September 2021 - petsc-users - mailman3.cels.anl.gov

Re: [petsc-users] Matrix exponential
by Jose E. Roman 05 Sep '21

05 Sep '21

Please always reply to the list (Reply-All), not to myself. You should be able to convert from a scipy sparse matrix to a PETSc matrix via PETSc.Mat().createAIJWithArrays(). Don't know how if there is any example in the petsc4py documentation. Jose > El 3 sept 2021, a las 20:26, Paul, Sanku <paulsank(a)msu.edu> escribió: > > Dear Jose, > > Thank you very much for your help. I have another question can we just simply pass a sparse.csr.matrix to A. For instance, if B is the sparse.csr.matrix can we do A=B.copy(). Or do I have to do it in a different way? > > Best, > Sanku > From: Jose E. Roman <jroman(a)dsic.upv.es> > Sent: Friday, September 3, 2021 2:13 PM > To: Paul, Sanku <paulsank(a)msu.edu> > Cc: petsc-users(a)mcs.anl.gov <petsc-users(a)mcs.anl.gov> > Subject: Re: [petsc-users] Matrix exponential > > You should either create the FN object and then > > E.setFN(F) > > or extract the FN object and assign to a variable > > F = E.getFN() > > You can see an example in $SLEPC_DIR/src/binding/slepc4py/demo/ex6.py > > > Jose > > > > El 3 sept 2021, a las 19:53, Paul, Sanku <paulsank(a)msu.edu> escribió: > > > > Dear Sir/Ma'am, > > > > I am trying to use SLEPc to calculate matrix exponential in my python code but I am not getting the correct result. I have attached the code. Could you let me know what I am doing wrong. This is my first time using SLEPc. So, I would like to ask you if you could send me a tutorial on matrix exponential using SLEPc in python code. > > > > Best, > > Sanku > > <ex2.py>

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Matrix exponential
by Paul, Sanku 03 Sep '21

03 Sep '21

Dear Sir/Ma'am, I am trying to use SLEPc to calculate matrix exponential in my python code but I am not getting the correct result. I have attached the code. Could you let me know what I am doing wrong. This is my first time using SLEPc. So, I would like to ask you if you could send me a tutorial on matrix exponential using SLEPc in python code. Best, Sanku

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Solving subsystem using larger matrix
by Samuel Estes 03 Sep '21

03 Sep '21

Hi, I have a model in which we alternatively solve two submodels by the finite element method both on the same unstructured mesh. The first model (call it model 1) has three degrees of freedom per node while the second model (model 2) is scalar (one degree of freedom). We are trying several different implementations but one option that we would like to try is to use the same matrix for both models. In other words, assuming we have n nodes then we allocate a square matrix A to have 3*n rows, solve model 1, and then reuse this matrix to solve model 2. So for model 2 any non-zeros in the matrix A will be confined to the upper left ninth and the remaining 8/9ths of the matrix are irrelevant to the problem. I have several questions about how best to implement something like this which I will list below: 1. The solver requires that the matrix at least have some non-zeros in each row, otherwise the solution ends up being all NANs. This makes sense as it is solving the subsystem 0*x=0 which is clearly ill-defined. Is there any way that I can communicate to PETSc, either through the solver or matrix classes or some other way, that all I care about is a subsystem and that I would like to use only a portion of the matrix A, the right hand side and the solution vector? There are some routines involving submatrices in the man pages but I'm not sure if they are appropriate for this problem or not. In particular, the MatGetLocalSubMatrix routine might be what I need but its not clear to me whether or not this actually copies the array of values in the submatrix (not desirable due to memory concerns) or if it is just essentially a pointer to the submatrix of values in the original matrix A (ideal). Basically, the idea is to use a part of the matrix that we have without allocating unnecessary extra memory. 2. Is there a way to use multiple local to global mappings for a single matrix. I have a problem when I try to use the same local to global mapping from model 1 in model 2. I understand why this is and can fix it but being able to reset the local to global mapping without destroying the matrix would be an ideal fix. 3. Any other input on the best way to approach solving a problem like this using PETSc would be appreciated. I'm somewhat of a novice when it comes to PETSc so I don't necessarily know all the tools which are available to me. It seems clear that I've reached a point where the manual and man pages aren't quite as helpful as they were for more basic operations. I hope my explanation of the problem and my questions was clear. If not, let me know and I can try to provide more details. Thanks! Sam

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TSBDF info
by Alfredo J Duarte Gomez 02 Sep '21

02 Sep '21

Good morning PETSC team, I am looking to implement a fully implicit BDF-DAE solver and I came across the TSBDF object https://petsc.org/release/src/ts/impls/bdf/bdf.c.html#TSBDF . This seems to be exactly what I am looking for, but I still have questions and I can't seem to find much from it in the documentation or the users manual. The key question for me is whether this is implementation is a *Variable Leading Coefficient BDF *or *Fixed-Leading Coefficient BDF* (such as CVODE). This impacts my ability of reusing matrix factorizations. Thank you, -Alfredo -- Alfredo Duarte Graduate Research Assistant The University of Texas at Austin

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petsc-3.15.4 now available
by Satish Balay 02 Sep '21

02 Sep '21

Dear PETSc users, The patch release petsc-3.15.4 is now available for download. https://petsc.org/release/download/ Satish

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PETSc 3.15.3 compiling error
by Sam Guo 01 Sep '21

01 Sep '21

Dear PETSc dev team, I am compiling petsc 3.15.3 and got following compiling error petsc/src/mat/impls/aij/mpi/mumps/mumps.c:52:31: error: missing binary operator before token "(" 52 | #if PETSC_PKG_MUMPS_VERSION_GE(5,3,0) Any idea what I did wrong? Thanks, Sam

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