/*
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   SLEPc - Scalable Library for Eigenvalue Problem Computations
   Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain

   This file is part of SLEPc.
   SLEPc is distributed under a 2-clause BSD license (see LICENSE).
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
/*
   BV operations involving global communication
*/

#include <slepc/private/bvimpl.h>      /*I "slepcbv.h" I*/

/*
  BVDot for the particular case of non-standard inner product with
  matrix B, which is assumed to be symmetric (or complex Hermitian)
*/
static inline PetscErrorCode BVDot_Private(BV X,BV Y,Mat M)
{
  PetscObjectId  idx,idy;
  PetscInt       i,j,jend,m;
  PetscScalar    *marray;
  PetscBool      symm=PETSC_FALSE;
  Mat            B;
  Vec            z;

  PetscFunctionBegin;
  BVCheckOp(Y,1,dotvec);
  PetscCall(MatGetSize(M,&m,NULL));
  PetscCall(MatDenseGetArray(M,&marray));
  PetscCall(PetscObjectGetId((PetscObject)X,&idx));
  PetscCall(PetscObjectGetId((PetscObject)Y,&idy));
  B = Y->matrix;
  Y->matrix = NULL;
  if (idx==idy) symm=PETSC_TRUE;  /* M=X'BX is symmetric */
  jend = X->k;
  for (j=X->l;j<jend;j++) {
    if (symm) Y->k = j+1;
    PetscCall(BVGetColumn(X->cached,j,&z));
    PetscCall((*Y->ops->dotvec)(Y,z,marray+j*m+Y->l));
    PetscCall(BVRestoreColumn(X->cached,j,&z));
    if (symm) {
      for (i=X->l;i<j;i++)
        marray[j+i*m] = PetscConj(marray[i+j*m]);
    }
  }
  PetscCall(MatDenseRestoreArray(M,&marray));
  Y->matrix = B;
  PetscFunctionReturn(0);
}

/*@
   BVDot - Computes the 'block-dot' product of two basis vectors objects.

   Collective on X

   Input Parameters:
+  X - first basis vectors
-  Y - second basis vectors

   Output Parameter:
.  M - the resulting matrix

   Notes:
   This is the generalization of VecDot() for a collection of vectors, M = Y^H*X.
   The result is a matrix M whose entry m_ij is equal to y_i^H x_j (where y_i^H
   denotes the conjugate transpose of y_i).

   If a non-standard inner product has been specified with BVSetMatrix(),
   then the result is M = Y^H*B*X. In this case, both X and Y must have
   the same associated matrix.

   On entry, M must be a sequential dense Mat with dimensions m,n at least, where
   m is the number of active columns of Y and n is the number of active columns of X.
   Only rows (resp. columns) of M starting from ly (resp. lx) are computed,
   where ly (resp. lx) is the number of leading columns of Y (resp. X).

   X and Y need not be different objects.

   Level: intermediate

.seealso: BVDotVec(), BVDotColumn(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVDot(BV X,BV Y,Mat M)
{
  PetscInt       m,n;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidHeaderSpecific(Y,BV_CLASSID,2);
  PetscValidHeaderSpecific(M,MAT_CLASSID,3);
  PetscValidType(X,1);
  BVCheckSizes(X,1);
  PetscValidType(Y,2);
  BVCheckSizes(Y,2);
  PetscValidType(M,3);
  PetscCheckSameTypeAndComm(X,1,Y,2);
  PetscCheckTypeNames(M,MATSEQDENSE,MATSEQDENSECUDA);

  PetscCall(MatGetSize(M,&m,&n));
  PetscCheck(m>=Y->k,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_SIZ,"Mat argument has %" PetscInt_FMT " rows, should have at least %" PetscInt_FMT,m,Y->k);
  PetscCheck(n>=X->k,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_SIZ,"Mat argument has %" PetscInt_FMT " columns, should have at least %" PetscInt_FMT,n,X->k);
  PetscCheck(X->n==Y->n,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension X %" PetscInt_FMT ", Y %" PetscInt_FMT,X->n,Y->n);
  PetscCheck(X->matrix==Y->matrix,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"X and Y must have the same inner product matrix");
  if (X->l==X->k || Y->l==Y->k) PetscFunctionReturn(0);

  PetscCall(PetscLogEventBegin(BV_Dot,X,Y,0,0));
  if (X->matrix) { /* non-standard inner product */
    /* compute BX first */
    PetscCall(BV_IPMatMultBV(X));
    if (X->vmm==BV_MATMULT_VECS) {
      /* perform computation column by column */
      PetscCall(BVDot_Private(X,Y,M));
    } else PetscCall((*X->ops->dot)(X->cached,Y,M));
  } else PetscCall((*X->ops->dot)(X,Y,M));
  PetscCall(PetscLogEventEnd(BV_Dot,X,Y,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVDotVec - Computes multiple dot products of a vector against all the
   column vectors of a BV.

   Collective on X

   Input Parameters:
+  X - basis vectors
-  y - a vector

   Output Parameter:
.  m - an array where the result must be placed

   Notes:
   This is analogue to VecMDot(), but using BV to represent a collection
   of vectors. The result is m = X^H*y, so m_i is equal to x_j^H y. Note
   that here X is transposed as opposed to BVDot().

   If a non-standard inner product has been specified with BVSetMatrix(),
   then the result is m = X^H*B*y.

   The length of array m must be equal to the number of active columns of X
   minus the number of leading columns, i.e. the first entry of m is the
   product of the first non-leading column with y.

