xref: /petsc/src/ts/tutorials/ex45.c (revision 4e8208cbcbc709572b8abe32f33c78b69c819375)

static char help[] = "Heat Equation in 2d and 3d with finite elements.\n\
We solve the heat equation in a rectangular\n\
domain, using a parallel unstructured mesh (DMPLEX) to discretize it.\n\
Contributed by: Julian Andrej <juan@tf.uni-kiel.de>\n\n\n";

#include <petscdmplex.h>
#include <petscds.h>
#include <petscts.h>

/*
  Heat equation:

    du/dt - \Delta u + f = 0
*/

typedef enum {
  SOL_QUADRATIC_LINEAR,
  SOL_QUADRATIC_TRIG,
  SOL_TRIG_LINEAR,
  SOL_TRIG_TRIG,
  NUM_SOLUTION_TYPES
} SolutionType;
const char *solutionTypes[NUM_SOLUTION_TYPES + 1] = {"quadratic_linear", "quadratic_trig", "trig_linear", "trig_trig", "unknown"};

typedef struct {
  SolutionType solType; /* Type of exact solution */
  /* Solver setup */
  PetscBool expTS;        /* Flag for explicit timestepping */
  PetscBool lumped;       /* Lump the mass matrix */
  PetscInt  remesh_every; /* Remesh every number of steps */
  DM        remesh_dm;    /* New DM after remeshing */
} AppCtx;

/*
Exact 2D solution:
  u    = 2t + x^2 + y^2
  u_t  = 2
  \Delta u = 2 + 2 = 4
  f    = 2
  F(u) = 2 - (2 + 2) + 2 = 0

Exact 3D solution:
  u = 3t + x^2 + y^2 + z^2
  F(u) = 3 - (2 + 2 + 2) + 3 = 0
*/
static PetscErrorCode mms_quad_lin(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  PetscInt d;

  *u = dim * time;
  for (d = 0; d < dim; ++d) *u += x[d] * x[d];
  return PETSC_SUCCESS;
}

static PetscErrorCode mms_quad_lin_t(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  *u = dim;
  return PETSC_SUCCESS;
}

static void f0_quad_lin_exp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  f0[0] = -(PetscScalar)dim;
}
static void f0_quad_lin(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  PetscScalar exp[1] = {0.};
  f0_quad_lin_exp(dim, Nf, NfAux, uOff, uOff_x, u, u_t, u_x, aOff, aOff_x, a, a_t, a_x, t, x, numConstants, constants, exp);
  f0[0] = u_t[0] - exp[0];
}

/*
Exact 2D solution:
  u = 2*cos(t) + x^2 + y^2
  F(u) = -2*sint(t) - (2 + 2) + 2*sin(t) + 4 = 0

Exact 3D solution:
  u = 3*cos(t) + x^2 + y^2 + z^2
  F(u) = -3*sin(t) - (2 + 2 + 2) + 3*sin(t) + 6 = 0
*/
static PetscErrorCode mms_quad_trig(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  PetscInt d;

  *u = dim * PetscCosReal(time);
  for (d = 0; d < dim; ++d) *u += x[d] * x[d];
  return PETSC_SUCCESS;
}

static PetscErrorCode mms_quad_trig_t(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  *u = -dim * PetscSinReal(time);
  return PETSC_SUCCESS;
}

static void f0_quad_trig_exp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  f0[0] = -dim * (PetscSinReal(t) + 2.0);
}
static void f0_quad_trig(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  PetscScalar exp[1] = {0.};
  f0_quad_trig_exp(dim, Nf, NfAux, uOff, uOff_x, u, u_t, u_x, aOff, aOff_x, a, a_t, a_x, t, x, numConstants, constants, exp);
  f0[0] = u_t[0] - exp[0];
}

/*
Exact 2D solution:
  u = 2\pi^2 t + cos(\pi x) + cos(\pi y)
  F(u) = 2\pi^2 - \pi^2 (cos(\pi x) + cos(\pi y)) + \pi^2 (cos(\pi x) + cos(\pi y)) - 2\pi^2 = 0

