#include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h> /*I  "petscksp.h"  I*/

PetscErrorCode KSPSetFromOptions_BCGS(KSP ksp, PetscOptionItems PetscOptionsObject)
{
  PetscFunctionBegin;
  PetscOptionsHeadBegin(PetscOptionsObject, "KSP BCGS Options");
  PetscOptionsHeadEnd();
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode KSPSetUp_BCGS(KSP ksp)
{
  PetscFunctionBegin;
  PetscCall(KSPSetWorkVecs(ksp, 6));
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode KSPSolve_BCGS(KSP ksp)
{
  PetscInt    i;
  PetscScalar rho, rhoold, alpha, beta, omega, omegaold, d1;
  Vec         X, B, V, P, R, RP, T, S;
  PetscReal   dp   = 0.0, d2;
  KSP_BCGS   *bcgs = (KSP_BCGS *)ksp->data;

  PetscFunctionBegin;
  X  = ksp->vec_sol;
  B  = ksp->vec_rhs;
  R  = ksp->work[0];
  RP = ksp->work[1];
  V  = ksp->work[2];
  T  = ksp->work[3];
  S  = ksp->work[4];
  P  = ksp->work[5];

  /* Compute initial preconditioned residual */
  PetscCall(KSPInitialResidual(ksp, X, V, T, R, B));

  /* with right preconditioning need to save initial guess to add to final solution */
  if (ksp->pc_side == PC_RIGHT && !ksp->guess_zero) {
    if (!bcgs->guess) PetscCall(VecDuplicate(X, &bcgs->guess));
    PetscCall(VecCopy(X, bcgs->guess));
    PetscCall(VecSet(X, 0.0));
  }

  /* Test for nothing to do */
  if (ksp->normtype != KSP_NORM_NONE) {
    PetscCall(VecNorm(R, NORM_2, &dp));
    KSPCheckNorm(ksp, dp);
  }
  PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
  ksp->its   = 0;
  ksp->rnorm = dp;
  PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
  PetscCall(KSPLogResidualHistory(ksp, dp));
  PetscCall(KSPMonitor(ksp, 0, dp));
  PetscCall((*ksp->converged)(ksp, 0, dp, &ksp->reason, ksp->cnvP));
  if (ksp->reason) {
    if (bcgs->guess) PetscCall(VecAXPY(X, 1.0, bcgs->guess));
    PetscFunctionReturn(PETSC_SUCCESS);
  }

  /* Make the initial Rp == R */
  PetscCall(VecCopy(R, RP));

  rhoold   = 1.0;
  alpha    = 1.0;
  omegaold = 1.0;
  PetscCall(VecSet(P, 0.0));
  PetscCall(VecSet(V, 0.0));

  i = 0;
  do {
    PetscCall(VecDot(R, RP, &rho)); /*   rho <- (r,rp)      */
    beta = (rho / rhoold) * (alpha / omegaold);
    PetscCall(VecAXPBYPCZ(P, 1.0, -omegaold * beta, beta, R, V)); /* p <- r - omega * beta* v + beta * p */
    PetscCall(KSP_PCApplyBAorAB(ksp, P, V, T));                   /*   v <- K p           */
    PetscCall(VecDot(V, RP, &d1));
    KSPCheckDot(ksp, d1);
    if (d1 == 0.0) {
      PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve breakdown due to zero inner product");
      ksp->reason = KSP_DIVERGED_BREAKDOWN;
      PetscCall(PetscInfo(ksp, "Breakdown due to zero inner product\n"));
      break;
    }
    alpha = rho / d1;                           /*   a <- rho / (v,rp)  */
    PetscCall(VecWAXPY(S, -alpha, V, R));       /*   s <- r - a v       */
    PetscCall(KSP_PCApplyBAorAB(ksp, S, T, R)); /*   t <- K s    */
    PetscCall(VecDotNorm2(S, T, &d1, &d2));
    if (d2 == 0.0) {
      /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
         may be our solution.  Give it a try? */
      PetscCall(VecDot(S, S, &d1));
      if (d1 != 0.0) {
        PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve has failed due to singular preconditioned operator");
        ksp->reason = KSP_DIVERGED_BREAKDOWN;
        PetscCall(PetscInfo(ksp, "Failed due to singular preconditioned operator\n"));
        break;
      }
      PetscCall(VecAXPY(X, alpha, P)); /*   x <- x + a p       */
      PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
      ksp->its++;
      ksp->rnorm  = 0.0;
      ksp->reason = KSP_CONVERGED_RTOL;
      PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
      PetscCall(KSPLogResidualHistory(ksp, dp));
      PetscCall(KSPMonitor(ksp, i + 1, 0.0));
      break;
    }
    omega = d1 / d2;                                    /*   w <- (t's) / (t't) */
    PetscCall(VecAXPBYPCZ(X, alpha, omega, 1.0, P, S)); /* x <- alpha * p + omega * s + x */
    PetscCall(VecWAXPY(R, -omega, T, S));               /*   r <- s - w t       */
    if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i + 2) {
      PetscCall(VecNorm(R, NORM_2, &dp));
      KSPCheckNorm(ksp, dp);
    }

