Thanks Barry, I didn't realize you guys had already been in communication, but now that I know that, perhaps I can help him by looking at what you sent.
Randy Barry Smith wrote: > Randy, > > I have sent your user an example of how it may be done sequentially. > We can add support for doing it in parallel but I doubt that his matrix > is big enough to need it (more than say 2000 by 2000). > > Barry > > > On Fri, 21 Sep 2007, Randall Mackie wrote: > >> Matt, >> >> I suspect it is my collegue who asked the earlier questions about >> matrix inverses this week, although I didn't realize that until >> after I sent my original message. >> >> I also suggested he just get the LU factorizations, but he insists >> he needs the actual values to embed in another larger system >> he'll solve. >> >> I suppose that with the LU factorizations, you can just do >> successive solves with a vector with zeros and a 1 in the appropriate >> place to generate the elements you need, no? >> >> I've asked him for more clarification on what he needs exactly. >> >> Thanks, Randy >> >> >> Matthew Knepley wrote: >>> On 9/21/07, Randall Mackie <randy at geosystem.us> wrote: >>>> Matt, >>>> >>>> There may be very valid reasons why one would want a matrix inverse, >>>> say in the context of solving optimizations where you need the >>>> inverse of the covariance matrix, and you need those values to >>>> embed in another system. >>> I do not agree. What are you going to do with the inverse that cannot be >>> done with LU? Backsolves against a matrix are commonplace. >>> >>> Matt >>> >>>> In this case, just getting the action of the inverse times a vector >>>> is not what is needed. >>>> >>>> Randy >>>> >>>> >>>> Matthew Knepley wrote: >>>>> On 9/21/07, Randall Mackie <randy at geosystem.us> wrote: >>>>>> I have a collegue who is considering to use PETSc for programming >>>>>> his problem. He would like to know if you can get the actual >>>>>> inverse of a matrix, because this inverse is embedded in another >>>>>> larger system that is then solved. >>>>>> >>>>>> I suppose that if you solve the system directly, say with SuperLU >>>>>> or MUMPS, you could get the actual inverse? I looked briefly through >>>>>> the manual and documentation, but it didn't jump out at me. >>>>> This makes several time this week people have asked for inverses. Never >>>>> never never use the inverse. Its not stable. The storage blows up. That >>>>> is >>>>> why factorizations were invented. Numerical analysis courses have failed >>>>> the country entirely. Just use a KSP and tell it -ksp_type preonly >>>>> -pc_type lu >>>>> and then you can customize the matrix type for different solvers. >>>>> KSPSolve() >>>>> will apply the matrix. If you want to get the action on an entire >>>>> matrix, this >>>>> is dense and we would have to put in the BLAS3 triangular solve calls. >>>>> >>>>> Matt >>>>> >>>>>> Any advice here? >>>>>> >>>>>> Thanks, Randy >>>>>> >>>>>> -- >>>>>> Randall Mackie >>>>>> GSY-USA, Inc. >>>>>> PMB# 643 >>>>>> 2261 Market St., >>>>>> San Francisco, CA 94114-1600 >>>>>> Tel (415) 469-8649 >>>>>> Fax (415) 469-5044 >>>>>> >>>>>> California Registered Geophysicist >>>>>> License No. GP 1034 >>>>>> >>>>>> >>>> -- >>>> Randall Mackie >>>> GSY-USA, Inc. >>>> PMB# 643 >>>> 2261 Market St., >>>> San Francisco, CA 94114-1600 >>>> Tel (415) 469-8649 >>>> Fax (415) 469-5044 >>>> >>>> California Registered Geophysicist >>>> License No. GP 1034 >>>> >>>> >>> >> > -- Randall Mackie GSY-USA, Inc. PMB# 643 2261 Market St., San Francisco, CA 94114-1600 Tel (415) 469-8649 Fax (415) 469-5044 California Registered Geophysicist License No. GP 1034