   Level: intermediate

.seealso: BVDot(), BVDotColumn(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVDotVec(BV X,Vec y,PetscScalar m[])
{
  PetscInt       n;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidHeaderSpecific(y,VEC_CLASSID,2);
  PetscValidType(X,1);
  BVCheckSizes(X,1);
  BVCheckOp(X,1,dotvec);
  PetscValidType(y,2);
  PetscCheckSameTypeAndComm(X,1,y,2);

  PetscCall(VecGetLocalSize(y,&n));
  PetscCheck(X->n==n,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension X %" PetscInt_FMT ", y %" PetscInt_FMT,X->n,n);

  PetscCall(PetscLogEventBegin(BV_DotVec,X,y,0,0));
  PetscCall((*X->ops->dotvec)(X,y,m));
  PetscCall(PetscLogEventEnd(BV_DotVec,X,y,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVDotVecBegin - Starts a split phase dot product computation.

   Input Parameters:
+  X - basis vectors
.  y - a vector
-  m - an array where the result will go (can be NULL)

   Note:
   Each call to BVDotVecBegin() should be paired with a call to BVDotVecEnd().

   Level: advanced

.seealso: BVDotVecEnd(), BVDotVec()
@*/
PetscErrorCode BVDotVecBegin(BV X,Vec y,PetscScalar *m)
{
  PetscInt            i,n,nv;
  PetscSplitReduction *sr;
  MPI_Comm            comm;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidHeaderSpecific(y,VEC_CLASSID,2);
  PetscValidType(X,1);
  BVCheckSizes(X,1);
  PetscValidType(y,2);
  PetscCheckSameTypeAndComm(X,1,y,2);

  PetscCall(VecGetLocalSize(y,&n));
  PetscCheck(X->n==n,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension X %" PetscInt_FMT ", y %" PetscInt_FMT,X->n,n);

  if (X->ops->dotvec_begin) PetscCall((*X->ops->dotvec_begin)(X,y,m));
  else {
    BVCheckOp(X,1,dotvec_local);
    nv = X->k-X->l;
    PetscCall(PetscObjectGetComm((PetscObject)X,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCheck(sr->state==STATE_BEGIN,PetscObjectComm((PetscObject)X),PETSC_ERR_ORDER,"Called before all VecxxxEnd() called");
    for (i=0;i<nv;i++) {
      if (sr->numopsbegin+i >= sr->maxops) PetscCall(PetscSplitReductionExtend(sr));
      sr->reducetype[sr->numopsbegin+i] = PETSC_SR_REDUCE_SUM;
      sr->invecs[sr->numopsbegin+i]     = (void*)X;
    }
    PetscCall(PetscLogEventBegin(BV_DotVec,X,y,0,0));
    PetscCall((*X->ops->dotvec_local)(X,y,sr->lvalues+sr->numopsbegin));
    sr->numopsbegin += nv;
    PetscCall(PetscLogEventEnd(BV_DotVec,X,y,0,0));
  }
  PetscFunctionReturn(0);
}

/*@
   BVDotVecEnd - Ends a split phase dot product computation.

   Input Parameters:
+  X - basis vectors
.  y - a vector
-  m - an array where the result will go

   Note:
   Each call to BVDotVecBegin() should be paired with a call to BVDotVecEnd().

   Level: advanced

.seealso: BVDotVecBegin(), BVDotVec()
@*/
PetscErrorCode BVDotVecEnd(BV X,Vec y,PetscScalar *m)
{
  PetscInt            i,nv;
  PetscSplitReduction *sr;
  MPI_Comm            comm;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidType(X,1);
  BVCheckSizes(X,1);

  if (X->ops->dotvec_end) PetscCall((*X->ops->dotvec_end)(X,y,m));
  else {
    nv = X->k-X->l;
    PetscCall(PetscObjectGetComm((PetscObject)X,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCall(PetscSplitReductionEnd(sr));

    PetscCheck(sr->numopsend<sr->numopsbegin,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Called VecxxxEnd() more times than VecxxxBegin()");
    PetscCheck((void*)X==sr->invecs[sr->numopsend],PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Called BVxxxEnd() in a different order or with a different BV than BVxxxBegin()");
    PetscCheck(sr->reducetype[sr->numopsend]==PETSC_SR_REDUCE_SUM,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Wrong type of reduction");
    for (i=0;i<nv;i++) m[i] = sr->gvalues[sr->numopsend++];

    /* Finished getting all the results so reset to no outstanding requests */
    if (sr->numopsend == sr->numopsbegin) {
      sr->state       = STATE_BEGIN;
      sr->numopsend   = 0;
      sr->numopsbegin = 0;
    }
  }
  PetscFunctionReturn(0);
}

/*@
   BVDotColumn - Computes multiple dot products of a column against all the
   previous columns of a BV.

   Collective on X

   Input Parameters:
+  X - basis vectors
-  j - the column index

   Output Parameter:
.  q - an array where the result must be placed

   Notes:
   This operation is equivalent to BVDotVec() but it uses column j of X
   rather than taking a Vec as an argument. The number of active columns of
   X is set to j before the computation, and restored afterwards.
   If X has leading columns specified, then these columns do not participate
   in the computation. Therefore, the length of array q must be equal to j
   minus the number of leading columns.

   Developer Notes:
   If q is NULL, then the result is written in position nc+l of the internal
   buffer vector, see BVGetBufferVec().

