static char help[] = "Basic equation for generator stability analysis.\n";

/*F

\begin{eqnarray}
                 \frac{d \theta}{dt} = \omega_b (\omega - \omega_s)
                 \frac{2 H}{\omega_s}\frac{d \omega}{dt} & = & P_m - P_max \sin(\theta) -D(\omega - \omega_s)\\
\end{eqnarray}

  Ensemble of initial conditions
   ./ex9 -ensemble -ts_monitor_draw_solution_phase -1,-3,3,3 -ts_adapt_dt_max .01 -ts_monitor -ts_type rk -pc_type lu -ksp_type preonly

  Fault at .1 seconds
   ./ex9 -ts_monitor_draw_solution_phase .42,.95,.6,1.05 -ts_adapt_dt_max .01 -ts_monitor -ts_type rk -pc_type lu -ksp_type preonly

  Initial conditions same as when fault is ended
   ./ex9 -u 0.496792,1.00932 -ts_monitor_draw_solution_phase .42,.95,.6,1.05 -ts_adapt_dt_max .01 -ts_monitor -ts_type rk -pc_type lu -ksp_type preonly

F*/

/*
   Include "petscts.h" so that we can use TS solvers.  Note that this
   file automatically includes:
     petscsys.h       - base PETSc routines   petscvec.h - vectors
     petscmat.h - matrices
     petscis.h     - index sets            petscksp.h - Krylov subspace methods
     petscviewer.h - viewers               petscpc.h  - preconditioners
     petscksp.h   - linear solvers
*/

#include <petscts.h>

typedef struct {
  PetscScalar H, D, omega_b, omega_s, Pmax, Pm, E, V, X, u_s, c;
  PetscInt    beta;
  PetscReal   tf, tcl;
} AppCtx;

PetscErrorCode PostStepFunction(TS ts)
{
  Vec                U;
  PetscReal          t;
  const PetscScalar *u;

  PetscFunctionBegin;
  PetscCall(TSGetTime(ts, &t));
  PetscCall(TSGetSolution(ts, &U));
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(PetscPrintf(PETSC_COMM_SELF, "delta(%3.2f) = %8.7f\n", (double)t, (double)u[0]));
  PetscCall(VecRestoreArrayRead(U, &u));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
     Defines the ODE passed to the ODE solver
*/
static PetscErrorCode RHSFunction(TS ts, PetscReal t, Vec U, Vec F, AppCtx *ctx)
{
  PetscScalar       *f, Pmax;
  const PetscScalar *u;

  PetscFunctionBegin;
  /*  The next three lines allow us to access the entries of the vectors directly */
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(VecGetArray(F, &f));
  if ((t > ctx->tf) && (t < ctx->tcl)) Pmax = 0.0; /* A short-circuit on the generator terminal that drives the electrical power output (Pmax*sin(delta)) to 0 */
  else Pmax = ctx->Pmax;

  f[0] = ctx->omega_b * (u[1] - ctx->omega_s);
  f[1] = (-Pmax * PetscSinScalar(u[0]) - ctx->D * (u[1] - ctx->omega_s) + ctx->Pm) * ctx->omega_s / (2.0 * ctx->H);

  PetscCall(VecRestoreArrayRead(U, &u));
  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 RHSJacobian(TS ts, PetscReal t, Vec U, Mat A, Mat B, AppCtx *ctx)
{
  PetscInt           rowcol[] = {0, 1};
  PetscScalar        J[2][2], Pmax;
  const PetscScalar *u;

  PetscFunctionBegin;
  PetscCall(VecGetArrayRead(U, &u));
  if ((t > ctx->tf) && (t < ctx->tcl)) Pmax = 0.0; /* A short-circuit on the generator terminal that drives the electrical power output (Pmax*sin(delta)) to 0 */
  else Pmax = ctx->Pmax;

  J[0][0] = 0;
  J[0][1] = ctx->omega_b;
  J[1][1] = -ctx->D * ctx->omega_s / (2.0 * ctx->H);
  J[1][0] = -Pmax * PetscCosScalar(u[0]) * ctx->omega_s / (2.0 * ctx->H);

