static char help[] = "Parallel bouncing ball example to test TS event feature.\n";

/*
  The dynamics of the bouncing ball is described by the ODE
                  u1_t = u2
                  u2_t = -9.8

  Each processor is assigned one ball.

  The event function routine checks for the ball hitting the
  ground (u1 = 0). Every time the ball hits the ground, its velocity u2 is attenuated by
  a factor of 0.9 and its height set to 1.0*rank.
*/

#include <petscts.h>

PetscErrorCode EventFunction(TS ts, PetscReal t, Vec U, PetscReal *fvalue, PetscCtx ctx)
{
  const PetscScalar *u;

  PetscFunctionBeginUser;
  /* Event for ball height */
  PetscCall(VecGetArrayRead(U, &u));
  fvalue[0] = PetscRealPart(u[0]);
  PetscCall(VecRestoreArrayRead(U, &u));
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode PostEventFunction(TS ts, PetscInt nevents, PetscInt event_list[], PetscReal t, Vec U, PetscBool forwardsolve, PetscCtx ctx)
{
  PetscScalar *u;
  PetscMPIInt  rank;

  PetscFunctionBeginUser;
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  if (nevents) {
    PetscCall(PetscPrintf(PETSC_COMM_SELF, "Ball hit the ground at t = %5.2f seconds -> Processor[%d]\n", (double)t, rank));
    /* Set new initial conditions with .9 attenuation */
    PetscCall(VecGetArray(U, &u));
    u[0] = 1.0 * rank;
    u[1] = -0.9 * u[1];
    PetscCall(VecRestoreArray(U, &u));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
     Defines the ODE passed to the ODE solver in explicit form: U_t = F(U)
*/
static PetscErrorCode RHSFunction(TS ts, PetscReal t, Vec U, Vec F, PetscCtx ctx)
{
  PetscScalar       *f;
  const PetscScalar *u;

  PetscFunctionBeginUser;
  /*  The next three lines allow us to access the entries of the vectors directly */
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(VecGetArray(F, &f));

  f[0] = u[1];
  f[1] = -9.8;

  PetscCall(VecRestoreArrayRead(U, &u));
  PetscCall(VecRestoreArray(F, &f));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
     Defines the Jacobian of the ODE passed to the ODE solver. See TSSetRHSJacobian() for the meaning the Jacobian.
*/
static PetscErrorCode RHSJacobian(TS ts, PetscReal t, Vec U, Mat A, Mat B, PetscCtx ctx)
{
  PetscInt           rowcol[2], rstart;
  PetscScalar        J[2][2];
  const PetscScalar *u;

  PetscFunctionBeginUser;
  PetscCall(VecGetArrayRead(U, &u));

  PetscCall(MatGetOwnershipRange(B, &rstart, NULL));
  rowcol[0] = rstart;
  rowcol[1] = rstart + 1;

  J[0][0] = 0.0;
  J[0][1] = 1.0;
  J[1][0] = 0.0;
  J[1][1] = 0.0;
  PetscCall(MatSetValues(B, 2, rowcol, 2, rowcol, &J[0][0], INSERT_VALUES));

  PetscCall(VecRestoreArrayRead(U, &u));
  PetscCall(MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY));
  if (A != B) {
    PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
     Defines the ODE passed to the ODE solver in implicit form: F(U_t,U) = 0
*/
static PetscErrorCode IFunction(TS ts, PetscReal t, Vec U, Vec Udot, Vec F, PetscCtx ctx)
{
  PetscScalar       *f;
  const PetscScalar *u, *udot;

  PetscFunctionBeginUser;
  /*  The next three lines allow us to access the entries of the vectors directly */
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(VecGetArrayRead(Udot, &udot));
  PetscCall(VecGetArray(F, &f));

  f[0] = udot[0] - u[1];
  f[1] = udot[1] + 9.8;

  PetscCall(VecRestoreArrayRead(U, &u));
  PetscCall(VecRestoreArrayRead(Udot, &udot));
  PetscCall(VecRestoreArray(F, &f));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
     Defines the Jacobian of the ODE passed to the ODE solver. See TSSetIJacobian() for the meaning of a and the Jacobian.
*/
static PetscErrorCode IJacobian(TS ts, PetscReal t, Vec U, Vec Udot, PetscReal a, Mat A, Mat B, PetscCtx ctx)
{
  PetscInt           rowcol[2], rstart;
  PetscScalar        J[2][2];
  const PetscScalar *u, *udot;

  PetscFunctionBeginUser;
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(VecGetArrayRead(Udot, &udot));

  PetscCall(MatGetOwnershipRange(B, &rstart, NULL));
  rowcol[0] = rstart;
  rowcol[1] = rstart + 1;

  J[0][0] = a;
  J[0][1] = -1.0;
  J[1][0] = 0.0;
  J[1][1] = a;
  PetscCall(MatSetValues(B, 2, rowcol, 2, rowcol, &J[0][0], INSERT_VALUES));

  PetscCall(VecRestoreArrayRead(U, &u));
  PetscCall(VecRestoreArrayRead(Udot, &udot));

  PetscCall(MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY));
  if (A != B) {
    PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **argv)
{
  TS           ts; /* ODE integrator */
  Vec          U;  /* solution will be stored here */
  PetscMPIInt  rank;
  PetscInt     n = 2;
  PetscScalar *u;
  PetscInt     direction = -1;
  PetscBool    terminate = PETSC_FALSE;
  PetscBool    rhs_form = PETSC_FALSE, hist = PETSC_TRUE;
  TSAdapt      adapt;

