xref: /petsc/src/ts/tutorials/ex15.c (revision 4e8208cbcbc709572b8abe32f33c78b69c819375)

static char help[] = "Time-dependent PDE in 2d. Modified from ex13.c for illustrating how to solve DAEs. \n";
/*
   u_t = uxx + uyy
   0 < x < 1, 0 < y < 1;
   At t=0: u(x,y) = exp(c*r*r*r), if r=PetscSqrtReal((x-.5)*(x-.5) + (y-.5)*(y-.5)) < .125
           u(x,y) = 0.0           if r >= .125

   Boundary conditions:
   Drichlet BC:
   At x=0, x=1, y=0, y=1: u = 0.0

   Neumann BC:
   At x=0, x=1: du(x,y,t)/dx = 0
   At y=0, y=1: du(x,y,t)/dy = 0

   mpiexec -n 2 ./ex15 -da_grid_x 40 -da_grid_y 40 -ts_max_steps 2 -snes_monitor -ksp_monitor
         ./ex15 -da_grid_x 40 -da_grid_y 40  -draw_pause .1 -boundary 1 -ts_monitor_draw_solution
         ./ex15 -da_grid_x 40 -da_grid_y 40  -draw_pause .1 -boundary 1 -Jtype 2 -nstencilpts 9

*/

#include <petscdm.h>
#include <petscdmda.h>
#include <petscts.h>

/*
   User-defined data structures and routines
*/

/* AppCtx: used by FormIFunction() and FormIJacobian() */
typedef struct {
  DM        da;
  PetscInt  nstencilpts; /* number of stencil points: 5 or 9 */
  PetscReal c;
  PetscInt  boundary; /* Type of boundary condition */
  PetscBool viewJacobian;
} AppCtx;

extern PetscErrorCode FormIFunction(TS, PetscReal, Vec, Vec, Vec, void *);
extern PetscErrorCode FormIJacobian(TS, PetscReal, Vec, Vec, PetscReal, Mat, Mat, void *);
extern PetscErrorCode FormInitialSolution(Vec, void *);

int main(int argc, char **argv)
{
  TS        ts;            /* nonlinear solver */
  Vec       u, r;          /* solution, residual vectors */
  Mat       J, Jmf = NULL; /* Jacobian matrices */
  DM        da;
  PetscReal dt;
  AppCtx    user; /* user-defined work context */
  SNES      snes;
  PetscInt  Jtype; /* Jacobian type
                            0: user provide Jacobian;
                            1: slow finite difference;
                            2: fd with coloring; */

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  /* Initialize user application context */
  user.da           = NULL;
  user.nstencilpts  = 5;
  user.c            = -30.0;
  user.boundary     = 0; /* 0: Drichlet BC; 1: Neumann BC */
  user.viewJacobian = PETSC_FALSE;

  PetscCall(PetscOptionsGetInt(NULL, NULL, "-nstencilpts", &user.nstencilpts, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-boundary", &user.boundary, NULL));
  PetscCall(PetscOptionsHasName(NULL, NULL, "-viewJacobian", &user.viewJacobian));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Create distributed array (DMDA) to manage parallel grid and vectors
  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  if (user.nstencilpts == 5) {
    PetscCall(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_STAR, 11, 11, PETSC_DECIDE, PETSC_DECIDE, 1, 1, NULL, NULL, &da));
  } else if (user.nstencilpts == 9) {
    PetscCall(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_BOX, 11, 11, PETSC_DECIDE, PETSC_DECIDE, 1, 1, NULL, NULL, &da));
  } else SETERRQ(PETSC_COMM_WORLD, PETSC_ERR_SUP, "nstencilpts %" PetscInt_FMT " is not supported", user.nstencilpts);
  PetscCall(DMSetFromOptions(da));
  PetscCall(DMSetUp(da));
  user.da = da;

