On Mon, Jul 8, 2024 at 6:14 AM Miguel Angel Salazar de Troya < miguel.sala...@corintis.com> wrote:
> Thanks Adam and Matt, > > Matt, can I get away with just using PCFIELDSPLIT? Or do I need the > SNESFIELDSPLIT? Though it looks like the block Gauss-Seidel is only > implemented in serial ( > https://urldefense.us/v3/__https://petsc.org/main/manual/ksp/*block-jacobi-and-overlapping-additive-schwarz-preconditioners__;Iw!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_GnSYekO$ > > ) > You can do what you want for the linear problem, but that will probably not help. The best thing I know of for this kind of nonlinear coupling is now called primal-dual Newton, a name which I am not wild about. It is discussed here (https://urldefense.us/v3/__https://core.ac.uk/download/pdf/211337815.pdf__;!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_DT_42uJ$ ) and originated in reference [33] from that thesis. My aim was to allow these kinds of solvers with that branch. > On a more theoretical note, I have the impression that the convergence > failures of the Newton-Raphson method for this kind of problem is > ultimately due to a lack of a diagonally dominant Jacobian. I have not > found any reference so I might be wrong. > I would say that the dominant direction for momentum hides the direction for improvement of the coefficient. Thanks, Matt > Best, > Miguel > > On Sat, Jul 6, 2024 at 3:33 PM Matthew Knepley <knep...@gmail.com> wrote: > >> On Fri, Jul 5, 2024 at 3:29 AM Miguel Angel Salazar de Troya < >> miguel.sala...@corintis.com> wrote: >> >>> Hello, I have the Navier-Stokes equation coupled with a >>> convection-diffusion equation for the temperature. It is a two-way coupling >>> because the viscosity depends on the temperature. One way to solve this is >>> with some kind of fixed point iteration >>> ZjQcmQRYFpfptBannerStart >>> This Message Is From an External Sender >>> This message came from outside your organization. >>> >>> ZjQcmQRYFpfptBannerEnd >>> Hello, >>> >>> I have the Navier-Stokes equation coupled with a convection-diffusion >>> equation for the temperature. It is a two-way coupling because the >>> viscosity depends on the temperature. One way to solve this is with some >>> kind of fixed point iteration scheme, where I solve each equation >>> separately in a loop until I see convergence. I am aware this is not >>> possible directly at the SNES level. Is there something that one can do >>> using PCFIELDSPLIT? I would like to assemble my fully coupled system and >>> play with the solver options to get some kind of fixed-point iteration >>> scheme. I would like to avoid having to build two separate SNES solvers, >>> one per equation. Any reference on techniques to solve this type of coupled >>> system is welcome. >>> >> >> Hi Miguel, >> >> I have a branch >> >> >> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/tree/knepley/feature-snes-fieldsplit?ref_type=heads__;!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_ESUOIOo$ >> >> >> that will allow you to do exactly what you want to do. However, there are >> caveats. In order to have SNES do this, it needs a way to selectively >> reassemble subproblems. I assume you are using Firedrake, so this will >> not work. I would definitely be willing to work with those guys to get >> this going, introducing callbacks, just as we did on the FieldSplit case. >> >> Thanks, >> >> Matt >> >> >>> Best, >>> Miguel >>> >> >> >> -- >> What most experimenters take for granted before they begin their >> experiments is infinitely more interesting than any results to which their >> experiments lead. >> -- Norbert Wiener >> >> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_DKriL_s$ >> >> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_Ne_UeR1$ >> > >> > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_DKriL_s$ <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!eLmDWSrulgDcLMhEC5MITvrmcOrDVcAOy95wwGeNzgl7fvAnsX_ldsB3qVD5ArIV-jCyIHEPt3Po_Ne_UeR1$ >