Exact 3D solution:
  u = 3\pi^2 t + cos(\pi x) + cos(\pi y) + cos(\pi z)
  F(u) = 3\pi^2 - \pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z)) + \pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z)) - 3\pi^2 = 0
*/
static PetscErrorCode mms_trig_lin(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  PetscInt d;

  *u = dim * PetscSqr(PETSC_PI) * time;
  for (d = 0; d < dim; ++d) *u += PetscCosReal(PETSC_PI * x[d]);
  return PETSC_SUCCESS;
}

static PetscErrorCode mms_trig_lin_t(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  *u = dim * PetscSqr(PETSC_PI);
  return PETSC_SUCCESS;
}

static void f0_trig_lin(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  PetscInt d;
  f0[0] = u_t[0];
  for (d = 0; d < dim; ++d) f0[0] += PetscSqr(PETSC_PI) * (PetscCosReal(PETSC_PI * x[d]) - 1.0);
}

/*
Exact 2D solution:
  u    = pi^2 cos(t) + cos(\pi x) + cos(\pi y)
  u_t  = -pi^2 sin(t)
  \Delta u = -\pi^2 (cos(\pi x) + cos(\pi y))
  f    = pi^2 sin(t) - \pi^2 (cos(\pi x) + cos(\pi y))
  F(u) = -\pi^2 sin(t) + \pi^2 (cos(\pi x) + cos(\pi y)) - \pi^2 (cos(\pi x) + cos(\pi y)) + \pi^2 sin(t) = 0

Exact 3D solution:
  u    = pi^2 cos(t) + cos(\pi x) + cos(\pi y) + cos(\pi z)
  u_t  = -pi^2 sin(t)
  \Delta u = -\pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z))
  f    = pi^2 sin(t) - \pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z))
  F(u) = -\pi^2 sin(t) + \pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z)) - \pi^2 (cos(\pi x) + cos(\pi y) + cos(\pi z)) + \pi^2 sin(t) = 0
*/
static PetscErrorCode mms_trig_trig(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  PetscInt d;

  *u = PetscSqr(PETSC_PI) * PetscCosReal(time);
  for (d = 0; d < dim; ++d) *u += PetscCosReal(PETSC_PI * x[d]);
  return PETSC_SUCCESS;
}

static PetscErrorCode mms_trig_trig_t(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt Nc, PetscScalar *u, PetscCtx ctx)
{
  *u = -PetscSqr(PETSC_PI) * PetscSinReal(time);
  return PETSC_SUCCESS;
}

static void f0_trig_trig_exp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  PetscInt d;
  f0[0] -= PetscSqr(PETSC_PI) * PetscSinReal(t);
  for (d = 0; d < dim; ++d) f0[0] += PetscSqr(PETSC_PI) * PetscCosReal(PETSC_PI * x[d]);
}
static void f0_trig_trig(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f0[])
{
  PetscScalar exp[1] = {0.};
  f0_trig_trig_exp(dim, Nf, NfAux, uOff, uOff_x, u, u_t, u_x, aOff, aOff_x, a, a_t, a_x, t, x, numConstants, constants, exp);
  f0[0] = u_t[0] - exp[0];
}

static void f1_temp_exp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f1[])
{
  for (PetscInt d = 0; d < dim; ++d) f1[d] = -u_x[d];
}
static void f1_temp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f1[])
{
  for (PetscInt d = 0; d < dim; ++d) f1[d] = u_x[d];
}

static void g3_temp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g3[])
{
  for (PetscInt d = 0; d < dim; ++d) g3[d * dim + d] = 1.0;
}

static void g0_temp(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g0[])
{
  g0[0] = u_tShift * 1.0;
}

static PetscErrorCode ProcessOptions(MPI_Comm comm, AppCtx *options)
{
  PetscInt sol;

  PetscFunctionBeginUser;
  options->solType      = SOL_QUADRATIC_LINEAR;
  options->expTS        = PETSC_FALSE;
  options->lumped       = PETSC_TRUE;
  options->remesh_every = 0;