   Level: advanced

.seealso: BVDot(), BVDotVec(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVDotColumn(BV X,PetscInt j,PetscScalar *q)
{
  PetscInt       ksave;
  Vec            y;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(X,j,2);
  PetscValidType(X,1);
  BVCheckSizes(X,1);
  BVCheckOp(X,1,dotvec);

  PetscCheck(j>=0,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j must be non-negative");
  PetscCheck(j<X->m,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j=%" PetscInt_FMT " but BV only has %" PetscInt_FMT " columns",j,X->m);

  PetscCall(PetscLogEventBegin(BV_DotVec,X,0,0,0));
  ksave = X->k;
  X->k = j;
  if (!q && !X->buffer) PetscCall(BVGetBufferVec(X,&X->buffer));
  PetscCall(BVGetColumn(X,j,&y));
  PetscCall((*X->ops->dotvec)(X,y,q));
  PetscCall(BVRestoreColumn(X,j,&y));
  X->k = ksave;
  PetscCall(PetscLogEventEnd(BV_DotVec,X,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVDotColumnBegin - Starts a split phase dot product computation.

   Input Parameters:
+  X - basis vectors
.  j - the column index
-  m - an array where the result will go (can be NULL)

   Note:
   Each call to BVDotColumnBegin() should be paired with a call to BVDotColumnEnd().

   Level: advanced

.seealso: BVDotColumnEnd(), BVDotColumn()
@*/
PetscErrorCode BVDotColumnBegin(BV X,PetscInt j,PetscScalar *m)
{
  PetscInt            i,nv,ksave;
  PetscSplitReduction *sr;
  MPI_Comm            comm;
  Vec                 y;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(X,j,2);
  PetscValidType(X,1);
  BVCheckSizes(X,1);

  PetscCheck(j>=0,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j must be non-negative");
  PetscCheck(j<X->m,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j=%" PetscInt_FMT " but BV only has %" PetscInt_FMT " columns",j,X->m);
  ksave = X->k;
  X->k = j;
  PetscCall(BVGetColumn(X,j,&y));

  if (X->ops->dotvec_begin) PetscCall((*X->ops->dotvec_begin)(X,y,m));
  else {
    BVCheckOp(X,1,dotvec_local);
    nv = X->k-X->l;
    PetscCall(PetscObjectGetComm((PetscObject)X,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCheck(sr->state==STATE_BEGIN,PetscObjectComm((PetscObject)X),PETSC_ERR_ORDER,"Called before all VecxxxEnd() called");
    for (i=0;i<nv;i++) {
      if (sr->numopsbegin+i >= sr->maxops) PetscCall(PetscSplitReductionExtend(sr));
      sr->reducetype[sr->numopsbegin+i] = PETSC_SR_REDUCE_SUM;
      sr->invecs[sr->numopsbegin+i]     = (void*)X;
    }
    PetscCall(PetscLogEventBegin(BV_DotVec,X,0,0,0));
    PetscCall((*X->ops->dotvec_local)(X,y,sr->lvalues+sr->numopsbegin));
    sr->numopsbegin += nv;
    PetscCall(PetscLogEventEnd(BV_DotVec,X,0,0,0));
  }
  PetscCall(BVRestoreColumn(X,j,&y));
  X->k = ksave;
  PetscFunctionReturn(0);
}

/*@
   BVDotColumnEnd - Ends a split phase dot product computation.

   Input Parameters:
+  X - basis vectors
.  j - the column index
-  m - an array where the result will go

   Notes:
   Each call to BVDotColumnBegin() should be paired with a call to BVDotColumnEnd().

   Level: advanced

.seealso: BVDotColumnBegin(), BVDotColumn()
@*/
PetscErrorCode BVDotColumnEnd(BV X,PetscInt j,PetscScalar *m)
{
  PetscInt            i,nv,ksave;
  PetscSplitReduction *sr;
  MPI_Comm            comm;
  Vec                 y;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(X,j,2);
  PetscValidType(X,1);
  BVCheckSizes(X,1);

  PetscCheck(j>=0,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j must be non-negative");
  PetscCheck(j<X->m,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_OUTOFRANGE,"Index j=%" PetscInt_FMT " but BV only has %" PetscInt_FMT " columns",j,X->m);
  ksave = X->k;
  X->k = j;

  if (X->ops->dotvec_end) {
    PetscCall(BVGetColumn(X,j,&y));
    PetscCall((*X->ops->dotvec_end)(X,y,m));
    PetscCall(BVRestoreColumn(X,j,&y));
  } else {
    nv = X->k-X->l;
    PetscCall(PetscObjectGetComm((PetscObject)X,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCall(PetscSplitReductionEnd(sr));

    PetscCheck(sr->numopsend<sr->numopsbegin,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Called VecxxxEnd() more times than VecxxxBegin()");
    PetscCheck((void*)X==sr->invecs[sr->numopsend],PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Called BVxxxEnd() in a different order or with a different BV than BVxxxBegin()");
    PetscCheck(sr->reducetype[sr->numopsend]==PETSC_SR_REDUCE_SUM,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_WRONGSTATE,"Wrong type of reduction");
    for (i=0;i<nv;i++) m[i] = sr->gvalues[sr->numopsend++];

    /* Finished getting all the results so reset to no outstanding requests */
    if (sr->numopsend == sr->numopsbegin) {
      sr->state       = STATE_BEGIN;
      sr->numopsend   = 0;
      sr->numopsbegin = 0;
    }
  }
  X->k = ksave;
  PetscFunctionReturn(0);
}

static inline PetscErrorCode BVNorm_Private(BV bv,Vec z,NormType type,PetscReal *val)
{
  PetscScalar    p;

  PetscFunctionBegin;
  PetscCall(BV_IPMatMult(bv,z));
  PetscCall(VecDot(bv->Bx,z,&p));
  PetscCall(BV_SafeSqrt(bv,p,val));
  PetscFunctionReturn(0);
}

static inline PetscErrorCode BVNorm_Begin_Private(BV bv,Vec z,NormType type,PetscReal *val)
{
  PetscScalar    p;

  PetscFunctionBegin;
  PetscCall(BV_IPMatMult(bv,z));
  PetscCall(VecDotBegin(bv->Bx,z,&p));
  PetscFunctionReturn(0);
}

static inline PetscErrorCode BVNorm_End_Private(BV bv,Vec z,NormType type,PetscReal *val)
{
  PetscScalar    p;

  PetscFunctionBegin;
  PetscCall(VecDotEnd(bv->Bx,z,&p));
  PetscCall(BV_SafeSqrt(bv,p,val));
  PetscFunctionReturn(0);
}

/*@
   BVNorm - Computes the matrix norm of the BV.