  PetscCall(MatSetValues(A, 2, rowcol, 2, rowcol, &J[0][0], INSERT_VALUES));
  PetscCall(VecRestoreArrayRead(U, &u));

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

static PetscErrorCode RHSJacobianP(TS ts, PetscReal t, Vec X, Mat A, PetscCtx ctx0)
{
  PetscInt    row[] = {0, 1}, col[] = {0};
  PetscScalar J[2][1];
  AppCtx     *ctx = (AppCtx *)ctx0;

  PetscFunctionBeginUser;
  J[0][0] = 0;
  J[1][0] = ctx->omega_s / (2.0 * ctx->H);
  PetscCall(MatSetValues(A, 2, row, 1, col, &J[0][0], INSERT_VALUES));
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode CostIntegrand(TS ts, PetscReal t, Vec U, Vec R, AppCtx *ctx)
{
  PetscScalar       *r;
  const PetscScalar *u;

  PetscFunctionBegin;
  PetscCall(VecGetArrayRead(U, &u));
  PetscCall(VecGetArray(R, &r));
  r[0] = ctx->c * PetscPowScalarInt(PetscMax(0., u[0] - ctx->u_s), ctx->beta);
  PetscCall(VecRestoreArray(R, &r));
  PetscCall(VecRestoreArrayRead(U, &u));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode DRDUJacobianTranspose(TS ts, PetscReal t, Vec U, Mat DRDU, Mat B, AppCtx *ctx)
{
  PetscScalar        ru[1];
  const PetscScalar *u;
  PetscInt           row[] = {0}, col[] = {0};

  PetscFunctionBegin;
  PetscCall(VecGetArrayRead(U, &u));
  ru[0] = ctx->c * ctx->beta * PetscPowScalarInt(PetscMax(0., u[0] - ctx->u_s), ctx->beta - 1);
  PetscCall(VecRestoreArrayRead(U, &u));
  PetscCall(MatSetValues(DRDU, 1, row, 1, col, ru, INSERT_VALUES));
  PetscCall(MatAssemblyBegin(DRDU, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(DRDU, MAT_FINAL_ASSEMBLY));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode DRDPJacobianTranspose(TS ts, PetscReal t, Vec U, Mat DRDP, AppCtx *ctx)
{
  PetscFunctionBegin;
  PetscCall(MatZeroEntries(DRDP));
  PetscCall(MatAssemblyBegin(DRDP, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(DRDP, MAT_FINAL_ASSEMBLY));
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode ComputeSensiP(Vec lambda, Vec mu, AppCtx *ctx)
{
  PetscScalar        sensip;
  const PetscScalar *x, *y;

  PetscFunctionBegin;
  PetscCall(VecGetArrayRead(lambda, &x));
  PetscCall(VecGetArrayRead(mu, &y));
  sensip = 1. / PetscSqrtScalar(1. - (ctx->Pm / ctx->Pmax) * (ctx->Pm / ctx->Pmax)) / ctx->Pmax * x[0] + y[0];
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\n sensitivity wrt parameter pm: %.7f \n", (double)sensip));
  PetscCall(VecRestoreArrayRead(lambda, &x));
  PetscCall(VecRestoreArrayRead(mu, &y));
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **argv)
{
  TS           ts, quadts; /* ODE integrator */
  Vec          U;          /* solution will be stored here */
  Mat          A;          /* Jacobian matrix */
  Mat          Jacp;       /* Jacobian matrix */
  Mat          DRDU, DRDP;
  PetscMPIInt  size;
  PetscInt     n = 2;
  AppCtx       ctx;
  PetscScalar *u;
  PetscReal    du[2]    = {0.0, 0.0};
  PetscBool    ensemble = PETSC_FALSE, flg1, flg2;
  PetscReal    ftime;
  PetscInt     steps;
  PetscScalar *x_ptr, *y_ptr;
  Vec          lambda[1], q, mu[1];

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Initialize program
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "Only for sequential runs");

