plot eigenmodes using eigs

Question

Hello

I'm solving an eigenvalue problem using "eigs" as i show below

 A=PETScMatrix()
 assemble(a, tensor = A)
 B=PETScMatrix()
 assemble(m, tensor = B)
 A = sp.csr_matrix(A.mat().getValuesCSR()[::-1])
 B = sp.csr_matrix(B.mat().getValuesCSR()[::-1])
 AA=(A+A.T)/2.0 #only to ensure symmetry
 BB=(B+B.T)/2.0 #only to ensure symmetry
 neig=3
 v, VV= eigs(AA, neig, BB, sigma=38.) #v is the eigenvalue, VV eigenvector, sigma is the shift

the examples online show how to solve the problem, but nothing about plotting the eigenmodes. Any suggestion?

Answer 1

Hi,
see the demo here

Once you have eigenvector rx selected from VV you can plot it with following code snippet:

# Initialize function and assign eigenvector
u = Function(V)
u.vector()[:] = rx

# Plot eigenfunction
plot(u)
interactive()

hope it helps.
P.