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Initialize program
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Create timestepping solver context
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSCreate(PETSC_COMM_WORLD, &ts));
  PetscCall(TSSetType(ts, TSROSW));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set ODE routines
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetProblemType(ts, TS_NONLINEAR));
  /* Users are advised against the following branching and code duplication.
     For problems without a mass matrix like the one at hand, the RHSFunction
     (and companion RHSJacobian) interface is enough to support both explicit
     and implicit timesteppers. This tutorial example also deals with the
     IFunction/IJacobian interface for demonstration and testing purposes. */
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-rhs-form", &rhs_form, NULL));
  if (rhs_form) {
    PetscCall(TSSetRHSFunction(ts, NULL, RHSFunction, NULL));
    PetscCall(TSSetRHSJacobian(ts, NULL, NULL, RHSJacobian, NULL));
  } else {
    PetscCall(TSSetIFunction(ts, NULL, IFunction, NULL));
    PetscCall(TSSetIJacobian(ts, NULL, NULL, IJacobian, NULL));
  }

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set initial conditions
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(VecCreate(PETSC_COMM_WORLD, &U));
  PetscCall(VecSetSizes(U, n, PETSC_DETERMINE));
  PetscCall(VecSetUp(U));
  PetscCall(VecGetArray(U, &u));
  u[0] = 1.0 * rank;
  u[1] = 20.0;
  PetscCall(VecRestoreArray(U, &u));
  PetscCall(TSSetSolution(ts, U));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set solver options
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetSaveTrajectory(ts));
  PetscCall(TSSetMaxTime(ts, 30.0));
  PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_STEPOVER));
  PetscCall(TSSetTimeStep(ts, 0.1));
  /* The adaptive time step controller could take very large timesteps resulting in
     the same event occurring multiple times in the same interval. A maximum step size
     limit is enforced here to avoid this issue. */
  PetscCall(TSGetAdapt(ts, &adapt));
  PetscCall(TSAdaptSetType(adapt, TSADAPTBASIC));
  PetscCall(TSAdaptSetStepLimits(adapt, 0.0, 0.5));

  /* Set direction and terminate flag for the event */
  PetscCall(TSSetEventHandler(ts, 1, &direction, &terminate, EventFunction, PostEventFunction, NULL));

  PetscCall(TSSetFromOptions(ts));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Run timestepping solver
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSolve(ts, U));

  if (hist) { /* replay following history */
    TSTrajectory tj;
    PetscReal    tf, t0, dt;

    PetscCall(TSGetTime(ts, &tf));
    PetscCall(TSSetMaxTime(ts, tf));
    PetscCall(TSSetStepNumber(ts, 0));
    PetscCall(TSRestartStep(ts));
    PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_MATCHSTEP));
    PetscCall(TSSetFromOptions(ts));
    PetscCall(TSSetEventHandler(ts, 1, &direction, &terminate, EventFunction, PostEventFunction, NULL));
    PetscCall(TSGetAdapt(ts, &adapt));
    PetscCall(TSAdaptSetType(adapt, TSADAPTHISTORY));
    PetscCall(TSGetTrajectory(ts, &tj));
    PetscCall(TSAdaptHistorySetTrajectory(adapt, tj, PETSC_FALSE));
    PetscCall(TSAdaptHistoryGetStep(adapt, 0, &t0, &dt));
    /* this example fails with single (or smaller) precision */
#if defined(PETSC_USE_REAL_SINGLE) || defined(PETSC_USE_REAL___FP16)
    PetscCall(TSAdaptSetType(adapt, TSADAPTBASIC));
    PetscCall(TSAdaptSetStepLimits(adapt, 0.0, 0.5));
    PetscCall(TSSetFromOptions(ts));
#endif
    PetscCall(TSSetTime(ts, t0));
    PetscCall(TSSetTimeStep(ts, dt));
    PetscCall(TSResetTrajectory(ts));
    PetscCall(VecGetArray(U, &u));
    u[0] = 1.0 * rank;
    u[1] = 20.0;
    PetscCall(VecRestoreArray(U, &u));
    PetscCall(TSSolve(ts, U));
  }
  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Free work space.  All PETSc objects should be destroyed when they are no longer needed.
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(VecDestroy(&U));
  PetscCall(TSDestroy(&ts));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      suffix: a
      nsize: 2
      args: -ts_trajectory_type memory -snes_stol 1e-4
      filter: sort -b

   test:
      suffix: b
      nsize: 2
      args: -ts_trajectory_type memory -ts_type arkimex -snes_stol 1e-4
      filter: sort -b

   test:
      suffix: c
      nsize: 2
      args: -ts_trajectory_type memory -ts_type theta -ts_adapt_type basic -ts_atol 1e-1 -snes_stol 1e-4
      filter: sort -b

   test:
      suffix: d
      nsize: 2
      args: -ts_trajectory_type memory -ts_type alpha -ts_adapt_type basic -ts_atol 1e-1 -snes_stol 1e-4
      filter: sort -b

   test:
      suffix: e
      nsize: 2
      args: -ts_trajectory_type memory -ts_type bdf -ts_adapt_dt_max 0.015 -ts_max_steps 3000
      filter: sort -b

   test:
      suffix: f
      nsize: 2
      args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 3bs
      filter: sort -b

   test:
      suffix: g
      nsize: 2
      args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 5bs
      filter: sort -b

   test:
      suffix: h
      nsize: 2
      args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 6vr
      filter: sort -b
      output_file: output/ex41_g.out

   test:
      suffix: i
      nsize: 2
      args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 7vr
      filter: sort -b
      output_file: output/ex41_g.out

   test:
      suffix: j
      nsize: 2
      args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 8vr
      filter: sort -b
      output_file: output/ex41_g.out

TEST*/