Re: [firedrake] no normal flow Boundary Conditions
Hi Francis, On Tue, 29 Nov 2016 at 04:29 Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Hello,
Some progress since last I wrote:
1) I was able to get the QG linear solver working. I do have a couple of questions though.
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_qg.p...
First, the solver that Jemma and I used for the nonlinear QG code seems to yield the trivial solution. Any idea why that is?
I don't think it's finding a trivial solution. I think that the issue is that you never solve the system. Having set up your linear solver, you are missing: psi_solver.solve() However, the linear solver in your code has another problem. The equation isn't symmetric (the beta*phi*psi.dx(0)*dx term) so CG is unlikely to work. For 2D problems, using a direct solver is usually the right start: solver_parameters={ 'ksp_type':'preonly', 'pc_type':'lu' }
Second, should we be able to use matplotlib to plot the solutions? I was able to get a demo to work but I can't do it for this script.
There are two problems here. The first is that you are calling the plot command from Matplotlib. Unsurprisingly, this does not know about Firedrake Functions. You need to call the Firedrake plot command. p = plot(psi_soln) p.show() However, more importantly, the matplotlib functionality is mostly useful for debugging small systems. Your 50 x 50 mesh is already going to be very slow via this route.
2) The SW problem is not working much better I'm afraid. It does not converge to a solution, which is I suppose better than converging to an incorrect solution. I have a couple of concerns.
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p...
First, i am trying to impose no-normal flow BCs. I am trying to do what I understood Colin suggested but since it's not converging, maybe I misunderstood.
Second, I presume there is a better solver that I should be using?
Same problem as above. You are attempting to use CG for a non-symmetric system. In this case it's a saddle point system. Try using a direct solver instead. Regards, David
Thanks in advance for your help.
Cheers, Francis ------------------ 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 <(519)%20888-4567>
*From:* firedrake-bounces@imperial.ac.uk [firedrake-bounces@imperial.ac.uk] on behalf of Francis Poulin [fpoulin@uwaterloo.ca] *Sent:* Saturday, November 26, 2016 6:54 PM
*To:* firedrake@imperial.ac.uk *Subject:* Re: [firedrake] no normal flow Boundary Conditions Hello,
Minor progress.
I found out that the problem with my QG code was how I imposed the boundary conditions. Now I am happy to say that they both run. Unfortunately, they both give me a zero solution even though the winds are not zero. I plotting the winds and so I know that they're not zero. Maybe I"ll have more luck tomorrow.
Cheers, Francis
------------------ 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 <(519)%20888-4567>
------------------------------ *From:* firedrake-bounces@imperial.ac.uk [firedrake-bounces@imperial.ac.uk] on behalf of Francis Poulin [fpoulin@uwaterloo.ca] *Sent:* Saturday, November 26, 2016 12:58 PM *To:* firedrake@imperial.ac.uk *Subject:* Re: [firedrake] no normal flow Boundary Conditions
Hello again,
Minor update on my wind-driven gyre problem.
I just put together a SW version of the code that solve the Linear Stommel problem. You can find the code in the same github repo,
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p...
To my surprise the solver does not complain, and it is exactly the same thing as in the QG version so maybe that part of it is ok. Unfortunately, the solution seems to be zero. So this code is at least giving me an answer, but a wrong one.
Cheers, Francis
------------------ 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 <(519)%20888-4567>
------------------------------ *From:* firedrake-bounces@imperial.ac.uk [firedrake-bounces@imperial.ac.uk] on behalf of Francis Poulin [fpoulin@uwaterloo.ca] *Sent:* Saturday, November 26, 2016 7:36 AM *To:* firedrake@imperial.ac.uk *Subject:* Re: [firedrake] no normal flow Boundary Conditions
Hello,
Thank you Colin and everyone else for your responses. That was very helpful.
We are working on a bunch of problems right now, both QG and SW. We have many different codes working in FEniCS but I am going to start translating them into Firedrake. Maybe make a demo if people seem interested?
The first code is to solve the Linear Stommel problem in one-layer QG. I was able to translate most of it ok but I seem to be having problems with the solver for some reason. If anyone had any advice on what I am doing wrong that would be greatly appreciated. You can find a link on github
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_qg.p...
After I get this working I will like to solve a variety of other problems. One is the Munk problem, then look at non-linear gyre solutions, then find these solutions in SW.