  PetscOptionsBegin(comm, "", "Heat Equation Options", "DMPLEX");
  sol = options->solType;
  PetscCall(PetscOptionsEList("-sol_type", "Type of exact solution", "ex45.c", solutionTypes, NUM_SOLUTION_TYPES, solutionTypes[options->solType], &sol, NULL));
  options->solType = (SolutionType)sol;
  PetscCall(PetscOptionsBool("-explicit", "Use explicit timestepping", "ex45.c", options->expTS, &options->expTS, NULL));
  PetscCall(PetscOptionsBool("-lumped", "Lump the mass matrix", "ex45.c", options->lumped, &options->lumped, NULL));
  PetscCall(PetscOptionsInt("-remesh_every", "Remesh every number of steps", "ex45.c", options->remesh_every, &options->remesh_every, NULL));
  PetscOptionsEnd();
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode CreateMesh(MPI_Comm comm, DM *dm, AppCtx *ctx)
{
  PetscFunctionBeginUser;
  PetscCall(DMCreate(comm, dm));
  PetscCall(DMSetType(*dm, DMPLEX));
  PetscCall(DMSetFromOptions(*dm));
  {
    char      convType[256];
    PetscBool flg;
    PetscOptionsBegin(comm, "", "Mesh conversion options", "DMPLEX");
    PetscCall(PetscOptionsFList("-dm_plex_convert_type", "Convert DMPlex to another format", __FILE__, DMList, DMPLEX, convType, 256, &flg));
    PetscOptionsEnd();
    if (flg) {
      DM dmConv;
      PetscCall(DMConvert(*dm, convType, &dmConv));
      if (dmConv) {
        PetscCall(DMDestroy(dm));
        *dm = dmConv;
        PetscCall(DMSetFromOptions(*dm));
        PetscCall(DMSetUp(*dm));
      }
    }
  }
  PetscCall(DMViewFromOptions(*dm, NULL, "-dm_view"));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode SetupProblem(DM dm, AppCtx *ctx)
{
  PetscDS        ds;
  DMLabel        label;
  const PetscInt id = 1;

  PetscFunctionBeginUser;
  PetscCall(DMGetLabel(dm, "marker", &label));
  PetscCall(DMGetDS(dm, &ds));
  PetscCall(PetscDSSetJacobian(ds, 0, 0, g0_temp, NULL, NULL, g3_temp));
  switch (ctx->solType) {
  case SOL_QUADRATIC_LINEAR:
    PetscCall(PetscDSSetResidual(ds, 0, f0_quad_lin, f1_temp));
    PetscCall(PetscDSSetRHSResidual(ds, 0, f0_quad_lin_exp, f1_temp_exp));
    PetscCall(PetscDSSetExactSolution(ds, 0, mms_quad_lin, ctx));
    PetscCall(PetscDSSetExactSolutionTimeDerivative(ds, 0, mms_quad_lin_t, ctx));
    PetscCall(DMAddBoundary(dm, DM_BC_ESSENTIAL, "wall", label, 1, &id, 0, 0, NULL, (PetscVoidFn *)mms_quad_lin, (PetscVoidFn *)mms_quad_lin_t, ctx, NULL));
    break;
  case SOL_QUADRATIC_TRIG:
    PetscCall(PetscDSSetResidual(ds, 0, f0_quad_trig, f1_temp));
    PetscCall(PetscDSSetRHSResidual(ds, 0, f0_quad_trig_exp, f1_temp_exp));
    PetscCall(PetscDSSetExactSolution(ds, 0, mms_quad_trig, ctx));
    PetscCall(PetscDSSetExactSolutionTimeDerivative(ds, 0, mms_quad_trig_t, ctx));
    PetscCall(DMAddBoundary(dm, DM_BC_ESSENTIAL, "wall", label, 1, &id, 0, 0, NULL, (PetscVoidFn *)mms_quad_trig, (PetscVoidFn *)mms_quad_trig_t, ctx, NULL));
    break;
  case SOL_TRIG_LINEAR:
    PetscCall(PetscDSSetResidual(ds, 0, f0_trig_lin, f1_temp));
    PetscCall(PetscDSSetExactSolution(ds, 0, mms_trig_lin, ctx));
    PetscCall(PetscDSSetExactSolutionTimeDerivative(ds, 0, mms_trig_lin_t, ctx));
    PetscCall(DMAddBoundary(dm, DM_BC_ESSENTIAL, "wall", label, 1, &id, 0, 0, NULL, (PetscVoidFn *)mms_trig_lin, (PetscVoidFn *)mms_trig_lin_t, ctx, NULL));
    break;
  case SOL_TRIG_TRIG:
    PetscCall(PetscDSSetResidual(ds, 0, f0_trig_trig, f1_temp));
    PetscCall(PetscDSSetRHSResidual(ds, 0, f0_trig_trig_exp, f1_temp_exp));
    PetscCall(PetscDSSetExactSolution(ds, 0, mms_trig_trig, ctx));
    PetscCall(PetscDSSetExactSolutionTimeDerivative(ds, 0, mms_trig_trig_t, ctx));
    break;
  default:
    SETERRQ(PetscObjectComm((PetscObject)dm), PETSC_ERR_ARG_WRONG, "Invalid solution type: %s (%d)", solutionTypes[PetscMin(ctx->solType, NUM_SOLUTION_TYPES)], ctx->solType);
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode SetupDiscretization(DM dm, AppCtx *ctx)
{
  DM        plex, cdm = dm;
  PetscFE   fe;
  PetscBool simplex;
  PetscInt  dim;

