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/*                      

   SLEPc eigensolver: "subspace"

   Method: Subspace Iteration

   Algorithm:

       Subspace iteration with Rayleigh-Ritz projection and locking,

       based on the SRRIT implementation.

   References:

       [1] "Subspace Iteration in SLEPc", SLEPc Technical Report STR-3,

           available at http://www.grycap.upv.es/slepc.

   Last update: June 2004

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      SLEPc - Scalable Library for Eigenvalue Problem Computations

      Copyright (c) 2002-2007, Universidad Politecnica de Valencia, Spain

      This file is part of SLEPc. See the README file for conditions of use

      and additional information.

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

*/

#include "src/eps/epsimpl.h"                /*I "slepceps.h" I*/

#include "slepcblaslapack.h"

#undef __FUNCT__  

#define __FUNCT__ "EPSSetUp_SUBSPACE"

PetscErrorCode EPSSetUp_SUBSPACE(EPS eps)

{

  PetscErrorCode ierr;

  PetscInt       N;

  PetscFunctionBegin;

  ierr = VecGetSize(eps->IV[0],&N);CHKERRQ(ierr);

  if (eps->ncv) {

    if (eps->ncv<eps->nev) SETERRQ(1,"The value of ncv must be at least nev");

  }

  else eps->ncv = PetscMin(N,PetscMax(2*eps->nev,eps->nev+15));

  if (!eps->max_it) eps->max_it = PetscMax(100,2*N/eps->ncv);

  if (eps->which!=EPS_LARGEST_MAGNITUDE)

    SETERRQ(1,"Wrong value of eps->which");

  ierr = EPSAllocateSolution(eps);CHKERRQ(ierr);

  ierr = PetscFree(eps->T);CHKERRQ(ierr);

  ierr = PetscMalloc(eps->ncv*eps->ncv*sizeof(PetscScalar),&eps->T);CHKERRQ(ierr);

  ierr = EPSDefaultGetWork(eps,eps->ncv);CHKERRQ(ierr);

  PetscFunctionReturn(0);

}

#undef __FUNCT__  

#define __FUNCT__ "EPSHessCond"

/*

   EPSHessCond - Compute the inf-norm condition number of the upper

   Hessenberg matrix H: cond(H) = norm(H)*norm(inv(H)).

   This routine uses Gaussian elimination with partial pivoting to

   compute the inverse explicitly.

*/

static PetscErrorCode EPSHessCond(PetscScalar* H,int n, PetscReal* cond)

{

#if defined(PETSC_MISSING_LAPACK_GETRF) || defined(SLEPC_MISSING_LAPACK_GETRI) || defined(SLEPC_MISSING_LAPACK_LANGE) || defined(SLEPC_MISSING_LAPACK_LANHS)

  PetscFunctionBegin;

  SETERRQ(PETSC_ERR_SUP,"GETRF,GETRI - Lapack routines are unavailable.");

#else

  PetscErrorCode ierr;

  int            *ipiv,lwork,info;

  PetscScalar    *work;

  PetscReal      hn,hin,*rwork;

  PetscFunctionBegin;

  ierr = PetscLogEventBegin(EPS_Dense,0,0,0,0);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(int)*n,&ipiv);CHKERRQ(ierr);

  lwork = n*n;

  ierr = PetscMalloc(sizeof(PetscScalar)*lwork,&work);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(PetscReal)*n,&rwork);CHKERRQ(ierr);

  hn = LAPACKlanhs_("I",&n,H,&n,rwork,1);

  LAPACKgetrf_(&n,&n,H,&n,ipiv,&info);

  if (info) SETERRQ1(PETSC_ERR_LIB,"Error in Lapack xGETRF %d",info);

  LAPACKgetri_(&n,H,&n,ipiv,work,&lwork,&info);

  if (info) SETERRQ1(PETSC_ERR_LIB,"Error in Lapack xGETRI %d",info);

  hin = LAPACKlange_("I",&n,&n,H,&n,rwork,1);

  *cond = hn * hin;

  ierr = PetscFree(ipiv);CHKERRQ(ierr);

  ierr = PetscFree(work);CHKERRQ(ierr);

  ierr = PetscFree(rwork);CHKERRQ(ierr);

  ierr = PetscLogEventEnd(EPS_Dense,0,0,0,0);CHKERRQ(ierr);

  PetscFunctionReturn(0);

#endif

}

#undef __FUNCT__  

#define __FUNCT__ "EPSFindGroup"