Cheers, Francis
------------------ 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 <(519)%20888-4567>
------------------------------ *From:* firedrake-bounces@imperial.ac.uk [firedrake-bounces@imperial.ac.uk] on behalf of Colin Cotter [colin.cotter@imperial.ac.uk] *Sent:* Friday, November 25, 2016 4:15 AM *To:* firedrake *Subject:* Re: [firedrake] no normal flow Boundary Conditions
Hi Francis, That depends on the formulation of the equations. If you are using a streamfunction-vorticity formulation as for QG, then you need to set a zero boundary condition for the streamfunction, as a scalar. If you are using a velocity formulation based on H(div) spaces (BDM, RT etc.) then there are only u.n DOFs on the boundary, so setting:
bcs = [DirichletBC(Z.sub(0), Constant((0, 0)), (blah,)), ...
actually only sets the normal component. That's one of the reasons that I like these spaces for GFD.
cheers
--cjc
On 25 November 2016 at 01:17, Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Hello,
Sorry for the bother but I have a simple question to ask.
I am currently developing some code to solve for wind-driven gyres and basin modes using QG and SW. My question is how is it best to impose no-normal flow BCs,
$$\vec u \cdot \hat n = 0$$
for any boundary. I found this in the Navier-Stokes example which says that we should impose zero on particular boundaries. I guess that would work but if one had a more complicated geometry I imagine that would have it's problems.
bcs = [DirichletBC(Z.sub(0), Constant((1, 0)), (4,)), DirichletBC(Z.sub(0), Constant((0, 0)), (1, 2, 3))]
Any suggestions would be greatly appreciated.
Cheers, Francis ------------------ 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
-- http://www.imperial.ac.uk/people/colin.cotter
www.cambridge.org/9781107663916
Hello David, Thanks a lot for the help. Some responses/follow ups below. 1) Sorry that I foolishly forgot to call the solver. That was a pretty silly mistake on my part. 2) Thanks for the advice on what solver to use. That makes a lot of sense. 3) The plot does show up. But it only lasts for a second before it vanishes. Any idea how to get it to last longer? 4) I agree that the SW solver should also be modified to use LU. But at the moment I am using the generic solver and it doesn't converge. I suspect it's because the boundary conditions are not set up correctly. If I wanted to set no-normal flow BCs in my BDM velocity field I am doing the following, The fact that it doesn't converge makes me think that it is not set up correctly. bc = DirichletBC(Z.sub(0), Constant((0, 0)), (1, 2, 3, 4)) Best regards, Francis ------------------ 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 Ham [David.Ham@imperial.ac.uk] Sent: Tuesday, November 29, 2016 4:51 AM To: firedrake Subject: Re: [firedrake] no normal flow Boundary Conditions Hi Francis, On Tue, 29 Nov 2016 at 04:29 Francis Poulin <fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca>> wrote: Hello, Some progress since last I wrote: 1) I was able to get the QG linear solver working. I do have a couple of questions though. https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_qg.p... First, the solver that Jemma and I used for the nonlinear QG code seems to yield the trivial solution. Any idea why that is? I don't think it's finding a trivial solution. I think that the issue is that you never solve the system. Having set up your linear solver, you are missing: psi_solver.solve() However, the linear solver in your code has another problem. The equation isn't symmetric (the beta*phi*psi.dx(0)*dx term) so CG is unlikely to work. For 2D problems, using a direct solver is usually the right start: solver_parameters={ 'ksp_type':'preonly', 'pc_type':'lu' } Second, should we be able to use matplotlib to plot the solutions? I was able to get a demo to work but I can't do it for this script. There are two problems here. The first is that you are calling the plot command from Matplotlib. Unsurprisingly, this does not know about Firedrake Functions. You need to call the Firedrake plot command. p = plot(psi_soln) p.show() However, more importantly, the matplotlib functionality is mostly useful for debugging small systems. Your 50 x 50 mesh is already going to be very slow via this route. 2) The SW problem is not working much better I'm afraid. It does not converge to a solution, which is I suppose better than converging to an incorrect solution. I have a couple of concerns. https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p... First, i am trying to impose no-normal flow BCs. I am trying to do what I understood Colin suggested but since it's not converging, maybe I misunderstood. Second, I presume there is a better solver that I should be using? Same problem as above. You are attempting to use CG for a non-symmetric system. In this case it's a saddle point system. Try using a direct solver instead. Regards, David Thanks in advance for your help. