liege, Institut Montefiore,
Dept. of Electrical Engineering & Computer Science, 
Applied & Computational Electromagnetics (ACE),
Sart Tilman Campus, Grande Traverse, 10 (B28), B-4000 LIEGE, Belgium
phone: +32-4-3663737 -- fax: +32-4-3662910 -- http://elap.montefiore.ulg.ac.be/

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