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Create necessary matrix and vectors
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatSetSizes(A, n, n, PETSC_DETERMINE, PETSC_DETERMINE));
  PetscCall(MatSetType(A, MATDENSE));
  PetscCall(MatSetFromOptions(A));
  PetscCall(MatSetUp(A));

  PetscCall(MatCreateVecs(A, &U, NULL));

  PetscCall(MatCreate(PETSC_COMM_WORLD, &Jacp));
  PetscCall(MatSetSizes(Jacp, PETSC_DECIDE, PETSC_DECIDE, 2, 1));
  PetscCall(MatSetFromOptions(Jacp));
  PetscCall(MatSetUp(Jacp));

  PetscCall(MatCreateDense(PETSC_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE, 1, 1, NULL, &DRDP));
  PetscCall(MatSetUp(DRDP));
  PetscCall(MatCreateDense(PETSC_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE, 1, 2, NULL, &DRDU));
  PetscCall(MatSetUp(DRDU));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Set runtime options
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscOptionsBegin(PETSC_COMM_WORLD, NULL, "Swing equation options", "");
  {
    ctx.beta    = 2;
    ctx.c       = 10000.0;
    ctx.u_s     = 1.0;
    ctx.omega_s = 1.0;
    ctx.omega_b = 120.0 * PETSC_PI;
    ctx.H       = 5.0;
    PetscCall(PetscOptionsScalar("-Inertia", "", "", ctx.H, &ctx.H, NULL));
    ctx.D = 5.0;
    PetscCall(PetscOptionsScalar("-D", "", "", ctx.D, &ctx.D, NULL));
    ctx.E    = 1.1378;
    ctx.V    = 1.0;
    ctx.X    = 0.545;
    ctx.Pmax = ctx.E * ctx.V / ctx.X;
    PetscCall(PetscOptionsScalar("-Pmax", "", "", ctx.Pmax, &ctx.Pmax, NULL));
    ctx.Pm = 1.1;
    PetscCall(PetscOptionsScalar("-Pm", "", "", ctx.Pm, &ctx.Pm, NULL));
    ctx.tf  = 0.1;
    ctx.tcl = 0.2;
    PetscCall(PetscOptionsReal("-tf", "Time to start fault", "", ctx.tf, &ctx.tf, NULL));
    PetscCall(PetscOptionsReal("-tcl", "Time to end fault", "", ctx.tcl, &ctx.tcl, NULL));
    PetscCall(PetscOptionsBool("-ensemble", "Run ensemble of different initial conditions", "", ensemble, &ensemble, NULL));
    if (ensemble) {
      ctx.tf  = -1;
      ctx.tcl = -1;
    }

    PetscCall(VecGetArray(U, &u));
    u[0] = PetscAsinScalar(ctx.Pm / ctx.Pmax);
    u[1] = 1.0;
    PetscCall(PetscOptionsRealArray("-u", "Initial solution", "", u, &n, &flg1));
    n = 2;
    PetscCall(PetscOptionsRealArray("-du", "Perturbation in initial solution", "", du, &n, &flg2));
    u[0] += du[0];
    u[1] += du[1];
    PetscCall(VecRestoreArray(U, &u));
    if (flg1 || flg2) {
      ctx.tf  = -1;
      ctx.tcl = -1;
    }
  }
  PetscOptionsEnd();

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Create timestepping solver context
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSCreate(PETSC_COMM_WORLD, &ts));
  PetscCall(TSSetProblemType(ts, TS_NONLINEAR));
  PetscCall(TSSetEquationType(ts, TS_EQ_ODE_EXPLICIT)); /* less Jacobian evaluations when adjoint BEuler is used, otherwise no effect */
  PetscCall(TSSetType(ts, TSRK));
  PetscCall(TSSetRHSFunction(ts, NULL, (TSRHSFunctionFn *)RHSFunction, &ctx));
  PetscCall(TSSetRHSJacobian(ts, A, A, (TSRHSJacobianFn *)RHSJacobian, &ctx));
  PetscCall(TSCreateQuadratureTS(ts, PETSC_TRUE, &quadts));
  PetscCall(TSSetRHSFunction(quadts, NULL, (TSRHSFunctionFn *)CostIntegrand, &ctx));
  PetscCall(TSSetRHSJacobian(quadts, DRDU, DRDU, (TSRHSJacobianFn *)DRDUJacobianTranspose, &ctx));
  PetscCall(TSSetRHSJacobianP(quadts, DRDP, (TSRHSJacobianPFn *)DRDPJacobianTranspose, &ctx));
  PetscCall(TSSetCostGradients(ts, 1, lambda, mu));
  PetscCall(TSSetRHSJacobianP(ts, Jacp, RHSJacobianP, &ctx));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set initial conditions
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetSolution(ts, U));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Save trajectory of solution so that TSAdjointSolve() may be used
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetSaveTrajectory(ts));