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca> Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637<tel:(519)%20888-4567> From: firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk> [firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk>] on behalf of Francis Poulin [fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca>] Sent: Saturday, November 26, 2016 6:54 PM To: firedrake@imperial.ac.uk<mailto:firedrake@imperial.ac.uk> Subject: Re: [firedrake] no normal flow Boundary Conditions Hello, Minor progress. I found out that the problem with my QG code was how I imposed the boundary conditions. Now I am happy to say that they both run. Unfortunately, they both give me a zero solution even though the winds are not zero. I plotting the winds and so I know that they're not zero. Maybe I"ll have more luck tomorrow. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca> Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637<tel:(519)%20888-4567> ________________________________ From: firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk> [firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk>] on behalf of Francis Poulin [fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca>] Sent: Saturday, November 26, 2016 12:58 PM To: firedrake@imperial.ac.uk<mailto:firedrake@imperial.ac.uk> Subject: Re: [firedrake] no normal flow Boundary Conditions Hello again, Minor update on my wind-driven gyre problem. I just put together a SW version of the code that solve the Linear Stommel problem. You can find the code in the same github repo, https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p... To my surprise the solver does not complain, and it is exactly the same thing as in the QG version so maybe that part of it is ok. Unfortunately, the solution seems to be zero. So this code is at least giving me an answer, but a wrong one. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca> Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637<tel:(519)%20888-4567> ________________________________ From: firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk> [firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk>] on behalf of Francis Poulin [fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca>] Sent: Saturday, November 26, 2016 7:36 AM To: firedrake@imperial.ac.uk<mailto:firedrake@imperial.ac.uk> Subject: Re: [firedrake] no normal flow Boundary Conditions Hello, Thank you Colin and everyone else for your responses. That was very helpful. We are working on a bunch of problems right now, both QG and SW. We have many different codes working in FEniCS but I am going to start translating them into Firedrake. Maybe make a demo if people seem interested? The first code is to solve the Linear Stommel problem in one-layer QG. I was able to translate most of it ok but I seem to be having problems with the solver for some reason. If anyone had any advice on what I am doing wrong that would be greatly appreciated. You can find a link on github https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_qg.p... After I get this working I will like to solve a variety of other problems. One is the Munk problem, then look at non-linear gyre solutions, then find these solutions in SW. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca> Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637<tel:(519)%20888-4567> ________________________________ From: firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk> [firedrake-bounces@imperial.ac.uk<mailto:firedrake-bounces@imperial.ac.uk>] on behalf of Colin Cotter [colin.cotter@imperial.ac.uk<mailto:colin.cotter@imperial.ac.uk>] Sent: Friday, November 25, 2016 4:15 AM To: firedrake Subject: Re: [firedrake] no normal flow Boundary Conditions Hi Francis, That depends on the formulation of the equations. If you are using a streamfunction-vorticity formulation as for QG, then you need to set a zero boundary condition for the streamfunction, as a scalar. If you are using a velocity formulation based on H(div) spaces (BDM, RT etc.) then there are only u.n DOFs on the boundary, so setting: bcs = [DirichletBC(Z.sub(0), Constant((0, 0)), (blah,)), ... actually only sets the normal component. That's one of the reasons that I like these spaces for GFD. cheers --cjc On 25 November 2016 at 01:17, Francis Poulin <fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca>> wrote: Hello, Sorry for the bother but I have a simple question to ask. I am currently developing some code to solve for wind-driven gyres and basin modes using QG and SW. My question is how is it best to impose no-normal flow BCs, $$\vec u \cdot \hat n = 0$$ for any boundary. I found this in the Navier-Stokes example which says that we should impose zero on particular boundaries. I guess that would work but if one had a more complicated geometry I imagine that would have it's problems. bcs = [DirichletBC(Z.sub(0), Constant((1, 0)), (4,)), DirichletBC(Z.sub(0), Constant((0, 0)), (1, 2, 3))] Any suggestions would be greatly appreciated. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca<mailto:fpoulin@uwaterloo.ca> Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637<tel:%2B1%20519%20888%204567%20x32637> -- http://www.imperial.ac.uk/people/colin.cotter www.cambridge.org/9781107663916<http://www.cambridge.org/9781107663916> [http://assets.cambridge.org/97811076/63916/cover/9781107663916.jpg]
On 29/11/16 13:49, Francis Poulin wrote:
Hello David,
Thanks a lot for the help. Some responses/follow ups below.