  PetscFunctionBeginUser;
  PetscCall(DMGetDimension(dm, &dim));
  PetscCall(DMConvert(dm, DMPLEX, &plex));
  PetscCall(DMPlexIsSimplex(plex, &simplex));
  PetscCall(DMDestroy(&plex));
  PetscCall(PetscFECreateDefault(PETSC_COMM_SELF, dim, 1, simplex, "temp_", -1, &fe));
  PetscCall(PetscObjectSetName((PetscObject)fe, "temperature"));
  /* Set discretization and boundary conditions for each mesh */
  PetscCall(DMSetField(dm, 0, NULL, (PetscObject)fe));
  PetscCall(DMCreateDS(dm));
  if (ctx->expTS) {
    PetscDS ds;

    PetscCall(DMGetDS(dm, &ds));
    PetscCall(PetscDSSetImplicit(ds, 0, PETSC_FALSE));
  }
  PetscCall(SetupProblem(dm, ctx));
  while (cdm) {
    PetscCall(DMCopyDisc(dm, cdm));
    PetscCall(DMGetCoarseDM(cdm, &cdm));
  }
  PetscCall(PetscFEDestroy(&fe));
  PetscFunctionReturn(PETSC_SUCCESS);
}

#include <petsc/private/dmpleximpl.h>
static PetscErrorCode Remesh(DM dm, Vec U, DM *newdm)
{
  PetscFunctionBeginUser;
  PetscCall(DMViewFromOptions(dm, NULL, "-remesh_dmin_view"));
  *newdm = NULL;

  PetscInt  dim;
  DM        plex;
  PetscBool simplex;
  PetscCall(DMGetDimension(dm, &dim));
  PetscCall(DMConvert(dm, DMPLEX, &plex));
  PetscCall(DMPlexIsSimplex(plex, &simplex));
  PetscCall(DMDestroy(&plex));

  DM      dmGrad;
  PetscFE fe;
  PetscCall(DMClone(dm, &dmGrad));
  PetscCall(PetscFECreateDefault(PETSC_COMM_SELF, dim, dim, simplex, "grad_", -1, &fe));
  PetscCall(DMSetField(dmGrad, 0, NULL, (PetscObject)fe));
  PetscCall(PetscFEDestroy(&fe));
  PetscCall(DMCreateDS(dmGrad));

  Vec locU, locG;
  PetscCall(DMGetLocalVector(dm, &locU));
  PetscCall(DMGetLocalVector(dmGrad, &locG));
  PetscCall(DMGlobalToLocal(dm, U, INSERT_VALUES, locU));
  PetscCall(VecViewFromOptions(locU, NULL, "-remesh_input_view"));
  PetscCall(DMPlexComputeGradientClementInterpolant(dm, locU, locG));
  PetscCall(VecViewFromOptions(locG, NULL, "-remesh_grad_view"));

  const PetscScalar *g;
  PetscScalar       *u;
  PetscInt           n;
  PetscCall(VecGetLocalSize(locU, &n));
  PetscCall(VecGetArrayWrite(locU, &u));
  PetscCall(VecGetArrayRead(locG, &g));
  for (PetscInt i = 0; i < n; i++) {
    PetscReal norm = 0.0;
    for (PetscInt d = 0; d < dim; d++) norm += PetscSqr(PetscRealPart(g[dim * i + d]));
    u[i] = PetscSqrtReal(norm);
  }
  PetscCall(VecRestoreArrayRead(locG, &g));
  PetscCall(VecRestoreArrayWrite(locU, &u));

