From: [email protected] <[email protected]> Sent: Sunday, June 18, 2023 20:35 To: Duan Junming Cc: [email protected] Subject: Re: [petsc-users] Advice on small block matrix vector multiplication
On Sun, Jun 18, 2023 at 2:13 PM Duan Junming via petsc-users <[email protected]<mailto:[email protected]>> wrote: Dear all, I am using DMPlex to manage the unknowns, two fields, one for pressure, and one for velocities with two/three components, defined in each cell. They're represented by polynomials, with N (10~50) dofs for each component. I have an operator which can be written in a matrix form (N-by-N, dense), to be applied on the pressure field or each component of the velocities in each cell (the same for each cell and also for each component). I was wondering which matrix should be defined to implement the block matrix-vector multiplication, here block means the pressure or the component of the velocities. Maybe a sequential block mat? Could you recommend any example? Or I just implement this matrix-vector multiplication by hand? Dear Matt, Thank you for your quick reply! 1) It sounds like you have a collocated discretization, meaning p,u,v,w are all at the same spots. Is this true? You're right. They're collocated at the same position. 2) You have a dense operator, like FFT, that can act on each component Right, a dense operator applied on each component. 3) I think you should make a vector with blocksize d+1 and extract the components with https://petsc.org/main/manualpages/Vec/VecStrideGather/ then act on them, then restore with https://petsc.org/main/manualpages/Vec/VecStrideScatter/ You can use the *All() versions to do all the components at once. Does this function work with the global/local vector generated from DMPlex? Now the vector is like: p_1, p_2, ..., p_N, u_1, v_1, w_1, ..., u_N, v_N, w_N. Thanks, Matt Thanks! Junming -- 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://www.cse.buffalo.edu/~knepley/<http://www.cse.buffalo.edu/~knepley/>