  /*  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Extract global vectors from DMDA;
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(DMCreateGlobalVector(da, &u));
  PetscCall(VecDuplicate(u, &r));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Create timestepping solver context
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSCreate(PETSC_COMM_WORLD, &ts));
  PetscCall(TSSetProblemType(ts, TS_NONLINEAR));
  PetscCall(TSSetType(ts, TSBEULER));
  PetscCall(TSSetDM(ts, da));
  PetscCall(TSSetIFunction(ts, r, FormIFunction, &user));
  PetscCall(TSSetMaxTime(ts, 1.0));
  PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_STEPOVER));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set initial conditions
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(FormInitialSolution(u, &user));
  PetscCall(TSSetSolution(ts, u));
  dt = .01;
  PetscCall(TSSetTimeStep(ts, dt));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Set Jacobian evaluation routine
  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(DMSetMatType(da, MATAIJ));
  PetscCall(DMCreateMatrix(da, &J));
  Jtype = 0;
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-Jtype", &Jtype, NULL));
  if (Jtype == 0) { /* use user provided Jacobian evaluation routine */
    PetscCheck(user.nstencilpts == 5, PETSC_COMM_WORLD, PETSC_ERR_SUP, "user Jacobian routine FormIJacobian() does not support nstencilpts=%" PetscInt_FMT, user.nstencilpts);
    PetscCall(TSSetIJacobian(ts, J, J, FormIJacobian, &user));
  } else { /* use finite difference Jacobian J as preconditioner and '-snes_mf_operator' for Mat*vec */
    PetscCall(TSGetSNES(ts, &snes));
    PetscCall(MatCreateSNESMF(snes, &Jmf));
    if (Jtype == 1) { /* slow finite difference J; */
      PetscCall(SNESSetJacobian(snes, Jmf, J, SNESComputeJacobianDefault, NULL));
    } else if (Jtype == 2) { /* Use coloring to compute  finite difference J efficiently */
      PetscCall(SNESSetJacobian(snes, Jmf, J, SNESComputeJacobianDefaultColor, 0));
    } else SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "Jtype is not supported");
  }

  /*  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Sets various TS parameters from user options
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetFromOptions(ts));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Solve nonlinear system
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSolve(ts, u));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Free work space.
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(MatDestroy(&J));
  PetscCall(MatDestroy(&Jmf));
  PetscCall(VecDestroy(&u));
  PetscCall(VecDestroy(&r));
  PetscCall(TSDestroy(&ts));
  PetscCall(DMDestroy(&da));

  PetscCall(PetscFinalize());
  return 0;
}

/* --------------------------------------------------------------------- */
/*
  FormIFunction = Udot - RHSFunction
*/
PetscErrorCode FormIFunction(TS ts, PetscReal t, Vec U, Vec Udot, Vec F, PetscCtx ctx)
{
  AppCtx     *user = (AppCtx *)ctx;
  DM          da   = user->da;
  PetscInt    i, j, Mx, My, xs, ys, xm, ym;
  PetscReal   hx, hy, sx, sy;
  PetscScalar u, uxx, uyy, **uarray, **f, **udot;
  Vec         localU;

  PetscFunctionBeginUser;
  PetscCall(DMGetLocalVector(da, &localU));
  PetscCall(DMDAGetInfo(da, PETSC_IGNORE, &Mx, &My, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE));

  hx = 1.0 / (PetscReal)(Mx - 1);
  sx = 1.0 / (hx * hx);
  hy = 1.0 / (PetscReal)(My - 1);
  sy = 1.0 / (hy * hy);
  PetscCheck(user->nstencilpts != 9 || hx == hy, PETSC_COMM_WORLD, PETSC_ERR_SUP, "hx must equal hy when nstencilpts = 9 for this example");

  /*
     Scatter ghost points to local vector,using the 2-step process
        DMGlobalToLocalBegin(),DMGlobalToLocalEnd().
     By placing code between these two statements, computations can be
     done while messages are in transition.
  */
  PetscCall(DMGlobalToLocalBegin(da, U, INSERT_VALUES, localU));
  PetscCall(DMGlobalToLocalEnd(da, U, INSERT_VALUES, localU));

  /* Get pointers to vector data */
  PetscCall(DMDAVecGetArrayRead(da, localU, &uarray));
  PetscCall(DMDAVecGetArray(da, F, &f));
  PetscCall(DMDAVecGetArray(da, Udot, &udot));

  /* Get local grid boundaries */
  PetscCall(DMDAGetCorners(da, &xs, &ys, NULL, &xm, &ym, NULL));