/*

   EPSFindGroup - Find a group of nearly equimodular eigenvalues, provided

   in arrays wr and wi, according to the tolerance grptol. Also the 2-norms

   of the residuals must be passed-in (rsd). Arrays are processed from index

   l to index m only. The output information is:

   ngrp - number of entries of the group

   ctr  - (w(l)+w(l+ngrp-1))/2

   ae   - average of wr(l),...,wr(l+ngrp-1)

   arsd - average of rsd(l),...,rsd(l+ngrp-1)

*/

static PetscErrorCode EPSFindGroup(int l,int m,PetscScalar *wr,PetscScalar *wi,PetscReal *rsd,

  PetscReal grptol,int *ngrp,PetscReal *ctr,PetscReal *ae,PetscReal *arsd)

{

  int       i;

  PetscReal rmod,rmod1;

  PetscFunctionBegin;

  *ngrp = 0;

  *ctr = 0;

  rmod = SlepcAbsEigenvalue(wr[l],wi[l]);

  for (i=l;i<m;) {

    rmod1 = SlepcAbsEigenvalue(wr[i],wi[i]);

    if (PetscAbsReal(rmod-rmod1) > grptol*(rmod+rmod1)) break;

    *ctr = (rmod+rmod1)/2.0;

    if (wi[i] != 0.0) {

      (*ngrp)+=2;

      i+=2;

    } else {

      (*ngrp)++;

      i++;

    }

  }

  *ae = 0;

  *arsd = 0;

  if (*ngrp) {

    for (i=l;i<l+*ngrp;i++) {

      (*ae) += PetscRealPart(wr[i]);

      (*arsd) += rsd[i]*rsd[i];

    }

    *ae = *ae / *ngrp;

    *arsd = PetscSqrtScalar(*arsd / *ngrp);

  }

  PetscFunctionReturn(0);

}

#undef __FUNCT__  

#define __FUNCT__ "EPSSchurResidualNorms"

/*

   EPSSchurResidualNorms - Computes the column norms of residual vectors

   OP*V(1:n,l:m) - V*T(1:m,l:m) were on entry, OP*V has been computed and

   stored in AV. ldt is the leading dimension of T. On exit, rsd(l) to

   rsd(m) contain the computed norms.

*/

static PetscErrorCode EPSSchurResidualNorms(EPS eps,Vec *V,Vec *AV,PetscScalar *T,int l,int m,int ldt,PetscReal *rsd)

{

  PetscErrorCode ierr;

  int            i;

#if defined(PETSC_USE_COMPLEX)

  PetscScalar    t;

#endif

  PetscFunctionBegin;

  for (i=l;i<m;i++) {

    ierr = VecSet(eps->work[0],0.0);CHKERRQ(ierr);

    ierr = VecMAXPY(eps->work[0],m,T+ldt*i,V);CHKERRQ(ierr);

    ierr = VecWAXPY(eps->work[1],-1.0,eps->work[0],AV[i]);CHKERRQ(ierr);

#if !defined(PETSC_USE_COMPLEX)

    ierr = VecDot(eps->work[1],eps->work[1],rsd+i);CHKERRQ(ierr);

#else

    ierr = VecDot(eps->work[1],eps->work[1],&t);CHKERRQ(ierr);

    rsd[i] = PetscRealPart(t);

#endif    

  }

  for (i=l;i<m;i++) {

    if (i == m-1) {

      rsd[i] = sqrt(rsd[i]);  

    } else if (T[i+1+(ldt*i)]==0.0) {

      rsd[i] = sqrt(rsd[i]);

    } else {

      rsd[i] = sqrt(rsd[i]+rsd[i+1])/2.0;

      rsd[i+1] = rsd[i];

      i++;

    }

  }

  PetscFunctionReturn(0);

}

#undef __FUNCT__  

#define __FUNCT__ "EPSSolve_SUBSPACE"

PetscErrorCode EPSSolve_SUBSPACE(EPS eps)

{

  PetscErrorCode ierr;

  int            i,ngrp,nogrp,*itrsd,*itrsdold,

                 nxtsrr,idsrr,idort,nxtort,ncv = eps->ncv,its;

  PetscScalar    *T=eps->T,*U;

  PetscReal      arsd,oarsd,ctr,octr,ae,oae,*rsd,*rsdold,norm,tcond;

  PetscTruth     breakdown;

