Hello David, Yes, that is very helpful. Thanks for getting back to me. That is very helpful! I am tried to copy what you've done, see below. But I do have a few questions. 1) Do you have a topetsc function defined like what I have at the top? 2) When you define the petsc matrix, petsc_a, how did you define that? 3) I guess you are solving a regular eigenvalue problem, or is it a generalized eigenvalue problem? If it's in Finite elements i presume it's generalized? In the case of a generalized eigenvalue problem I wonder if I should have es.setOperators(A,M) where A and M are petsc matrices. 4) If yes, then when you have vr, vi = petsc_A.getVec I guess this is solving the eigenvalue problem but should you give it an A and M? Sorry to bother you but I feel like I'm close, just missing an important detail. Cheers, Francis def topetsc(A): A.force_evaluation() return A.petscmat # Set up Eigenvalue Problem: QG Basin modes a = beta*phi*psi.dx(0)*dx m = -inner(grad(psi), grad(phi))*dx - F*psi*phi*dx # Assemble Weak Form into a PETSc Matrix # Impose Boundary Conditions on Mass Matrix A = topetsc(assemble(a)) M = topetsc(assemble(m, bcs=[bc])) # Create solver es = SLEPc.EPS().create(comm=COMM_WORLD) # Set type of eigenvalues es.setWhichEigenpairs(es.Which.SMALLEST_IMAGINARY) # Set number of eigenvalues to compute num_eigenvalues = 5 es.setDimensions(num_eigenvalues) #setting the matrix (petsc_a is a PETSc matrix) es.setOperators(petsc_a) # Fin eigenvalues an eigenvectors vr, vi = petsc_a.getVecs() for i in range(num_eigenvalues): lam = es.getEigenpair(i, vr, vi) eigenvalue[i] = lam.real eigenfunction[i].vector()[:] = vr ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637 ________________________________ From: firedrake-bounces@imperial.ac.uk [firedrake-bounces@imperial.ac.uk] on behalf of David Bernstein [David.Bernstein@meliorinnovations.com] Sent: Wednesday, November 30, 2016 1:26 PM To: firedrake@imperial.ac.uk Subject: Re: [firedrake] eigenvalue problems with SLEPc Hi Francis, I’m working on a project involving a SLEPc eigensolver in Firedrake so I’ve done some of what you mentioned. For instance: creating an eigensolver: es = SLEPc.EPS().create(comm=COMM_WORLD) setting type of eigenvalues: es.setWhichEigenpairs(self.eigensolver.Which.SMALLEST_REAL) setting number of eigenvalues to compute: es.setDimensions(self.num_eigenvalues) setting the matrix (petsc_a is a PETSc matrix) es.setOperators(petsc_a) getting eigenvectors (in my case the eigenvalues are all real, petsc_a is the matrix) vr, vi = petsc_a.getVecs() for i in range(num_eigenvalues): lmbda = es.getEigenpair(i, vr, vi) eigenvalue[i] = lmbda.real eigenfunction[i].vector()[:] = vr Here eigenfunction is an array of Firedrake functions in the right space that has already been allocated. Hope that helps, Dave On Nov 30, 2016, at 2:02 AM, Lawrence Mitchell <lawrence.mitchell@imperial.ac.uk<mailto:lawrence.mitchell@imperial.ac.uk>> wrote: Dear Francis, On 30/11/16 03:23, Francis Poulin wrote: Hello, A while ago someone pointed me towards test_slepc.py for an example on how to solve an eigenvalue problem. I have been using this as a model to compute Quasi-Geostrophic basin modes in a closed basin. We have a version working in FENicS and I am very keen to get it working in Firedrake as well. I have a good start, which can be found on github, https://github.com/francispoulin/firedrakeQG/blob/master/basin_modes_qg.py Unfortunately, I don't know how to do a lot of things. For example specify number of eigenvalues to determine, specify a target eigenvalue, what method to use, or even just look at the eigenvector. Doing this is strictly in the realm of SLEPc, rather than Firedrake itself. We're "just" providing the operators. The SLEPc documentation is therefore probably helpful: http://slepc.upv.es/documentation/manual.htm It describes everything in terms of the C API, but fortunately, slepc4py has somewhat useful documentation strings (type help(some_slepc_function) in ipython). The translation from C functions to slepc4py functions is quite mechanical: EPSFooBar(eps, ...) translates to: eps.fooBar(...) and so forth. Thanks, Lawrence ©Melior Innovations Inc, 2016 all rights reserved. This e-mail is covered by the Electronic Communication Privacy Act, 18 U.S.C. Section 2510-2521 and may be legally privileged. If you have received this transmission in error, please notify the original sender immediately by return e-mail or by telephone at the telephone number provided above and delete/trash the original message from your system. Thank you for your assistance. The information contained herein is confidential information provided only for the use of the individual or entity for whom it was intended. 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