1) Sorry that I foolishly forgot to call the solver. That was a pretty silly mistake on my part.
2) Thanks for the advice on what solver to use. That makes a lot of sense.
3) The plot does show up. But it only lasts for a second before it vanishes. Any idea how to get it to last longer?
The plotting we have is designed for interactive use, you can run, for example with ipython: ipython -i my_script.py Then, you'll drop into a prompt when you're done, and you can interact then. See https://ipython.readthedocs.io/en/stable/interactive/plotting.html for how to interact with matplotlib within ipython.
4) I agree that the SW solver should also be modified to use LU. But at the moment I am using the generic solver and it doesn't converge. I suspect it's because the boundary conditions are not set up correctly. If I wanted to set no-normal flow BCs in my BDM velocity field I am doing the following, The fact that it doesn't converge makes me think that it is not set up correctly.
bc = DirichletBC(Z.sub(0), Constant((0, 0)), (1, 2, 3, 4))
If you have a linear problem that is not converging with an iterative method, switching to a direct solve will at least (if that then converges) give you confidence that your formulation is right, you just need to work harder on preconditioning. If the direct solver doesn't work, then you'll want to go back and figure out the problem with your formulation. Lawrence
Hello Lawrence, Thanks for the tip on ipython. That is handy. I have tried using an LU solver and get a PETSc error, Traceback (most recent call last): File "linear_stommel_sw.py", line 57, in <module> sw_solver.solve() File "/home/fpoulin/software/firedrake/src/firedrake/firedrake/variational_solver.py", line 196, in solve self.snes.solve(None, v) File "PETSc/SNES.pyx", line 537, in petsc4py.PETSc.SNES.solve (src/petsc4py.PETSc.c:170683) petsc4py.PETSc.Error: error code 56 [0] SNESSolve() line 4128 in /tmp/pip-SPrpSR-build/src/snes/interface/snes.c [0] SNESSolve_KSPONLY() line 40 in /tmp/pip-SPrpSR-build/src/snes/impls/ksponly/ksponly.c [0] KSPSolve() line 620 in /tmp/pip-SPrpSR-build/src/ksp/ksp/interface/itfunc.c [0] KSPSetUp() line 393 in /tmp/pip-SPrpSR-build/src/ksp/ksp/interface/itfunc.c [0] PCSetUp() line 968 in /tmp/pip-SPrpSR-build/src/ksp/pc/interface/precon.c [0] PCSetUp_LU() line 92 in /tmp/pip-SPrpSR-build/src/ksp/pc/impls/factor/lu/lu.c [0] MatGetOrdering() line 260 in /tmp/pip-SPrpSR-build/src/mat/order/sorder.c [0] MatGetOrdering_ND() line 19 in /tmp/pip-SPrpSR-build/src/mat/order/spnd.c [0] No support for this operation for this object type [0] Cannot get rows for matrix type nest Again, the updated code can be found at the following in case someone wants to look at it. https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p... There is a fenics version of the code that does work that is located in the same directory. https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw_f... Any advice would be greatly appreciated. Best regards, Francis ------------------ 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 Lawrence Mitchell [lawrence.mitchell@imperial.ac.uk] Sent: Tuesday, November 29, 2016 8:55 AM To: firedrake@imperial.ac.uk Subject: Re: [firedrake] no normal flow Boundary Conditions On 29/11/16 13:49, Francis Poulin wrote:
Hello David,
Thanks a lot for the help. Some responses/follow ups below.
1) Sorry that I foolishly forgot to call the solver. That was a pretty silly mistake on my part.
2) Thanks for the advice on what solver to use. That makes a lot of sense.
3) The plot does show up. But it only lasts for a second before it vanishes. Any idea how to get it to last longer?
The plotting we have is designed for interactive use, you can run, for example with ipython: ipython -i my_script.py Then, you'll drop into a prompt when you're done, and you can interact then. See https://ipython.readthedocs.io/en/stable/interactive/plotting.html for how to interact with matplotlib within ipython.