  /* Parameters */

  int            init = 5;        /* Number of initial iterations */

  PetscReal      stpfac = 1.5,    /* Max num of iter before next SRR step */

                 alpha = 1.0,     /* Used to predict convergence of next residual */

                 beta = 1.1,      /* Used to predict convergence of next residual */

                 grptol = 1e-8,   /* Tolerance for EPSFindGroup */

                 cnvtol = 1e-6;   /* Convergence criterion for cnv */

  int            orttol = 2;      /* Number of decimal digits whose loss

                                     can be tolerated in orthogonalization */

  PetscFunctionBegin;

  its = 0;

  ierr = PetscMalloc(sizeof(PetscScalar)*ncv*ncv,&U);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(PetscReal)*ncv,&rsd);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(PetscReal)*ncv,&rsdold);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(int)*ncv,&itrsd);CHKERRQ(ierr);

  ierr = PetscMalloc(sizeof(int)*ncv,&itrsdold);CHKERRQ(ierr);

  /* Generate set of initial vectors and orthonormalize them.

     Use initial vectors provided by the user if available   */

  for (i=0;i<ncv;i++) {

    if (i<eps->niv) { ierr = VecCopy(eps->IV[i],eps->V[i]);CHKERRQ(ierr); }

    else { ierr = SlepcVecSetRandom(eps->V[i]);CHKERRQ(ierr); }

    rsd[i] = 0.0;

    itrsd[i] = -1;

  }

  ierr = IPQRDecomposition(eps->ip,eps->V,0,ncv,PETSC_NULL,0,eps->work[0]);CHKERRQ(ierr);

  while (eps->its<eps->max_it) {

    eps->its++;

    /* Find group in previously computed eigenvalues */

    ierr = EPSFindGroup(eps->nconv,ncv,eps->eigr,eps->eigi,rsd,grptol,&nogrp,&octr,&oae,&oarsd);CHKERRQ(ierr);

    /* Compute a Rayleigh-Ritz projection step

       on the active columns (idx) */

    /* 1. AV(:,idx) = OP * V(:,idx) */

    for (i=eps->nconv;i<ncv;i++) {

      ierr = STApply(eps->OP,eps->V[i],eps->AV[i]);CHKERRQ(ierr);

    }

    /* 2. T(:,idx) = V' * AV(:,idx) */

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecMDot(eps->AV[i],ncv,eps->V,T+i*ncv);CHKERRQ(ierr);

    }

    /* 3. Reduce projected matrix to Hessenberg form: [U,T] = hess(T) */

    ierr = EPSDenseHessenberg(ncv,eps->nconv,T,ncv,U);CHKERRQ(ierr);

    /* 4. Reduce T to quasi-triangular (Schur) form */

    ierr = EPSDenseSchur(ncv,eps->nconv,T,ncv,U,eps->eigr,eps->eigi);CHKERRQ(ierr);

    /* 5. Sort diagonal elements in T and accumulate rotations on U */

    ierr = EPSSortDenseSchur(ncv,eps->nconv,T,ncv,U,eps->eigr,eps->eigi,eps->which);CHKERRQ(ierr);

    /* 6. AV(:,idx) = AV * U(:,idx) */

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecSet(eps->work[i],0.0);CHKERRQ(ierr);

      ierr = VecMAXPY(eps->work[i],ncv,U+ncv*i,eps->AV);CHKERRQ(ierr);

    }    

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecCopy(eps->work[i],eps->AV[i]);CHKERRQ(ierr);

    }    

    /* 7. V(:,idx) = V * U(:,idx) */

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecSet(eps->work[i],0.0);CHKERRQ(ierr);

      ierr = VecMAXPY(eps->work[i],ncv,U+ncv*i,eps->V);CHKERRQ(ierr);

    }    

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecCopy(eps->work[i],eps->V[i]);CHKERRQ(ierr);

    }    

    /* Compute residuals */

    for (i=0;i<ncv;i++) { rsdold[i] = rsd[i]; }

    ierr = EPSSchurResidualNorms(eps,eps->V,eps->AV,T,eps->nconv,ncv,ncv,rsd);CHKERRQ(ierr);

    for (i=0;i<ncv;i++) {

      eps->errest[i] = rsd[i] / SlepcAbsEigenvalue(eps->eigr[i],eps->eigi[i]);

    }

    EPSMonitor(eps,eps->its,eps->nconv,eps->eigr,eps->eigi,eps->errest,ncv);

    /* Convergence check */

    for (i=0;i<ncv;i++) { itrsdold[i] = itrsd[i]; }

    for (i=eps->nconv;i<ncv;i++) { itrsd[i] = its; }

    for (;;) {

      /* Find group in currently computed eigenvalues */

      ierr = EPSFindGroup(eps->nconv,ncv,eps->eigr,eps->eigi,rsd,grptol,&ngrp,&ctr,&ae,&arsd);CHKERRQ(ierr);

      if (ngrp!=nogrp) break;

      if (ngrp==0) break;

      if (PetscAbsScalar(ae-oae)>ctr*cnvtol*(itrsd[eps->nconv]-itrsdold[eps->nconv])) break;

      if (arsd>ctr*eps->tol) break;

      eps->nconv = eps->nconv + ngrp;

      if (eps->nconv>=ncv) break;