   Collective on bv

   Input Parameters:
+  bv   - basis vectors
-  type - the norm type

   Output Parameter:
.  val  - the norm

   Notes:
   All active columns (except the leading ones) are considered as a matrix.
   The allowed norms are NORM_1, NORM_FROBENIUS, and NORM_INFINITY.

   This operation fails if a non-standard inner product has been
   specified with BVSetMatrix().

   Level: intermediate

.seealso: BVNormVec(), BVNormColumn(), BVNormalize(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVNorm(BV bv,NormType type,PetscReal *val)
{
  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidLogicalCollectiveEnum(bv,type,2);
  PetscValidRealPointer(val,3);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCheck(type!=NORM_2 && type!=NORM_1_AND_2,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");
  PetscCheck(!bv->matrix,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Matrix norm not available for non-standard inner product");

  PetscCall(PetscLogEventBegin(BV_Norm,bv,0,0,0));
  PetscCall((*bv->ops->norm)(bv,-1,type,val));
  PetscCall(PetscLogEventEnd(BV_Norm,bv,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVNormVec - Computes the norm of a given vector.

   Collective on bv

   Input Parameters:
+  bv   - basis vectors
.  v    - the vector
-  type - the norm type

   Output Parameter:
.  val  - the norm

   Notes:
   This is the analogue of BVNormColumn() but for a vector that is not in the BV.
   If a non-standard inner product has been specified with BVSetMatrix(),
   then the returned value is sqrt(v'*B*v), where B is the inner product
   matrix (argument 'type' is ignored). Otherwise, VecNorm() is called.

   Level: developer

.seealso: BVNorm(), BVNormColumn(), BVSetMatrix()
@*/
PetscErrorCode BVNormVec(BV bv,Vec v,NormType type,PetscReal *val)
{
  PetscInt       n;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidHeaderSpecific(v,VEC_CLASSID,2);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);
  PetscValidType(v,2);
  PetscCheckSameComm(bv,1,v,2);

  PetscCheck(type!=NORM_1_AND_2 || bv->matrix,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  PetscCall(PetscLogEventBegin(BV_NormVec,bv,0,0,0));
  if (bv->matrix) { /* non-standard inner product */
    PetscCall(VecGetLocalSize(v,&n));
    PetscCheck(bv->n==n,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension bv %" PetscInt_FMT ", v %" PetscInt_FMT,bv->n,n);
    PetscCall(BVNorm_Private(bv,v,type,val));
  } else PetscCall(VecNorm(v,type,val));
  PetscCall(PetscLogEventEnd(BV_NormVec,bv,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVNormVecBegin - Starts a split phase norm computation.

   Input Parameters:
+  bv   - basis vectors
.  v    - the vector
.  type - the norm type
-  val  - the norm

   Note:
   Each call to BVNormVecBegin() should be paired with a call to BVNormVecEnd().

   Level: advanced

.seealso: BVNormVecEnd(), BVNormVec()
@*/
PetscErrorCode BVNormVecBegin(BV bv,Vec v,NormType type,PetscReal *val)
{
  PetscInt       n;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidHeaderSpecific(v,VEC_CLASSID,2);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);
  PetscValidType(v,2);
  PetscCheckSameTypeAndComm(bv,1,v,2);

  PetscCheck(type!=NORM_1_AND_2 || bv->matrix,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  PetscCall(PetscLogEventBegin(BV_NormVec,bv,0,0,0));
  if (bv->matrix) { /* non-standard inner product */
    PetscCall(VecGetLocalSize(v,&n));
    PetscCheck(bv->n==n,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension bv %" PetscInt_FMT ", v %" PetscInt_FMT,bv->n,n);
    PetscCall(BVNorm_Begin_Private(bv,v,type,val));
  } else PetscCall(VecNormBegin(v,type,val));
  PetscCall(PetscLogEventEnd(BV_NormVec,bv,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVNormVecEnd - Ends a split phase norm computation.

   Input Parameters:
+  bv   - basis vectors
.  v    - the vector
.  type - the norm type
-  val  - the norm

   Note:
   Each call to BVNormVecBegin() should be paired with a call to BVNormVecEnd().

   Level: advanced

.seealso: BVNormVecBegin(), BVNormVec()
@*/
PetscErrorCode BVNormVecEnd(BV bv,Vec v,NormType type,PetscReal *val)
{
  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCheck(type!=NORM_1_AND_2,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  if (bv->matrix) PetscCall(BVNorm_End_Private(bv,v,type,val));  /* non-standard inner product */
  else PetscCall(VecNormEnd(v,type,val));
  PetscFunctionReturn(0);
}

/*@
   BVNormColumn - Computes the vector norm of a selected column.

   Collective on bv

   Input Parameters:
+  bv   - basis vectors
.  j    - column number to be used
-  type - the norm type

   Output Parameter:
.  val  - the norm

   Notes:
   The norm of V[j] is computed (NORM_1, NORM_2, or NORM_INFINITY).
   If a non-standard inner product has been specified with BVSetMatrix(),
   then the returned value is sqrt(V[j]'*B*V[j]),
   where B is the inner product matrix (argument 'type' is ignored).