  /* Compute function over the locally owned part of the grid */
  for (j = ys; j < ys + ym; j++) {
    for (i = xs; i < xs + xm; i++) {
      /* Boundary conditions */
      if (i == 0 || j == 0 || i == Mx - 1 || j == My - 1) {
        if (user->boundary == 0) { /* Drichlet BC */
          f[j][i] = uarray[j][i];  /* F = U */
        } else {                   /* Neumann BC */
          if (i == 0 && j == 0) {  /* SW corner */
            f[j][i] = uarray[j][i] - uarray[j + 1][i + 1];
          } else if (i == Mx - 1 && j == 0) { /* SE corner */
            f[j][i] = uarray[j][i] - uarray[j + 1][i - 1];
          } else if (i == 0 && j == My - 1) { /* NW corner */
            f[j][i] = uarray[j][i] - uarray[j - 1][i + 1];
          } else if (i == Mx - 1 && j == My - 1) { /* NE corner */
            f[j][i] = uarray[j][i] - uarray[j - 1][i - 1];
          } else if (i == 0) { /* Left */
            f[j][i] = uarray[j][i] - uarray[j][i + 1];
          } else if (i == Mx - 1) { /* Right */
            f[j][i] = uarray[j][i] - uarray[j][i - 1];
          } else if (j == 0) { /* Bottom */
            f[j][i] = uarray[j][i] - uarray[j + 1][i];
          } else if (j == My - 1) { /* Top */
            f[j][i] = uarray[j][i] - uarray[j - 1][i];
          }
        }
      } else { /* Interior */
        u = uarray[j][i];
        /* 5-point stencil */
        uxx = (-2.0 * u + uarray[j][i - 1] + uarray[j][i + 1]);
        uyy = (-2.0 * u + uarray[j - 1][i] + uarray[j + 1][i]);
        if (user->nstencilpts == 9) {
          /* 9-point stencil: assume hx=hy */
          uxx = 2.0 * uxx / 3.0 + (0.5 * (uarray[j - 1][i - 1] + uarray[j - 1][i + 1] + uarray[j + 1][i - 1] + uarray[j + 1][i + 1]) - 2.0 * u) / 6.0;
          uyy = 2.0 * uyy / 3.0 + (0.5 * (uarray[j - 1][i - 1] + uarray[j - 1][i + 1] + uarray[j + 1][i - 1] + uarray[j + 1][i + 1]) - 2.0 * u) / 6.0;
        }
        f[j][i] = udot[j][i] - (uxx * sx + uyy * sy);
      }
    }
  }

  /* Restore vectors */
  PetscCall(DMDAVecRestoreArrayRead(da, localU, &uarray));
  PetscCall(DMDAVecRestoreArray(da, F, &f));
  PetscCall(DMDAVecRestoreArray(da, Udot, &udot));
  PetscCall(DMRestoreLocalVector(da, &localU));
  PetscCall(PetscLogFlops(11.0 * ym * xm));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/* --------------------------------------------------------------------- */
/*
  FormIJacobian() - Compute IJacobian = dF/dU + a dF/dUdot
  This routine is not used with option '-use_coloring'
*/
PetscErrorCode FormIJacobian(TS ts, PetscReal t, Vec U, Vec Udot, PetscReal a, Mat J, Mat Jpre, PetscCtx ctx)
{
  PetscInt    i, j, Mx, My, xs, ys, xm, ym, nc;
  AppCtx     *user = (AppCtx *)ctx;
  DM          da   = user->da;
  MatStencil  col[5], row;
  PetscScalar vals[5], hx, hy, sx, sy;

  PetscFunctionBeginUser;
  PetscCall(DMDAGetInfo(da, PETSC_IGNORE, &Mx, &My, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE));
  PetscCall(DMDAGetCorners(da, &xs, &ys, NULL, &xm, &ym, NULL));

  hx = 1.0 / (PetscReal)(Mx - 1);
  sx = 1.0 / (hx * hx);
  hy = 1.0 / (PetscReal)(My - 1);
  sy = 1.0 / (hy * hy);

  for (j = ys; j < ys + ym; j++) {
    for (i = xs; i < xs + xm; i++) {
      nc    = 0;
      row.j = j;
      row.i = i;
      if (user->boundary == 0 && (i == 0 || i == Mx - 1 || j == 0 || j == My - 1)) {
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 1.0;

