Re: [Libmesh-users] Elasticity nullspace

[Ataollah M. <am...@ti...>]

Thank Dmitry,

I've seen the implementation in the NonlinearImplicitSystem. I've also made
my own copy of your implementation in
PETScNonlinearSolver::build_mat_null_space inside my own code to do the
same thing for LinearImplicitSystems. I suspect there is something wrong
with the BlockSize since even when I compile libMesh with
enable-blocked-storage the block size for elasticity in 2D (even though I
have 2 variables added) is 1 instead of 2!? The way I understood it was
that if I compile with blocked storage the number of blocks would be equal
to number of variables!

Best,
Ata



On Sat, Jul 19, 2014 at 5:31 PM, Dmitry Karpeyev <ka...@mc...>
wrote:

> Ata,
>
> Note that you can attach a NearNullSpace calculation routine or an
> equivalent callable object to your NonlinearSolver
> (currently supported only for PetscNonlinearSolver, I believe).  The
> solver will detect the NearNullSpace calculator,
> evaluate it and attach the resulting NearNullSpace to the Jacobian.
>
> For the calling sequence see
> class
> NonlinearImplicitSystem::ComputeVectorSubspace::operator()(std::vector<NumericVector<Number>*>&sp,
> sys_type& s)
> Set  NonlinearSolver::nearnullspace to a pointer to a function with the
> same calling sequence as the operator() above.
>
> The (pointers to the) vectors you want to put into sp above have the same
> structure as the solution vector to your NonlinearImplicitSystem.
> In the case of elasticity, for example, you can interpret the vector
> components as nodal displacements if using a Lagrangian basis.
> The easiest way to obtain these vectors is via
> System::add_vector(name,projections=false,parallel_type=GHOSTED).
>
> Hope this helps,
> Dmitry.
>
>
> On Sat, Jul 19, 2014 at 8:45 PM, Ataollah Mesgarnejad <
> am...@ti...> wrote:
>
>> Dear all,
>>
>> I was wondering if there is a way to create the coordinates vector for
>> MatNullSpaceCreateRigidBody? I tried traversing all the nodes in the mesh
>> by doing something like:
>>
>> coords->init (no_nodes*dim, no_local_nodes*dim, false, PARALLEL);
>>
>> coords->zero();
>>
>>  MeshBase::const_node_iterator n = mesh.nodes_begin();
>>
>> const MeshBase::const_node_iterator end_n = mesh.nodes_end();
>>
>>  for (;n!=end_n;++n)
>>
>> {
>>
>> const Node* node = *n;
>>
>> const dof_id_type global_dof_u = node-dof_number(elasticity_system_no,
>> 0,0);
>>
>> const dof_id_type global_dof_v = node-dof_number(elasticity_system_no,
>> 1,0);
>>
>> const dof_id_type global_dof_w = node-dof_number(elasticity_system_no,
>> 2,0);
>>
>>
>>  const Number x = (*node)(0);
>>
>> const Number y = (*node)(1);
>>
>> coords->set(global_dof_u,x);
>>
>> coords->set(global_dof_v,y);
>>
>> const Number z = (*node)(2);
>>
>> coords->set(global_dof_w,z);
>>
>> }
>>
>>
>>
>> with a first order elasticity system (I'm pretty sure the numbering for
>> the
>> variables in elasticity corresponds to those of the PETSc coordinate
>> vector
>> this way).
>>
>> But the Nullspace created by MatNullSpaceCreateRigidBody does not seem to
>> be working (KSP diverges when I set it through KSPSetNullSpace)!!??
>>
>> As always thank you for the help,
>> Ata
>>
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>
>


-- 
A. Mesgarnejad
PhD Student, Research Assistant
Mechanical Engineering Department
Louisiana State University
2203 Patrick F. Taylor Hall
Baton Rouge, La 70803
www.mesgarnejad.com