   Level: intermediate

.seealso: BVNorm(), BVNormVec(), BVNormalize(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVNormColumn(BV bv,PetscInt j,NormType type,PetscReal *val)
{
  Vec            z;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(bv,j,2);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCheck(j>=0 && j<bv->m,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_OUTOFRANGE,"Argument j has wrong value %" PetscInt_FMT ", the number of columns is %" PetscInt_FMT,j,bv->m);
  PetscCheck(type!=NORM_1_AND_2 || bv->matrix,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  PetscCall(PetscLogEventBegin(BV_NormVec,bv,0,0,0));
  if (bv->matrix) { /* non-standard inner product */
    PetscCall(BVGetColumn(bv,j,&z));
    PetscCall(BVNorm_Private(bv,z,type,val));
    PetscCall(BVRestoreColumn(bv,j,&z));
  } else PetscCall((*bv->ops->norm)(bv,j,type,val));
  PetscCall(PetscLogEventEnd(BV_NormVec,bv,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVNormColumnBegin - Starts a split phase norm computation.

   Input Parameters:
+  bv   - basis vectors
.  j    - column number to be used
.  type - the norm type
-  val  - the norm

   Note:
   Each call to BVNormColumnBegin() should be paired with a call to BVNormColumnEnd().

   Level: advanced

.seealso: BVNormColumnEnd(), BVNormColumn()
@*/
PetscErrorCode BVNormColumnBegin(BV bv,PetscInt j,NormType type,PetscReal *val)
{
  PetscSplitReduction *sr;
  PetscReal           lresult;
  MPI_Comm            comm;
  Vec                 z;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(bv,j,2);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCheck(j>=0 && j<bv->m,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_OUTOFRANGE,"Argument j has wrong value %" PetscInt_FMT ", the number of columns is %" PetscInt_FMT,j,bv->m);
  PetscCheck(type!=NORM_1_AND_2 || bv->matrix,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  PetscCall(PetscLogEventBegin(BV_NormVec,bv,0,0,0));
  PetscCall(BVGetColumn(bv,j,&z));
  if (bv->matrix) PetscCall(BVNorm_Begin_Private(bv,z,type,val)); /* non-standard inner product */
  else if (bv->ops->norm_begin) PetscCall((*bv->ops->norm_begin)(bv,j,type,val));
  else {
    BVCheckOp(bv,1,norm_local);
    PetscCall(PetscObjectGetComm((PetscObject)z,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCheck(sr->state==STATE_BEGIN,PetscObjectComm((PetscObject)bv),PETSC_ERR_ORDER,"Called before all VecxxxEnd() called");
    if (sr->numopsbegin >= sr->maxops) PetscCall(PetscSplitReductionExtend(sr));
    sr->invecs[sr->numopsbegin] = (void*)bv;
    PetscCall((*bv->ops->norm_local)(bv,j,type,&lresult));
    if (type == NORM_2) lresult = lresult*lresult;
    if (type == NORM_MAX) sr->reducetype[sr->numopsbegin] = PETSC_SR_REDUCE_MAX;
    else sr->reducetype[sr->numopsbegin] = PETSC_SR_REDUCE_SUM;
    sr->lvalues[sr->numopsbegin++] = lresult;
  }
  PetscCall(BVRestoreColumn(bv,j,&z));
  PetscCall(PetscLogEventEnd(BV_NormVec,bv,0,0,0));
  PetscFunctionReturn(0);
}

/*@
   BVNormColumnEnd - Ends a split phase norm computation.

   Input Parameters:
+  bv   - basis vectors
.  j    - column number to be used
.  type - the norm type
-  val  - the norm

   Note:
   Each call to BVNormColumnBegin() should be paired with a call to BVNormColumnEnd().

   Level: advanced

.seealso: BVNormColumnBegin(), BVNormColumn()
@*/
PetscErrorCode BVNormColumnEnd(BV bv,PetscInt j,NormType type,PetscReal *val)
{
  PetscSplitReduction *sr;
  MPI_Comm            comm;
  Vec                 z;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidLogicalCollectiveInt(bv,j,2);
  PetscValidLogicalCollectiveEnum(bv,type,3);
  PetscValidRealPointer(val,4);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCheck(type!=NORM_1_AND_2,PetscObjectComm((PetscObject)bv),PETSC_ERR_SUP,"Requested norm not available");

  PetscCall(BVGetColumn(bv,j,&z));
  if (bv->matrix) PetscCall(BVNorm_End_Private(bv,z,type,val)); /* non-standard inner product */
  else if (bv->ops->norm_end) PetscCall((*bv->ops->norm_end)(bv,j,type,val));
  else {
    PetscCall(PetscObjectGetComm((PetscObject)z,&comm));
    PetscCall(PetscSplitReductionGet(comm,&sr));
    PetscCall(PetscSplitReductionEnd(sr));

    PetscCheck(sr->numopsend<sr->numopsbegin,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_WRONGSTATE,"Called VecxxxEnd() more times then VecxxxBegin()");
    PetscCheck((void*)bv==sr->invecs[sr->numopsend],PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_WRONGSTATE,"Called VecxxxEnd() in a different order or with a different vector than VecxxxBegin()");
    PetscCheck(sr->reducetype[sr->numopsend]==PETSC_SR_REDUCE_MAX || type!=NORM_MAX,PetscObjectComm((PetscObject)bv),PETSC_ERR_ARG_WRONGSTATE,"Called BVNormEnd(,NORM_MAX,) on a reduction started with VecDotBegin() or NORM_1 or NORM_2");
    *val = PetscRealPart(sr->gvalues[sr->numopsend++]);
    if (type == NORM_2) *val = PetscSqrtReal(*val);
    if (sr->numopsend == sr->numopsbegin) {
      sr->state       = STATE_BEGIN;
      sr->numopsend   = 0;
      sr->numopsbegin = 0;
    }
  }
  PetscCall(BVRestoreColumn(bv,j,&z));
  PetscFunctionReturn(0);
}

/*@
   BVNormalize - Normalize all columns (starting from the leading ones).