  DM  dmM;
  Vec metric;
  PetscCall(DMClone(dm, &dmM));
  PetscCall(DMPlexMetricCreateIsotropic(dmM, 0, locU, &metric));
  PetscCall(DMDestroy(&dmM));
  PetscCall(DMRestoreLocalVector(dm, &locU));
  PetscCall(DMRestoreLocalVector(dmGrad, &locG));
  PetscCall(DMDestroy(&dmGrad));

  // TODO remove?
  PetscScalar scale = 10.0;
  PetscCall(PetscOptionsGetScalar(NULL, NULL, "-metric_scale", &scale, NULL));
  PetscCall(VecScale(metric, scale));
  PetscCall(VecViewFromOptions(metric, NULL, "-metric_view"));

  DMLabel label = NULL;
  PetscCall(DMGetLabel(dm, "marker", &label));
  PetscCall(DMAdaptMetric(dm, metric, label, NULL, newdm));
  PetscCall(VecDestroy(&metric));

  PetscCall(DMViewFromOptions(*newdm, NULL, "-remesh_dmout_view"));

  AppCtx *ctx;
  PetscCall(DMGetApplicationContext(dm, &ctx));
  PetscCall(DMSetApplicationContext(*newdm, ctx));
  PetscCall(SetupDiscretization(*newdm, ctx));

  // TODO
  ((DM_Plex *)(*newdm)->data)->useHashLocation = ((DM_Plex *)dm->data)->useHashLocation;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode SetInitialConditions(TS ts, Vec u)
{
  DM        dm;
  PetscReal t;

  PetscFunctionBeginUser;
  PetscCall(TSGetDM(ts, &dm));
  PetscCall(TSGetTime(ts, &t));
  PetscCall(DMComputeExactSolution(dm, t, u, NULL));
  PetscCall(VecSetOptionsPrefix(u, NULL));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode TransferSetUp(TS ts, PetscInt step, PetscReal time, Vec U, PetscBool *remesh, void *tctx)
{
  AppCtx *ctx = (AppCtx *)tctx;

  PetscFunctionBeginUser;
  *remesh = PETSC_FALSE;
  if (ctx->remesh_every > 0 && step && step % ctx->remesh_every == 0) {
    DM dm;

    *remesh = PETSC_TRUE;
    PetscCall(TSGetDM(ts, &dm));
    PetscCall(Remesh(dm, U, &ctx->remesh_dm));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode TransferVecs(TS ts, PetscInt nv, Vec vin[], Vec vout[], void *tctx)
{
  AppCtx *ctx = (AppCtx *)tctx;
  DM      dm;
  Mat     Interp;

  PetscFunctionBeginUser;
  PetscCall(TSGetDM(ts, &dm));
  PetscCall(DMCreateInterpolation(dm, ctx->remesh_dm, &Interp, NULL));
  for (PetscInt i = 0; i < nv; i++) {
    PetscCall(DMCreateGlobalVector(ctx->remesh_dm, &vout[i]));
    PetscCall(MatMult(Interp, vin[i], vout[i]));
  }
  PetscCall(MatDestroy(&Interp));
  PetscCall(TSSetDM(ts, ctx->remesh_dm));
  PetscCall(DMDestroy(&ctx->remesh_dm));
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **argv)
{
  DM     dm;
  TS     ts;
  Vec    u;
  AppCtx ctx;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCall(ProcessOptions(PETSC_COMM_WORLD, &ctx));
  PetscCall(CreateMesh(PETSC_COMM_WORLD, &dm, &ctx));
  PetscCall(DMSetApplicationContext(dm, &ctx));
  PetscCall(SetupDiscretization(dm, &ctx));