4) I agree that the SW solver should also be modified to use LU. But at the moment I am using the generic solver and it doesn't converge. I suspect it's because the boundary conditions are not set up correctly. If I wanted to set no-normal flow BCs in my BDM velocity field I am doing the following, The fact that it doesn't converge makes me think that it is not set up correctly.
bc = DirichletBC(Z.sub(0), Constant((0, 0)), (1, 2, 3, 4))
If you have a linear problem that is not converging with an iterative method, switching to a direct solve will at least (if that then converges) give you confidence that your formulation is right, you just need to work harder on preconditioning. If the direct solver doesn't work, then you'll want to go back and figure out the problem with your formulation. Lawrence
On 29 Nov 2016, at 20:56, Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Again, the updated code can be found at the following in case someone wants to look at it.
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p...
Set "mat_type": "aij" In your solver parameters. Lawrence
Thanks Lawrence. That did seem to help. Now I get another errror but now I get that it fails to converge after 0 iterations. It suggests that I add some options. Should I try doing this in firedrake? I am not sure how to use these options but if you think it would help and I can figure out how I am happy to give it a try. Traceback (most recent call last): File "linear_stommel_sw.py", line 58, in <module> sw_solver.solve() File "/home/fpoulin/software/firedrake/src/firedrake/firedrake/variational_solver.py", line 199, in solve solving_utils.check_snes_convergence(self.snes) File "/home/fpoulin/software/firedrake/src/firedrake/firedrake/solving_utils.py", line 153, in check_snes_convergence %s""" % (snes.getIterationNumber(), msg)) firedrake.exceptions.ConvergenceError: Nonlinear solve failed to converge after 0 nonlinear iterations. Reason: Inner linear solve failed to converge after 0 iterations with reason: unknown reason (petsc4py enum incomplete?), try with -snes_convered_reason and -ksp_converged_reason Francis ------------------ 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 Lawrence Mitchell [lawrence.mitchell@imperial.ac.uk] Sent: Tuesday, November 29, 2016 4:15 PM To: firedrake@imperial.ac.uk Subject: Re: [firedrake] no normal flow Boundary Conditions
On 29 Nov 2016, at 20:56, Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Again, the updated code can be found at the following in case someone wants to look at it.
https://github.com/francispoulin/firedrakeQG/blob/master/linear_stommel_sw.p...
Set "mat_type": "aij" In your solver parameters. Lawrence _______________________________________________ firedrake mailing list firedrake@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/firedrake
On 29 Nov 2016, at 21:25, Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Thanks Lawrence.
That did seem to help. Now I get another errror but now I get that it fails to converge after 0 iterations.
It suggests that I add some options. Should I try doing this in firedrake? I am not sure how to use these options but if you think it would help and I can figure out how I am happy to give it a try.
Oh, I should have said. The default LU in petsc does no pivoting and you have a whacking great zero block in your system. Try additionally with: "pc_factor_mat_solver_package": "mumps" The error you saw comes because petsc encountered a zero pivot in the factorisation stage. Lawrence
Excellent! I am happy to say that it not converges to a result, which looks to be the same that I found in fenics. Thanks for all the help! Cheers, Francis ------------------ 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 Lawrence Mitchell [lawrence.mitchell@imperial.ac.uk] Sent: Tuesday, November 29, 2016 4:36 PM To: firedrake@imperial.ac.uk Subject: Re: [firedrake] no normal flow Boundary Conditions
On 29 Nov 2016, at 21:25, Francis Poulin <fpoulin@uwaterloo.ca> wrote:
Thanks Lawrence.
That did seem to help. Now I get another errror but now I get that it fails to converge after 0 iterations.
It suggests that I add some options. Should I try doing this in firedrake? I am not sure how to use these options but if you think it would help and I can figure out how I am happy to give it a try.
Oh, I should have said. The default LU in petsc does no pivoting and you have a whacking great zero block in your system. Try additionally with: "pc_factor_mat_solver_package": "mumps" The error you saw comes because petsc encountered a zero pivot in the factorisation stage. Lawrence _______________________________________________ firedrake mailing list firedrake@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/firedrake
participants (3)
-
David Ham
-
Francis Poulin
-
Lawrence Mitchell