   Collective on bv

   Input Parameters:
+  bv   - basis vectors
-  eigi - (optional) imaginary parts of eigenvalues

   Notes:
   On output, all columns will have unit norm. The normalization is done with
   respect to the 2-norm, or to the B-norm if a non-standard inner product has
   been specified with BVSetMatrix(), see BVNormColumn().

   If the optional argument eigi is passed (taken into account only in real
   scalars) it is interpreted as the imaginary parts of the eigenvalues and
   the BV is supposed to contain the corresponding eigenvectors. Suppose the
   first three values are eigi = { 0, alpha, -alpha }, then the first column
   is normalized as usual, but the second and third ones are normalized assuming
   that they contain the real and imaginary parts of a complex conjugate pair of
   eigenvectors.

   If eigi is passed, the inner-product matrix is ignored.

   If there are leading columns, they are not modified (are assumed to be already
   normalized).

   Level: intermediate

.seealso: BVNormColumn()
@*/
PetscErrorCode BVNormalize(BV bv,PetscScalar *eigi)
{
  PetscReal      norm;
  PetscInt       i;
  Vec            v;
#if !defined(PETSC_USE_COMPLEX)
  Vec            v1;
#endif

  PetscFunctionBegin;
  PetscValidHeaderSpecific(bv,BV_CLASSID,1);
  PetscValidType(bv,1);
  BVCheckSizes(bv,1);

  PetscCall(PetscLogEventBegin(BV_Normalize,bv,0,0,0));
  if (bv->matrix && !eigi) {
    for (i=bv->l;i<bv->k;i++) {
      PetscCall(BVNormColumn(bv,i,NORM_2,&norm));
      PetscCall(BVScaleColumn(bv,i,1.0/norm));
    }
  } else if (bv->ops->normalize) PetscCall((*bv->ops->normalize)(bv,eigi));
  else {
    for (i=bv->l;i<bv->k;i++) {
#if !defined(PETSC_USE_COMPLEX)
      if (eigi && eigi[i] != 0.0) {
        PetscCall(BVGetColumn(bv,i,&v));
        PetscCall(BVGetColumn(bv,i+1,&v1));
        PetscCall(VecNormalizeComplex(v,v1,PETSC_TRUE,NULL));
        PetscCall(BVRestoreColumn(bv,i,&v));
        PetscCall(BVRestoreColumn(bv,i+1,&v1));
        i++;
      } else
#endif
      {
        PetscCall(BVGetColumn(bv,i,&v));
        PetscCall(VecNormalize(v,NULL));
        PetscCall(BVRestoreColumn(bv,i,&v));
      }
    }
  }
  PetscCall(PetscLogEventEnd(BV_Normalize,bv,0,0,0));
  PetscCall(PetscObjectStateIncrease((PetscObject)bv));
  PetscFunctionReturn(0);
}

/*
  Compute Y^H*A*X: right part column by column (with MatMult) and bottom
  part row by row (with MatMultHermitianTranspose); result placed in marray[*,ldm]
*/
static inline PetscErrorCode BVMatProject_Vec(BV X,Mat A,BV Y,PetscScalar *marray,PetscInt ldm,PetscBool symm)
{
  PetscInt       i,j,lx,ly,kx,ky,ulim;
  Vec            z,f;

  PetscFunctionBegin;
  lx = X->l; kx = X->k;
  ly = Y->l; ky = Y->k;
  PetscCall(BVCreateVec(X,&f));
  BVCheckOp(Y,3,dotvec);
  for (j=lx;j<kx;j++) {
    PetscCall(BVGetColumn(X,j,&z));
    PetscCall(MatMult(A,z,f));
    PetscCall(BVRestoreColumn(X,j,&z));
    ulim = PetscMin(ly+(j-lx)+1,ky);
    Y->l = 0; Y->k = ulim;
    PetscCall((*Y->ops->dotvec)(Y,f,marray+j*ldm));
    if (symm) {
      for (i=0;i<j;i++) marray[j+i*ldm] = PetscConj(marray[i+j*ldm]);
    }
  }
  if (!symm) {
    BVCheckOp(X,1,dotvec);
    PetscCall(BV_AllocateCoeffs(Y));
    for (j=ly;j<ky;j++) {
      PetscCall(BVGetColumn(Y,j,&z));
      PetscCall(MatMultHermitianTranspose(A,z,f));
      PetscCall(BVRestoreColumn(Y,j,&z));
      ulim = PetscMin(lx+(j-ly),kx);
      X->l = 0; X->k = ulim;
      PetscCall((*X->ops->dotvec)(X,f,Y->h));
      for (i=0;i<ulim;i++) marray[j+i*ldm] = PetscConj(Y->h[i]);
    }
  }
  PetscCall(VecDestroy(&f));
  X->l = lx; X->k = kx;
  Y->l = ly; Y->k = ky;
  PetscFunctionReturn(0);
}

/*
  Compute Y^H*A*X= [   --   | Y0'*W1 ]
                   [ Y1'*W0 | Y1'*W1 ]
  Allocates auxiliary BV to store the result of A*X, then one BVDot
  call for top-right part and another one for bottom part;
  result placed in marray[*,ldm]
*/
static inline PetscErrorCode BVMatProject_MatMult(BV X,Mat A,BV Y,PetscScalar *marray,PetscInt ldm)
{
  PetscInt          j,lx,ly,kx,ky;
  const PetscScalar *harray;
  Mat               H;
  BV                W;