      } else if (user->boundary > 0 && i == 0) { /* Left Neumann */
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 1.0;
        col[nc].j  = j;
        col[nc].i  = i + 1;
        vals[nc++] = -1.0;
      } else if (user->boundary > 0 && i == Mx - 1) { /* Right Neumann */
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 1.0;
        col[nc].j  = j;
        col[nc].i  = i - 1;
        vals[nc++] = -1.0;
      } else if (user->boundary > 0 && j == 0) { /* Bottom Neumann */
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 1.0;
        col[nc].j  = j + 1;
        col[nc].i  = i;
        vals[nc++] = -1.0;
      } else if (user->boundary > 0 && j == My - 1) { /* Top Neumann */
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 1.0;
        col[nc].j  = j - 1;
        col[nc].i  = i;
        vals[nc++] = -1.0;
      } else { /* Interior */
        col[nc].j  = j - 1;
        col[nc].i  = i;
        vals[nc++] = -sy;
        col[nc].j  = j;
        col[nc].i  = i - 1;
        vals[nc++] = -sx;
        col[nc].j  = j;
        col[nc].i  = i;
        vals[nc++] = 2.0 * (sx + sy) + a;
        col[nc].j  = j;
        col[nc].i  = i + 1;
        vals[nc++] = -sx;
        col[nc].j  = j + 1;
        col[nc].i  = i;
        vals[nc++] = -sy;
      }
      PetscCall(MatSetValuesStencil(Jpre, 1, &row, nc, col, vals, INSERT_VALUES));
    }
  }
  PetscCall(MatAssemblyBegin(Jpre, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(Jpre, MAT_FINAL_ASSEMBLY));
  if (J != Jpre) {
    PetscCall(MatAssemblyBegin(J, MAT_FINAL_ASSEMBLY));
    PetscCall(MatAssemblyEnd(J, MAT_FINAL_ASSEMBLY));
  }

  if (user->viewJacobian) {
    PetscCall(PetscPrintf(PetscObjectComm((PetscObject)Jpre), "Jpre:\n"));
    PetscCall(MatView(Jpre, PETSC_VIEWER_STDOUT_WORLD));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

/* ------------------------------------------------------------------- */
PetscErrorCode FormInitialSolution(Vec U, void *ptr)
{
  AppCtx       *user = (AppCtx *)ptr;
  DM            da   = user->da;
  PetscReal     c    = user->c;
  PetscInt      i, j, xs, ys, xm, ym, Mx, My;
  PetscScalar **u;
  PetscReal     hx, hy, x, y, r;

  PetscFunctionBeginUser;
  PetscCall(DMDAGetInfo(da, PETSC_IGNORE, &Mx, &My, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE, PETSC_IGNORE));

  hx = 1.0 / (PetscReal)(Mx - 1);
  hy = 1.0 / (PetscReal)(My - 1);

  /* Get pointers to vector data */
  PetscCall(DMDAVecGetArray(da, U, &u));

  /* Get local grid boundaries */
  PetscCall(DMDAGetCorners(da, &xs, &ys, NULL, &xm, &ym, NULL));

  /* Compute function over the locally owned part of the grid */
  for (j = ys; j < ys + ym; j++) {
    y = j * hy;
    for (i = xs; i < xs + xm; i++) {
      x = i * hx;
      r = PetscSqrtReal((x - .5) * (x - .5) + (y - .5) * (y - .5));
      if (r < .125) u[j][i] = PetscExpReal(c * r * r * r);
      else u[j][i] = 0.0;
    }
  }

  /* Restore vectors */
  PetscCall(DMDAVecRestoreArray(da, U, &u));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*TEST

    test:
      args: -da_grid_x 20 -da_grid_y 20 -boundary 0 -ts_max_steps 10 -ts_monitor

    test:
      suffix: 2
      args: -da_grid_x 20 -da_grid_y 20 -boundary 0 -ts_max_steps 10 -Jtype 2 -ts_monitor

    test:
      suffix: 3
      requires: !single
      args: -da_grid_x 20 -da_grid_y 20 -boundary 1 -ts_max_steps 10 -ts_monitor

    test:
      suffix: 4
      requires: !single
      nsize: 2
      args: -da_grid_x 20 -da_grid_y 20 -boundary 1 -ts_max_steps 10 -ts_monitor

    test:
      suffix: 5
      nsize: 1
      args: -da_grid_x 20 -da_grid_y 20 -boundary 0 -ts_max_steps 10 -Jtype 1 -ts_monitor

TEST*/