    rhoold   = rho;
    omegaold = omega;

    PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
    ksp->its++;
    ksp->rnorm = dp;
    PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
    PetscCall(KSPLogResidualHistory(ksp, dp));
    PetscCall(KSPMonitor(ksp, i + 1, dp));
    PetscCall((*ksp->converged)(ksp, i + 1, dp, &ksp->reason, ksp->cnvP));
    if (ksp->reason) break;
    if (rho == 0.0) {
      PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve breakdown due to zero inner product");
      ksp->reason = KSP_DIVERGED_BREAKDOWN;
      PetscCall(PetscInfo(ksp, "Breakdown due to zero rho inner product\n"));
      break;
    }
    i++;
  } while (i < ksp->max_it);

  if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

  PetscCall(KSPUnwindPreconditioner(ksp, X, T));
  if (bcgs->guess) PetscCall(VecAXPY(X, 1.0, bcgs->guess));
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode KSPBuildSolution_BCGS(KSP ksp, Vec v, Vec *V)
{
  KSP_BCGS *bcgs = (KSP_BCGS *)ksp->data;

  PetscFunctionBegin;
  if (ksp->pc_side == PC_RIGHT) {
    PetscCheck(v, PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Not working with right preconditioner");
    PetscCall(KSP_PCApply(ksp, ksp->vec_sol, v));
    if (bcgs->guess) PetscCall(VecAXPY(v, 1.0, bcgs->guess));
    *V = v;
  } else {
    if (v) {
      PetscCall(VecCopy(ksp->vec_sol, v));
      *V = v;
    } else *V = ksp->vec_sol;
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode KSPReset_BCGS(KSP ksp)
{
  KSP_BCGS *cg = (KSP_BCGS *)ksp->data;

  PetscFunctionBegin;
  PetscCall(VecDestroy(&cg->guess));
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode KSPDestroy_BCGS(KSP ksp)
{
  PetscFunctionBegin;
  PetscCall(KSPReset_BCGS(ksp));
  PetscCall(KSPDestroyDefault(ksp));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*MC
   KSPBCGS - Implements the BiCGStab (Stabilized version of Biconjugate Gradient) method {cite}`vorst92`

   Level: beginner

   Notes:
   Supports left and right preconditioning but not symmetric

   See `KSPBCGSL` for additional stabilization

   See `KSPFBCGS`, `KSPFBCGSR`, and `KSPPIPEBCGS` for flexible and pipelined versions of the algorithm

   This method can be a good alternative to `KSPGMRES` in that it does not require explicitly storing the Krylov space as `KSPGMRES` requires
   and there is no acceptable restart value that can be set with `KSPGMRESSetRestart()` that balances cost per iteration and convergence rates with `KSPGMRES`.

.seealso: [](ch_ksp), `KSPFBCGS`, `KSPFBCGSR`, `KSPPIPEBCGS`, `KSPBCGSL`, `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPFBICG`, `KSPQMRCGS`, `KSPSetPCSide()`
M*/
PETSC_EXTERN PetscErrorCode KSPCreate_BCGS(KSP ksp)
{
  KSP_BCGS *bcgs;

  PetscFunctionBegin;
  PetscCall(PetscNew(&bcgs));

  ksp->data                = bcgs;
  ksp->ops->setup          = KSPSetUp_BCGS;
  ksp->ops->solve          = KSPSolve_BCGS;
  ksp->ops->destroy        = KSPDestroy_BCGS;
  ksp->ops->reset          = KSPReset_BCGS;
  ksp->ops->buildsolution  = KSPBuildSolution_BCGS;
  ksp->ops->buildresidual  = KSPBuildResidualDefault;
  ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;

  PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3));
  PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2));
  PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1));
  PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1));
  PetscFunctionReturn(PETSC_SUCCESS);
}