  PetscFunctionBegin;
  lx = X->l; kx = X->k;
  ly = Y->l; ky = Y->k;
  PetscCall(BVDuplicate(X,&W));
  X->l = 0; X->k = kx;
  W->l = 0; W->k = kx;
  PetscCall(BVMatMult(X,A,W));

  /* top-right part, Y0'*AX1 */
  if (ly>0 && lx<kx) {
    PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,ly,kx,NULL,&H));
    W->l = lx; W->k = kx;
    Y->l = 0;  Y->k = ly;
    PetscCall(BVDot(W,Y,H));
    PetscCall(MatDenseGetArrayRead(H,&harray));
    for (j=lx;j<kx;j++) PetscCall(PetscArraycpy(marray+j*ldm,harray+j*ly,ly));
    PetscCall(MatDenseRestoreArrayRead(H,&harray));
    PetscCall(MatDestroy(&H));
  }

  /* bottom part, Y1'*AX */
  if (kx>0 && ly<ky) {
    PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,ky,kx,NULL,&H));
    W->l = 0;  W->k = kx;
    Y->l = ly; Y->k = ky;
    PetscCall(BVDot(W,Y,H));
    PetscCall(MatDenseGetArrayRead(H,&harray));
    for (j=0;j<kx;j++) PetscCall(PetscArraycpy(marray+j*ldm+ly,harray+j*ky+ly,ky-ly));
    PetscCall(MatDenseRestoreArrayRead(H,&harray));
    PetscCall(MatDestroy(&H));
  }
  PetscCall(BVDestroy(&W));
  X->l = lx; X->k = kx;
  Y->l = ly; Y->k = ky;
  PetscFunctionReturn(0);
}

/*
  Compute Y^H*A*X= [   --   | Y0'*W1 ]
                   [ Y1'*W0 | Y1'*W1 ]
  First stage: allocate auxiliary BV to store A*X1, one BVDot for right part;
  Second stage: resize BV to accommodate A'*Y1, then call BVDot for transpose of
  bottom-left part; result placed in marray[*,ldm]
*/
static inline PetscErrorCode BVMatProject_MatMult_2(BV X,Mat A,BV Y,PetscScalar *marray,PetscInt ldm,PetscBool symm)
{
  PetscInt          i,j,lx,ly,kx,ky;
  const PetscScalar *harray;
  Mat               H;
  BV                W;

  PetscFunctionBegin;
  lx = X->l; kx = X->k;
  ly = Y->l; ky = Y->k;

  /* right part, Y'*AX1 */
  PetscCall(BVDuplicateResize(X,kx-lx,&W));
  if (ky>0 && lx<kx) {
    PetscCall(BVMatMult(X,A,W));
    PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,ky,kx-lx,NULL,&H));
    Y->l = 0; Y->k = ky;
    PetscCall(BVDot(W,Y,H));
    PetscCall(MatDenseGetArrayRead(H,&harray));
    for (j=lx;j<kx;j++) PetscCall(PetscArraycpy(marray+j*ldm,harray+(j-lx)*ky,ky));
    PetscCall(MatDenseRestoreArrayRead(H,&harray));
    PetscCall(MatDestroy(&H));
  }

  /* bottom-left part, Y1'*AX0 */
  if (lx>0 && ly<ky) {
    if (symm) {
      /* do not compute, just copy symmetric elements */
      for (i=ly;i<ky;i++) {
        for (j=0;j<lx;j++) marray[i+j*ldm] = PetscConj(marray[j+i*ldm]);
      }
    } else {
      PetscCall(BVResize(W,ky-ly,PETSC_FALSE));
      Y->l = ly; Y->k = ky;
      PetscCall(BVMatMultHermitianTranspose(Y,A,W));
      PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,lx,ky-ly,NULL,&H));
      X->l = 0; X->k = lx;
      PetscCall(BVDot(W,X,H));
      PetscCall(MatDenseGetArrayRead(H,&harray));
      for (i=0;i<ky-ly;i++) {
        for (j=0;j<lx;j++) {
          marray[i+j*ldm+ly] = PetscConj(harray[j+i*(ky-ly)]);
        }
      }
      PetscCall(MatDenseRestoreArrayRead(H,&harray));
      PetscCall(MatDestroy(&H));
    }
  }
  PetscCall(BVDestroy(&W));
  X->l = lx; X->k = kx;
  Y->l = ly; Y->k = ky;
  PetscFunctionReturn(0);
}

/*
  Compute Y^H*X = [   --   | Y0'*X1 ]     (X contains A*X):
                  [ Y1'*X0 | Y1'*X1 ]
  one BVDot call for top-right part and another one for bottom part;
  result placed in marray[*,ldm]
*/
static inline PetscErrorCode BVMatProject_Dot(BV X,BV Y,PetscScalar *marray,PetscInt ldm)
{
  PetscInt          j,lx,ly,kx,ky;
  const PetscScalar *harray;
  Mat               H;

  PetscFunctionBegin;
  lx = X->l; kx = X->k;
  ly = Y->l; ky = Y->k;

  /* top-right part, Y0'*X1 */
  if (ly>0 && lx<kx) {
    PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,ly,kx,NULL,&H));
    X->l = lx; X->k = kx;
    Y->l = 0;  Y->k = ly;
    PetscCall(BVDot(X,Y,H));
    PetscCall(MatDenseGetArrayRead(H,&harray));
    for (j=lx;j<kx;j++) PetscCall(PetscArraycpy(marray+j*ldm,harray+j*ly,ly));
    PetscCall(MatDenseRestoreArrayRead(H,&harray));
    PetscCall(MatDestroy(&H));
  }

  /* bottom part, Y1'*X */
  if (kx>0 && ly<ky) {
    PetscCall(MatCreateSeqDense(PETSC_COMM_SELF,ky,kx,NULL,&H));
    X->l = 0;  X->k = kx;
    Y->l = ly; Y->k = ky;
    PetscCall(BVDot(X,Y,H));
    PetscCall(MatDenseGetArrayRead(H,&harray));
    for (j=0;j<kx;j++) PetscCall(PetscArraycpy(marray+j*ldm+ly,harray+j*ky+ly,ky-ly));
    PetscCall(MatDenseRestoreArrayRead(H,&harray));
    PetscCall(MatDestroy(&H));
  }
  X->l = lx; X->k = kx;
  Y->l = ly; Y->k = ky;
  PetscFunctionReturn(0);
}

/*@
   BVMatProject - Computes the projection of a matrix onto a subspace.

