[petsc-users] Testing DMPlex new functionalities

[Luc Berger-Vergiat]

Ok, I think what I will do is the following:

void top_bc(const PetscReal x[], PetscScalar *u, void *ctx)
{
   *u = 0.2;
}
void bottom_bc(const PetscReal x[], PetscScalar *u, void *ctx)
{
   *u = 0.0;
}


ierr = DMPlexAddBoundary(dm, PETSC_TRUE,"bottom","Face Sets",0,(void 
(*)())bottom_bc,1,ids[0],&user);CHKERRQ(ierr);
ierr = DMPlexAddBoundary(dm, PETSC_TRUE,"top","Face Sets",0,(void 
(*)())top_bc,1,ids[1],&user);CHKERRQ(ierr);

Matt, have you started writing some documentation for these function?
If not I could probably get something started since I'm reading them.

Another question, how do I explain to my DMPlex that I am solving an 
elasticity problem and hence my solution field will be a 2 components 
vector and not a scalar? I haven't seen where you set this info in snes 
example 12...

Best,
Luc

On 01/22/2015 05:19 PM, Matthew Knepley wrote:
> On Thu, Jan 22, 2015 at 4:17 PM, Luc Berger-Vergiat 
> <lb2653 at columbia.edu <mailto:lb2653 at columbia.edu>> wrote:
>
>     Yes you are right, I corrected for the machine epsilon.
>     I also looked deeper in Petsc's source code and I think I
>     understand better how you implemented the GMSH reader.
>     For instance the label I really care about is "Face Sets" since it
>     detects automatically the BC's for me.
>     An issue is that "Face Sets" contains 4 strata and I only care
>     about two of these strata.
>     How can I get the names of the Strata and how can I loop over the
>     strata to assign my BCs?
>
>
> Instead of "marker" give "Face Sets"
>
> Instead of 1, give 2
>
> Instead of &id give ids, where PetscInt ids[2] = {stratumValue1, 
> stratumValue2}
>
>   Thanks,
>
>     Matt
>
>     Best,
>     Luc
>
>     On 01/22/2015 05:12 PM, Matthew Knepley wrote:
>>     On Thu, Jan 22, 2015 at 12:08 PM, Luc Berger-Vergiat
>>     <lb2653 at columbia.edu <mailto:lb2653 at columbia.edu>> wrote:
>>
>>         Hi all,
>>         I'm trying to test some functionalities in DMPlex,
>>         specifically I want to do a 2d fem simulation using a mesh
>>         generated by GMSH.
>>         At this point I am trying to understand how Dirichlet BC can
>>         be applied.
>>
>>         Can you explain to me what arguments I have to pass to:
>>         DMPlexAddBoundary()?
>>
>>
>>       ierr = DMPlexAddBoundary(dm, PETSC_TRUE,"wall","marker",(void
>>     (*)())top_displacement,1,&id,user)
>>
>>     PETSC_TRUE means that these unknowns will be eliminated from the
>>     global system
>>
>>     "wall" is the name of the BC
>>
>>     "marker" is the name of the DMLabel that you want to use to
>>     identify the mesh points
>>
>>     1 is the number of label IDs that identify constrained mesh points
>>
>>     id is the label ID which identifies constrained mesh points
>>
>>     top_displacement is the function used to set boundary values
>>
>>         I am attaching a little bit of c code and my mesh.geo and
>>         mesh.msh so that you understand the context.
>>         The BCs I want to apply are displacement of 0.2 in the y
>>         direction if y==1.0
>>         0.0 in the x direction if y==0.0
>>
>>
>>     I might do this:
>>
>>     void top_displacement(const PetscReal x[], PetscScalar *u, void *ctx)
>>     {
>>       *u = x[1] < PETSC_MACHINE_EPSILON ? 0.0 : 0.2;
>>     }
>>
>>       Thanks,
>>
>>          Matt
>>
>>
>>         -- 
>>         Best,
>>         Luc
>>
>>
>>
>>
>>     -- 
>>     What most experimenters take for granted before they begin their
>>     experiments is infinitely more interesting than any results to
>>     which their experiments lead.
>>     -- Norbert Wiener
>
>
>
>
> -- 
> What most experimenters take for granted before they begin their 
> experiments is infinitely more interesting than any results to which 
> their experiments lead.
> -- Norbert Wiener

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