  PetscCall(TSCreate(PETSC_COMM_WORLD, &ts));
  PetscCall(TSSetDM(ts, dm));
  PetscCall(DMTSSetBoundaryLocal(dm, DMPlexTSComputeBoundary, &ctx));
  if (ctx.expTS) {
    PetscCall(DMTSSetRHSFunctionLocal(dm, DMPlexTSComputeRHSFunctionFEM, &ctx));
    if (ctx.lumped) PetscCall(DMTSCreateRHSMassMatrixLumped(dm));
    else PetscCall(DMTSCreateRHSMassMatrix(dm));
  } else {
    PetscCall(DMTSSetIFunctionLocal(dm, DMPlexTSComputeIFunctionFEM, &ctx));
    PetscCall(DMTSSetIJacobianLocal(dm, DMPlexTSComputeIJacobianFEM, &ctx));
  }
  PetscCall(TSSetMaxTime(ts, 1.0));
  PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_MATCHSTEP));
  PetscCall(TSSetFromOptions(ts));
  PetscCall(TSSetComputeInitialCondition(ts, SetInitialConditions));
  PetscCall(TSSetResize(ts, PETSC_FALSE, TransferSetUp, TransferVecs, &ctx));

  PetscCall(DMCreateGlobalVector(dm, &u));
  PetscCall(DMTSCheckFromOptions(ts, u));
  PetscCall(SetInitialConditions(ts, u));
  PetscCall(PetscObjectSetName((PetscObject)u, "temperature"));

  PetscCall(TSSetSolution(ts, u));
  PetscCall(VecViewFromOptions(u, NULL, "-u0_view"));
  PetscCall(VecDestroy(&u));
  PetscCall(TSSolve(ts, NULL));

  PetscCall(TSGetSolution(ts, &u));
  PetscCall(VecViewFromOptions(u, NULL, "-uf_view"));
  PetscCall(DMTSCheckFromOptions(ts, u));
  if (ctx.expTS) PetscCall(DMTSDestroyRHSMassMatrix(dm));

  PetscCall(TSDestroy(&ts));
  PetscCall(DMDestroy(&dm));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

  test:
    suffix: 2d_p1
    requires: triangle
    args: -sol_type quadratic_linear -dm_refine 1 -temp_petscspace_degree 1 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 2d_p1_exp
    requires: triangle
    args: -sol_type quadratic_linear -dm_refine 1 -temp_petscspace_degree 1 -explicit \
          -ts_type euler -ts_max_steps 4 -ts_time_step 1e-3 -ts_monitor_error
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [1.9]
    suffix: 2d_p1_sconv
    requires: triangle
    args: -sol_type quadratic_linear -temp_petscspace_degree 1 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [2.1]
    suffix: 2d_p1_sconv_2
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 1 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 1e-6 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 4 -convest_num_refine 3 get L_2 convergence rate: [1.2]
    suffix: 2d_p1_tconv
    requires: triangle
    args: -sol_type quadratic_trig -temp_petscspace_degree 1 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 6 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 2d_p1_tconv_2
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 1 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # The L_2 convergence rate cannot be seen since stability of the explicit integrator requires that is be more accurate than the grid
    suffix: 2d_p1_exp_tconv_2
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 1 -explicit -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type euler -ts_max_steps 4 -ts_time_step 1e-4 -lumped 0 -mass_pc_type lu
  test:
    # The L_2 convergence rate cannot be seen since stability of the explicit integrator requires that is be more accurate than the grid
    suffix: 2d_p1_exp_tconv_2_lump
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 1 -explicit -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type euler -ts_max_steps 4 -ts_time_step 1e-4
  test:
    suffix: 2d_p2
    requires: triangle
    args: -sol_type quadratic_linear -dm_refine 0 -temp_petscspace_degree 2 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [2.9]
    suffix: 2d_p2_sconv
    requires: triangle
    args: -sol_type trig_linear -temp_petscspace_degree 2 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00000001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [3.1]
    suffix: 2d_p2_sconv_2
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 2 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00000001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 3 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 2d_p2_tconv
    requires: triangle
    args: -sol_type quadratic_trig -temp_petscspace_degree 2 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 3 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 2d_p2_tconv_2
    requires: triangle
    args: -sol_type trig_trig -temp_petscspace_degree 2 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 2d_q1
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -dm_refine 1 -temp_petscspace_degree 1 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [1.9]
    suffix: 2d_q1_sconv
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -temp_petscspace_degree 1 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 4 -convest_num_refine 3 get L_2 convergence rate: [1.2]
    suffix: 2d_q1_tconv
    args: -sol_type quadratic_trig -dm_plex_simplex 0 -temp_petscspace_degree 1 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 2d_q2
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -dm_refine 0 -temp_petscspace_degree 2 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [2.9]
    suffix: 2d_q2_sconv
    args: -sol_type trig_linear -dm_plex_simplex 0 -temp_petscspace_degree 2 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00000001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 3 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 2d_q2_tconv
    args: -sol_type quadratic_trig -dm_plex_simplex 0 -temp_petscspace_degree 2 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu

  test:
    suffix: 3d_p1
    requires: ctetgen
    args: -sol_type quadratic_linear -dm_refine 1 -temp_petscspace_degree 1 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [1.9]
    suffix: 3d_p1_sconv
    requires: ctetgen
    args: -sol_type quadratic_linear -temp_petscspace_degree 1 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 4 -convest_num_refine 3 get L_2 convergence rate: [1.2]
    suffix: 3d_p1_tconv
    requires: ctetgen
    args: -sol_type quadratic_trig -temp_petscspace_degree 1 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 3d_p2
    requires: ctetgen
    args: -sol_type quadratic_linear -dm_refine 0 -temp_petscspace_degree 2 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [2.9]
    suffix: 3d_p2_sconv
    requires: ctetgen
    args: -sol_type trig_linear -temp_petscspace_degree 2 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00000001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 3 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 3d_p2_tconv
    requires: ctetgen
    args: -sol_type quadratic_trig -temp_petscspace_degree 2 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 3d_q1
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -dm_refine 1 -temp_petscspace_degree 1 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [1.9]
    suffix: 3d_q1_sconv
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -temp_petscspace_degree 1 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 4 -convest_num_refine 3 get L_2 convergence rate: [1.2]
    suffix: 3d_q1_tconv
    args: -sol_type quadratic_trig -dm_plex_simplex 0 -temp_petscspace_degree 1 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    suffix: 3d_q2
    args: -sol_type quadratic_linear -dm_plex_simplex 0 -dm_refine 0 -temp_petscspace_degree 2 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 2 -convest_num_refine 3 get L_2 convergence rate: [2.9]
    suffix: 3d_q2_sconv
    args: -sol_type trig_linear -dm_plex_simplex 0 -temp_petscspace_degree 2 -ts_convergence_estimate -ts_convergence_temporal 0 -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 1 -ts_time_step 0.00000001 -snes_error_if_not_converged -pc_type lu
  test:
    # -dm_refine 3 -convest_num_refine 3 get L_2 convergence rate: [1.0]
    suffix: 3d_q2_tconv
    args: -sol_type quadratic_trig -dm_plex_simplex 0 -temp_petscspace_degree 2 -ts_convergence_estimate -convest_num_refine 1 \
          -ts_type beuler -ts_max_steps 4 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu

  test:
    # For a nice picture, -bd_dm_refine 2 -dm_refine 1 -dm_view hdf5:${PETSC_DIR}/sol.h5 -ts_monitor_solution hdf5:${PETSC_DIR}/sol.h5::append
    suffix: egads_sphere
    requires: egads ctetgen datafilespath
    args: -sol_type quadratic_linear \
          -dm_plex_boundary_filename ${DATAFILESPATH}/meshes/cad/sphere_example.egadslite -dm_plex_boundary_label marker \
          -temp_petscspace_degree 2 -dmts_check .0001 \
          -ts_type beuler -ts_max_steps 5 -ts_time_step 0.1 -snes_error_if_not_converged -pc_type lu

  test:
    suffix: remesh
    requires: triangle mmg
    args: -sol_type quadratic_trig -dm_refine 2 -temp_petscspace_degree 1 -ts_type beuler -ts_time_step 0.01 -snes_error_if_not_converged -pc_type lu -grad_petscspace_degree 1 -dm_adaptor mmg -dm_plex_hash_location -remesh_every 5
    output_file: output/empty.out

TEST*/