   Collective on X

   Input Parameters:
+  X - basis vectors
.  A - (optional) matrix to be projected
.  Y - left basis vectors, can be equal to X
-  M - Mat object where the result must be placed

   Output Parameter:
.  M - the resulting matrix

   Notes:
   If A=NULL, then it is assumed that X already contains A*X.

   This operation is similar to BVDot(), with important differences.
   The goal is to compute the matrix resulting from the orthogonal projection
   of A onto the subspace spanned by the columns of X, M = X^H*A*X, or the
   oblique projection onto X along Y, M = Y^H*A*X.

   A difference with respect to BVDot() is that the standard inner product
   is always used, regardless of a non-standard inner product being specified
   with BVSetMatrix().

   On entry, M must be a sequential dense Mat with dimensions ky,kx at least,
   where ky (resp. kx) is the number of active columns of Y (resp. X).
   Another difference with respect to BVDot() is that all entries of M are
   computed except the leading ly,lx part, where ly (resp. lx) is the
   number of leading columns of Y (resp. X). Hence, the leading columns of
   X and Y participate in the computation, as opposed to BVDot().
   The leading part of M is assumed to be already available from previous
   computations.

   In the orthogonal projection case, Y=X, some computation can be saved if
   A is real symmetric (or complex Hermitian). In order to exploit this
   property, the symmetry flag of A must be set with MatSetOption().

   Level: intermediate

.seealso: BVDot(), BVSetActiveColumns(), BVSetMatrix()
@*/
PetscErrorCode BVMatProject(BV X,Mat A,BV Y,Mat M)
{
  PetscBool      set,flg,symm=PETSC_FALSE;
  PetscInt       m,n,ldm;
  PetscScalar    *marray;
  Mat            Xmatrix,Ymatrix;
  PetscObjectId  idx,idy;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(X,BV_CLASSID,1);
  if (A) PetscValidHeaderSpecific(A,MAT_CLASSID,2);
  PetscValidHeaderSpecific(Y,BV_CLASSID,3);
  PetscValidHeaderSpecific(M,MAT_CLASSID,4);
  PetscValidType(X,1);
  BVCheckSizes(X,1);
  if (A) {
    PetscValidType(A,2);
    PetscCheckSameComm(X,1,A,2);
  }
  PetscValidType(Y,3);
  BVCheckSizes(Y,3);
  PetscValidType(M,4);
  PetscCheckSameTypeAndComm(X,1,Y,3);
  PetscCheckTypeNames(M,MATSEQDENSE,MATSEQDENSECUDA);

  PetscCall(MatGetSize(M,&m,&n));
  PetscCall(MatDenseGetLDA(M,&ldm));
  PetscCheck(m>=Y->k,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_SIZ,"Matrix M has %" PetscInt_FMT " rows, should have at least %" PetscInt_FMT,m,Y->k);
  PetscCheck(n>=X->k,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_SIZ,"Matrix M has %" PetscInt_FMT " columns, should have at least %" PetscInt_FMT,n,X->k);
  PetscCheck(X->n==Y->n,PetscObjectComm((PetscObject)X),PETSC_ERR_ARG_INCOMP,"Mismatching local dimension X %" PetscInt_FMT ", Y %" PetscInt_FMT,X->n,Y->n);

  PetscCall(PetscLogEventBegin(BV_MatProject,X,A,Y,0));
  /* temporarily set standard inner product */
  Xmatrix = X->matrix;
  Ymatrix = Y->matrix;
  X->matrix = Y->matrix = NULL;

  PetscCall(PetscObjectGetId((PetscObject)X,&idx));
  PetscCall(PetscObjectGetId((PetscObject)Y,&idy));
  if (A && idx==idy) { /* check symmetry of M=X'AX */
    PetscCall(MatIsHermitianKnown(A,&set,&flg));
    symm = set? flg: PETSC_FALSE;
  }

  PetscCall(MatDenseGetArray(M,&marray));

  if (A) {
    if (X->vmm==BV_MATMULT_VECS) {
      /* perform computation column by column */
      PetscCall(BVMatProject_Vec(X,A,Y,marray,ldm,symm));
    } else {
      /* use BVMatMult, then BVDot */
      PetscCall(MatHasOperation(A,MATOP_MULT_TRANSPOSE,&flg));
      if (symm || (flg && X->l>=X->k/2 && Y->l>=Y->k/2)) PetscCall(BVMatProject_MatMult_2(X,A,Y,marray,ldm,symm));
      else PetscCall(BVMatProject_MatMult(X,A,Y,marray,ldm));
    }
  } else {
    /* use BVDot on subblocks */
    PetscCall(BVMatProject_Dot(X,Y,marray,ldm));
  }

  PetscCall(MatDenseRestoreArray(M,&marray));
  PetscCall(PetscLogEventEnd(BV_MatProject,X,A,Y,0));
  /* restore non-standard inner product */
  X->matrix = Xmatrix;
  Y->matrix = Ymatrix;
  PetscFunctionReturn(0);
}
