Date: 2021-03-03T22:27:34+00:00

Actual source code: ex44f.F90
petsc-3.14.5 2021-03-03
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      1:       program main              !   Solves the linear system  J x = f
      2: #include <petsc/finclude/petsc.h>
      3:       use petscksp
      4:       implicit none
      5:       Vec x,f
      6:       Mat J
      7:       DM da
      8:       KSP ksp
      9:       PetscErrorCode ierr
     10:       PetscInt eight,one

     12:       eight = 8
     13:       one = 1
     14:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
     15:       if (ierr .ne. 0) then
     16:         print*,'Unable to initialize PETSc'
     17:         stop
     18:       endif
     19:       call DMDACreate1d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,eight,one,one,PETSC_NULL_INTEGER,da,ierr);CHKERRA(ierr)
     20:       call DMSetFromOptions(da,ierr)
     21:       call DMSetUp(da,ierr)
     22:       call DMCreateGlobalVector(da,x,ierr);CHKERRA(ierr)
     23:       call VecDuplicate(x,f,ierr);CHKERRA(ierr)
     24:       call DMSetMatType(da,MATAIJ,ierr);CHKERRA(ierr)
     25:       call DMCreateMatrix(da,J,ierr);CHKERRA(ierr)

     27:       call ComputeRHS(da,f,ierr);CHKERRA(ierr)
     28:       call ComputeMatrix(da,J,ierr);CHKERRA(ierr)

     30:       call KSPCreate(MPI_COMM_WORLD,ksp,ierr);CHKERRA(ierr)
     31:       call KSPSetOperators(ksp,J,J,ierr);CHKERRA(ierr)
     32:       call KSPSetFromOptions(ksp,ierr);CHKERRA(ierr)
     33:       call KSPSolve(ksp,f,x,ierr);CHKERRA(ierr)

     35:       call MatDestroy(J,ierr);CHKERRA(ierr)
     36:       call VecDestroy(x,ierr);CHKERRA(ierr)
     37:       call VecDestroy(f,ierr);CHKERRA(ierr)
     38:       call KSPDestroy(ksp,ierr);CHKERRA(ierr)
     39:       call DMDestroy(da,ierr);CHKERRA(ierr)
     40:       call PetscFinalize(ierr)
     41:       end

     43: ! AVX512 crashes without this..
     44:       block data init
     45:       implicit none
     46:       PetscScalar sd
     47:       common /cb/ sd
     48:       data sd /0/
     49:       end
     50:       subroutine knl_workarround(xx)
     51:       implicit none
     52:       PetscScalar xx
     53:       PetscScalar sd
     54:       common /cb/ sd
     55:       sd = sd+xx
     56:       end

     58:       subroutine  ComputeRHS(da,x,ierr)
     59:       use petscdmda
     60:       implicit none
     61:       DM da
     62:       Vec x
     63:       PetscErrorCode ierr
     64:       PetscInt xs,xm,i,mx
     65:       PetscScalar hx
     66:       PetscScalar, pointer :: xx(:)
     67:       call DMDAGetInfo(da,PETSC_NULL_INTEGER,mx,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER, &
     68:      &                 PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER, &
     69:      &                 PETSC_NULL_INTEGER,ierr);CHKERRQ(ierr)
     70:       call DMDAGetCorners(da,xs,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,xm,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,ierr);CHKERRQ(ierr)
     71:       hx     = 1.0_PETSC_REAL_KIND/(mx-1)
     72:       call DMDAVecGetArrayF90(da,x,xx,ierr);CHKERRQ(ierr)
     73:       do i=xs,xs+xm-1
     74:         call knl_workarround(xx(i))
     75:         xx(i) = i*hx
     76:       enddo
     77:       call DMDAVecRestoreArrayF90(da,x,xx,ierr);CHKERRQ(ierr)
     78:       return
     79:       end

     81:       subroutine ComputeMatrix(da,J,ierr)
     82:       use petscdm
     83:       use petscmat
     84:       implicit none
     85:       Mat J
     86:       DM da
     87:       PetscErrorCode ierr
     88:       PetscInt xs,xm,i,mx
     89:       PetscScalar hx,one

     91:       one = 1.0
     92:       call DMDAGetInfo(da,PETSC_NULL_INTEGER,mx,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER, &
     93:      &                 PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,   &
     94:      &                 PETSC_NULL_INTEGER,ierr);CHKERRQ(ierr)
     95:       call DMDAGetCorners(da,xs,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,xm,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,ierr);CHKERRQ(ierr)
     96:       hx     = 1.0_PETSC_REAL_KIND/(mx-1)
     97:       do i=xs,xs+xm-1
     98:         if ((i .eq. 0) .or. (i .eq. mx-1)) then
     99:           call MatSetValue(J,i,i,one,INSERT_VALUES,ierr);CHKERRQ(ierr)
    100:         else
    101:           call MatSetValue(J,i,i-1,-hx,INSERT_VALUES,ierr);CHKERRQ(ierr)
    102:           call MatSetValue(J,i,i+1,-hx,INSERT_VALUES,ierr);CHKERRQ(ierr)
    103:           call MatSetValue(J,i,i,2*hx,INSERT_VALUES,ierr);CHKERRQ(ierr)
    104:         endif
    105:       enddo
    106:       call MatAssemblyBegin(J,MAT_FINAL_ASSEMBLY,ierr);CHKERRQ(ierr)
    107:       call MatAssemblyEnd(J,MAT_FINAL_ASSEMBLY,ierr);CHKERRQ(ierr)
    108:       return
    109:       end

    111: !/*TEST
    112: !
    113: !   test:
    114: !      args: -ksp_converged_reason
    115: !
    116: !TEST*/