    }

    if (eps->nconv>=eps->nev) break;

    /* Compute nxtsrr (iteration of next projection step) */

    nxtsrr = PetscMin(eps->max_it,PetscMax((int)floor(stpfac*its), init));

    if (ngrp!=nogrp || ngrp==0 || arsd>=oarsd) {

      idsrr = nxtsrr - its;

    } else {

      idsrr = (int)floor(alpha+beta*(itrsdold[eps->nconv]-itrsd[eps->nconv])*log(arsd/eps->tol)/log(arsd/oarsd));

      idsrr = PetscMax(1,idsrr);

    }

    nxtsrr = PetscMin(nxtsrr,its+idsrr);

    /* Compute nxtort (iteration of next orthogonalization step) */

    ierr = PetscMemcpy(U,T,sizeof(PetscScalar)*ncv);CHKERRQ(ierr);

    ierr = EPSHessCond(U,ncv,&tcond);CHKERRQ(ierr);

    idort = PetscMax(1,(int)floor(orttol/PetscMax(1,log10(tcond))));    

    nxtort = PetscMin(its+idort, nxtsrr);

    /* V(:,idx) = AV(:,idx) */

    for (i=eps->nconv;i<ncv;i++) {

      ierr = VecCopy(eps->AV[i],eps->V[i]);CHKERRQ(ierr);

    }

    its++;

    /* Orthogonalization loop */

    do {

      while (its<nxtort) {

        /* AV(:,idx) = OP * V(:,idx) */

        for (i=eps->nconv;i<ncv;i++) {

          ierr = STApply(eps->OP,eps->V[i],eps->AV[i]);CHKERRQ(ierr);

        }

        /* V(:,idx) = AV(:,idx) with normalization */

        for (i=eps->nconv;i<ncv;i++) {

          ierr = VecCopy(eps->AV[i],eps->V[i]);CHKERRQ(ierr);

          ierr = VecNorm(eps->V[i],NORM_INFINITY,&norm);CHKERRQ(ierr);

          ierr = VecScale(eps->V[i],1/norm);CHKERRQ(ierr);

        }

        its++;

      }

      /* Orthonormalize vectors */

      for (i=eps->nconv;i<ncv;i++) {

        ierr = IPOrthogonalize(eps->ip,i+eps->nds,PETSC_NULL,eps->DSV,eps->V[i],PETSC_NULL,&norm,&breakdown,eps->work[0]);CHKERRQ(ierr);

        if (breakdown) {

          ierr = SlepcVecSetRandom(eps->V[i]);CHKERRQ(ierr);

          ierr = IPOrthogonalize(eps->ip,i+eps->nds,PETSC_NULL,eps->DSV,eps->V[i],PETSC_NULL,&norm,&breakdown,eps->work[0]);CHKERRQ(ierr);

        }

        ierr = VecScale(eps->V[i],1/norm);CHKERRQ(ierr);

      }

      nxtort = PetscMin(its+idort,nxtsrr);

    } while (its<nxtsrr);

  }

  ierr = PetscFree(U);CHKERRQ(ierr);

  ierr = PetscFree(rsd);CHKERRQ(ierr);

  ierr = PetscFree(rsdold);CHKERRQ(ierr);

  ierr = PetscFree(itrsd);CHKERRQ(ierr);

  ierr = PetscFree(itrsdold);CHKERRQ(ierr);

  if( eps->nconv == eps->nev ) eps->reason = EPS_CONVERGED_TOL;

  else eps->reason = EPS_DIVERGED_ITS;

  PetscFunctionReturn(0);

}

EXTERN_C_BEGIN

#undef __FUNCT__  

#define __FUNCT__ "EPSCreate_SUBSPACE"

PetscErrorCode EPSCreate_SUBSPACE(EPS eps)

{

  PetscFunctionBegin;

  eps->ops->solve                = EPSSolve_SUBSPACE;

  eps->ops->setup                = EPSSetUp_SUBSPACE;

  eps->ops->destroy              = EPSDestroy_Default;

  eps->ops->backtransform        = EPSBackTransform_Default;

  eps->ops->computevectors       = EPSComputeVectors_Schur;

  PetscFunctionReturn(0);

}

EXTERN_C_END