COMSOL Multiphysics™

femeig
TABLE 1-24: VALID PROPERTY/VALUE PAIRS
PROPERTY VALUES DEFAULT DESCRIPTION
Krylovdim positive integer Dimension of Krylov
space
Neigs positive integer 6 Number of
eigenvalues sought
Out fem | sol | u | lambda | sol
Output variables
stop | solcompdof | Kc |
Dc | Ec | Null | Nnp |
uscale | nullfun |
symmetric
Shift scalar 0 Eigenvalue search
location
In addition, the properties described in the entry femsolver are supported.
Specify where to look for the desired eigenvalues with the property shift. Enter a
real or complex scalar; the default value is 0, meaning that the solver tries to find
eigenvalues close to 0.
Using the property In you can specify explicit values for the matrices in the
eigenvalue problem. The value for this property is a cell array with alternating matrix
names and matrix values. The matrix names can be D, E, K, or N. If the N matrix is
not given, it is taken to be empty. If the D or E matrix is not given, it is taken to be 0.
The property Out defines the output variables and their order. The output fem
means the FEM structure with the solution object fem.sol added. Sol is a femsol
object containing the fields lambda and u. Lambda is a row vector containing the
eigenvalues. U is a solution matrix. Each column in the solution matrix is the solution
vector of the eigenfunction for the corresponding eigenvalue in lambda. The output
value stop returns nonzero if the solution process was not completed. Stop is 1 if
a partial solution was returned, and 2 if no solution was returned. For the other
outputs, see femlin.
For more information about the eigenvalue solver, see “The Eigenvalue/
Eigenfrequency Solver” on page 393 in the COMSOL Multiphysics User’s Guide.
Example
Eigenmodes and Eigenvalues of the L-shaped Membrane
Compute eigenvalues corresponding to eigenmodes for the PDE problem
⎧
⎨
⎩
– ∆u = λu in Ω
u = 0 on ∂Ω
122 | CHAPTER 1: COMMAND REFERENCE