Using the subspace iteration method to find modes

[conpierce8]

Hi Peter,

Welcome! dolfinx zeroes the rows and columns of the mass and stiffness matrices corresponding to the Dirichlet dofs and fills the diagonal entries with the optional diagonal keyword argument of assemble_matrix. Hence you get N modes with frequency \sqrt{\frac{K_{diag}}{M_{diag}}}. You can set the diagonal values to appropriately large/small values so that these modes are outside your range of interest:

Modal analysis using dolfin-x

For future visitors to this thread, Here is the script from conpierce8 updated to run on fenicsx circa 2025: # Imports import numpy as np import ufl import sys, slepc4py slepc4py.init(sys.argv) from dolfinx import fem from dolfinx.fem import (Constant, dirichletbc, Function, locate_dofs_topological) from dolfinx.mesh import (create_box, CellType, locate_entities_boundary) from dolfinx.io import XDMFFile from mpi4py import MPI from slepc4py import SLEPc from dolfinx.fem.petsc im…