Can you give me any more details about it? thanks. David
On Sun, Mar 7, 2010 at 12:22 PM, Matthew Knepley <knepley at gmail.com> wrote: > On Sun, Mar 7, 2010 at 12:20 PM, David sheehan <david.sheehanjr at > gmail.com>wrote: > >> >I mean Ax =b doesn't have A in explicit form, but in expression >> A=B+C1+C2+...+Cn, >> >where B is main part of A in an explicit form, C1, C2,... and Cn are >> small portions >> >comparing with B and they don't have an explicit form. Thus I want to >> make a >> >preconditioner from B, then apply the preconditioner to Ax=b. Please tell >> me how I >> >can do by PETSC sentences for PETSC solver, thanks. >> >> > call KSPSetOperators(ksp,A,B,......) >> >> However, A doesn't have an explicit matrix form, how to call >> call KSPSetOperators(ksp,A,B,......) >> > > Use MATSHELL for A. > > Matt > > >> ? thanks. >> >> Based on what I thought, once I got preconditioner of B, I am wondering if >> I can >> define a special matrix-vector multiplication for A=B+C1+C2+...+Cn from a >> PETSC >> sentence, such that it can do following >> 1) x1=B*x >> 2) x2=x1+ C1*x, where C1*x is a sequence of matrix-vector multiplications >> 3) x3= x2+C2*x,...... >> ..... >> 4) xn+1=xn+Cn*x,where Cn*x is a squence of matrix-vector multiplications >> >> Then select a KSP iterative method such as GMRES to use the above >> matrix-vector >> multiplication and preconditioner that I made from B. >> >> Could you please tell me if it is possible? if so (I hope), how can I do >> it ? thanks. >> >> David >> >> On Sun, Mar 7, 2010 at 11:12 AM, Barry Smith <bsmith at mcs.anl.gov> wrote: >> >>> >>> On Mar 7, 2010, at 10:57 AM, David sheehan wrote: >>> >>> >First, configure with Hypre . >>> You mean, configure for the installation of PETSC with hypre? thanks. >>> >>> yes, add --download-hypre >>> >>> >>> >Then -pc_type hypre -pc_hypre_type boomeramg >>> You mean, without adding any information into code include, just compile >>> and link >>> the code, to get an excuteable file, e.g. "a.out", then >>> a.out -pc_type hypre -pc_hypre_type boomeramg >>> is it right? thanks. >>> >>> >>> Yes, >>> >>> >>> >I cannot understand exactly what you mean. However, if you want to >>> create a PC >>> > based upon a >matrix which is not the system matrix A, you can specify >>> it in >>> > KSPSetOperators(). >>> >>> I mean Ax =b doesn't have A in explicit form, but in expression >>> A=B+C1+C2+...+Cn, >>> where B is main part of A in an explicity form, C1, C2,... and Cn are >>> small portions >>> comparing with B and they don't have an explicit form. Thus I want to >>> make a >>> preconditioner from B, then apply the preconditioner to Ax=b. Please tell >>> me how I >>> can do by PETSC sentences for PETSC solver, thanks. >>> >>> >>> call KSPSetOperators(ksp,A,B,......) >>> >>> Barry >>> >>> >>> >>> >>> David >>> >>> >>> On Sun, Mar 7, 2010 at 12:32 AM, Matthew Knepley <knepley at >>> gmail.com>wrote: >>> >>>> On Sat, Mar 6, 2010 at 11:49 PM, David sheehan < >>>> david.sheehanjr at gmail.com> wrote: >>>> >>>>> Hi, >>>>> I need your helps about PETSC as follows: >>>>> 1) how can I call boomerAMG of HYPRE through PETSC as a solver and a >>>>> preconditioner? >>>>> >>>> >>>> First, configure with Hypre . Then -pc_type hypre -pc_hypre_type >>>> boomeramg >>>> >>>> >>>>> 2) how can I make a precondioner from B matrix, but apply the >>>>> preconditioner to Ax=b in PETSC? >>>>> Thanks in advance. >>>>> >>>> >>>> I cannot understand exactly what you mean. However, if you want to >>>> create a PC based upon a matrix >>>> which is not the system matrix A, you can specify it in >>>> KSPSetOperators(). >>>> >>>> Matt >>>> >>>> >>>>> David >>>>> >>>> -- >>>> 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 >>>> >>> >>> >>> >> > > > -- > 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20100307/a971a3b8/attachment.html>