  PetscCall(MatCreateVecs(A, &lambda[0], NULL));
  /*   Set initial conditions for the adjoint integration */
  PetscCall(VecGetArray(lambda[0], &y_ptr));
  y_ptr[0] = 0.0;
  y_ptr[1] = 0.0;
  PetscCall(VecRestoreArray(lambda[0], &y_ptr));

  PetscCall(MatCreateVecs(Jacp, &mu[0], NULL));
  PetscCall(VecGetArray(mu[0], &x_ptr));
  x_ptr[0] = -1.0;
  PetscCall(VecRestoreArray(mu[0], &x_ptr));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Set solver options
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(TSSetMaxTime(ts, 10.0));
  PetscCall(TSSetExactFinalTime(ts, TS_EXACTFINALTIME_MATCHSTEP));
  PetscCall(TSSetTimeStep(ts, .01));
  PetscCall(TSSetFromOptions(ts));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Solve nonlinear system
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  if (ensemble) {
    for (du[1] = -2.5; du[1] <= .01; du[1] += .1) {
      PetscCall(VecGetArray(U, &u));
      u[0] = PetscAsinScalar(ctx.Pm / ctx.Pmax);
      u[1] = ctx.omega_s;
      u[0] += du[0];
      u[1] += du[1];
      PetscCall(VecRestoreArray(U, &u));
      PetscCall(TSSetTimeStep(ts, .01));
      PetscCall(TSSolve(ts, U));
    }
  } else {
    PetscCall(TSSolve(ts, U));
  }
  PetscCall(VecView(U, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(TSGetSolveTime(ts, &ftime));
  PetscCall(TSGetStepNumber(ts, &steps));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Adjoint model starts here
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  /*   Set initial conditions for the adjoint integration */
  PetscCall(VecGetArray(lambda[0], &y_ptr));
  y_ptr[0] = 0.0;
  y_ptr[1] = 0.0;
  PetscCall(VecRestoreArray(lambda[0], &y_ptr));

  PetscCall(VecGetArray(mu[0], &x_ptr));
  x_ptr[0] = -1.0;
  PetscCall(VecRestoreArray(mu[0], &x_ptr));

  PetscCall(TSAdjointSolve(ts));

  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\n sensitivity wrt initial conditions: d[Psi(tf)]/d[phi0]  d[Psi(tf)]/d[omega0]\n"));
  PetscCall(VecView(lambda[0], PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(VecView(mu[0], PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(TSGetCostIntegral(ts, &q));
  PetscCall(VecView(q, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(VecGetArray(q, &x_ptr));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\n cost function=%g\n", (double)(x_ptr[0] - ctx.Pm)));
  PetscCall(VecRestoreArray(q, &x_ptr));

  PetscCall(ComputeSensiP(lambda[0], mu[0], &ctx));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Free work space.  All PETSc objects should be destroyed when they are no longer needed.
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  PetscCall(MatDestroy(&A));
  PetscCall(MatDestroy(&Jacp));
  PetscCall(MatDestroy(&DRDU));
  PetscCall(MatDestroy(&DRDP));
  PetscCall(VecDestroy(&U));
  PetscCall(VecDestroy(&lambda[0]));
  PetscCall(VecDestroy(&mu[0]));
  PetscCall(TSDestroy(&ts));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   build:
      requires: !complex

   test:
      args: -viewer_binary_skip_info -ts_adapt_type none

TEST*/