Hi Jean,
Thanks a lot for your response. I am trying as you suggested. I have added
the following code inside the linear solver so that I can get the
eigenvalues at every newton step.
std::vector<std::complex<double>> eigenvalues;
std::vector<Vector<double> > eigenvectors;
SparseMatrix<double> identity (IdentityMatrix(u_dof));
SparseDirectUMFPACK inverse;
inverse.initialize (tangent_matrix.block(u_dof,u_dof));
const int eigensolver_its = static_cast<unsigned int>(
tangent_matrix.block(u_dof, u_dof).m()
* parameters.max_iterations_lin);
SolverControl solver_control(eigensolver_its, 1e-9);
ArpackSolver::ArpackSolver eigensolver(solver_control);
eigensolver.solve(tangent_matrix.block(u_dof,u_dof), identity,
inverse, eigenvalues, eigenvectors);
However, I am getting the follwing error while compiling.
error: ‘ArpackSolver’ has not been declared
I have included the header file #include <deal.II/lac/arpack_solver.h>.
Also, could you please let me know if I have declared the identity matrix
correctly? I am replacing the mass matrix B with the Identity matrix to
compute the eigenvalues and eigenvectors.
Thanks!
Animesh
On Thursday, September 24, 2020 at 1:10:35 AM UTC+5:30 Jean-Paul Pelteret
wrote:
> Hi Animesh,
>
> Although in that code-gallery example the system is assembled into a
> BlockSparseMatrix<double>, the system actually has only one block. So you
> can retrieve the underlying SparseMatrix<double> (and Vector<double> for
> the RHS) via
> tangent_matrix.block(u_dof, u_dof);
> system_rhs.block(u_dof);
> and use them with one of the standard eigensolvers (maybe ArpackSolver
> <https://dealii.org/developer/doxygen/deal.II/classArpackSolver.html>,
> since you want both the eigenvalues and eigenvectors).
>
> I hope that this helps you!
>
> Best,
> Jean-Paul
>
> On 23 Sep 2020, at 20:53, Animesh Rastogi IIT Gandhinagar <
> animesh...@alumni.iitgn.ac.in> wrote:
>
> Hi All,
>
> I am trying to play with the code of Quassi Static Finite Strain
> Compressibility
> <https://dealii.org/developer/doxygen/deal.II/code_gallery_Quasi_static_Finite_strain_Compressible_Elasticity.html>.
>
> I want to calculate the eigenvalues and eigenvectors of the System Tangent
> Matrix (BlockSparseMatrix<double>
> <https://dealii.org/developer/doxygen/deal.II/classBlockSparseMatrix.html>
> tangent_matrix) that we get at every time step after the Newton method has
> converged. However, I could not find any function to calculate the
> eigenvalues and eigenvectors of the BlockSparse Matrix. Could someone
> please help me with this?
>
> Thanks!
>
> AR
>
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