!-----------------------------------------------------------------------------!
!   CP2K: A general program to perform molecular dynamics simulations         !
!   Copyright (C) 2000 - 2014  CP2K developers group                          !
!-----------------------------------------------------------------------------!

! *****************************************************************************
!> \brief Provides interfaces to LAPACK eigenvalue/SVD routines
!> \note
!>      We are using LAPACK interfaces, so please make sure in IBM/AIX you have
!>      the lapack library before essl: "xlf90 ... -llapack -lessl" !!!
!> \par History
!>      JGH (26-5-2001): delay D/S C/Z problem to the lapack library call
!> \author APSI
! *****************************************************************************
MODULE eigenvalueproblems

  
  USE kinds,                           ONLY: dp
  USE lapack,                          ONLY: lapack_cgesvd,&
                                             lapack_chpev,&
                                             lapack_sgesvd,&
                                             lapack_ssyev
  USE termination,                     ONLY: stop_program
#include "cp_common_uses.f90"

  IMPLICIT NONE

  PRIVATE

  PUBLIC :: diagonalise

  CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'eigenvalueproblems'

  INTERFACE diagonalise
     MODULE PROCEDURE diagonalise_ssyev
     MODULE PROCEDURE diagonalise_chpev
  END INTERFACE

  INTERFACE singular_values
     MODULE PROCEDURE cp2k_sgesvd
     MODULE PROCEDURE cp2k_cgesvd
  END INTERFACE

CONTAINS

! *****************************************************************************
!> \brief ...
!> \param matrix ...
!> \param mysize ...
!> \param storageform ...
!> \param eigenvalues ...
!> \param eigenvectors ...
! *****************************************************************************
SUBROUTINE diagonalise_ssyev( matrix, mysize, storageform, eigenvalues, &
                              eigenvectors )

    REAL(KIND=dp), INTENT(IN)                :: matrix( :, : )
    INTEGER, INTENT(IN)                      :: mysize
    CHARACTER(LEN=*), INTENT(IN)             :: storageform
    REAL(KIND=dp), INTENT(OUT)               :: eigenvalues( : ), &
                                                eigenvectors( :, : )

    CHARACTER(len=*), PARAMETER :: routineN = 'diagonalise_ssyev', &
      routineP = moduleN//':'//routineN
    CHARACTER, PARAMETER                     :: jobz = "V"

    CHARACTER                                :: uplo
    INTEGER                                  :: info, lda, lwork
    REAL(KIND=dp)                            :: work( 3 * mysize - 1 )

  IF ( storageform ( 1:5 ) == "Lower" .OR. &
       storageform ( 1:5 ) == "LOWER" .OR. &
       storageform ( 1:5 ) == "lower" ) THEN
     uplo = "L"
  ELSE IF ( storageform ( 1:5 ) == "Upper" .OR. &
       storageform ( 1:5 ) == "upper" .OR. &
       storageform ( 1:5 ) == "UPPER" ) THEN
     uplo = "U"
  ELSE
     CALL stop_program(routineN,moduleN,__LINE__,"Unknown form of storage")
  END IF

  lda = SIZE ( matrix, 1 )
  lwork = 3 * mysize - 1

  eigenvectors = matrix

  CALL lapack_ssyev ( jobz, uplo, mysize, eigenvectors, lda, eigenvalues, &
       work, lwork, info )
  IF ( info /= 0 ) THEN
     CALL stop_program(routineN,moduleN,__LINE__,"Error in diagonalisation")
  END IF

END SUBROUTINE diagonalise_ssyev

! *****************************************************************************
!> \brief ...
!> \param matrix ...
!> \param mysize ...
!> \param storageform ...
!> \param eigenvalues ...
!> \param eigenvectors ...
! *****************************************************************************
SUBROUTINE diagonalise_chpev ( matrix, mysize, storageform, eigenvalues, &
                               eigenvectors )

    COMPLEX(KIND=dp), INTENT(INOUT)          :: matrix( : )
    INTEGER, INTENT(IN)                      :: mysize
    CHARACTER(LEN=*), INTENT(IN)             :: storageform
    REAL(KIND=dp), INTENT(OUT)               :: eigenvalues( : )
    COMPLEX(KIND=dp), INTENT(OUT)            :: eigenvectors( :, : )

    CHARACTER(len=*), PARAMETER :: routineN = 'diagonalise_chpev', &
      routineP = moduleN//':'//routineN
    CHARACTER, PARAMETER                     :: jobz = "V"

    CHARACTER                                :: uplo
    INTEGER                                  :: info
    COMPLEX(KIND=dp)                         :: work( 2 * mysize - 1 )
    REAL(KIND=dp)                            :: rwork( 3 * mysize - 2 )

  IF ( storageform ( 1:5 ) == "Lower" .OR. &
       storageform ( 1:5 ) == "LOWER" .OR. &
       storageform ( 1:5 ) == "lower" ) THEN
     uplo = "L"
  ELSE IF ( storageform ( 1:5 ) == "Upper" .OR. &
       storageform ( 1:5 ) == "upper" .OR. &
       storageform ( 1:5 ) == "UPPER" ) THEN
     uplo = "U"
  ELSE
     CALL stop_program(routineN,moduleN,__LINE__,"Unknown form of storage")
  END IF

  CALL lapack_chpev ( jobz, uplo, mysize, matrix, eigenvalues, &
       eigenvectors, mysize, work, rwork, info )
  IF ( info /= 0 ) THEN
     CALL stop_program(routineN,moduleN,__LINE__,"Error in diagonalisation")
  END IF

END SUBROUTINE diagonalise_chpev

! *****************************************************************************
!> \brief ...
!> \param matrix ...
!> \param svalues ...
!> \param mrow ...
!> \param ncol ...
!> \param uvec ...
!> \param vtvec ...
! *****************************************************************************
SUBROUTINE cp2k_sgesvd ( matrix, svalues, mrow, ncol, uvec, vtvec )

    REAL(KIND=dp), INTENT(IN)                :: matrix( :, : )
    REAL(KIND=dp), INTENT(OUT)               :: svalues( : )
    INTEGER, INTENT(IN)                      :: mrow, ncol
    REAL(KIND=dp), INTENT(OUT)               :: uvec( :, : ), vtvec( :, : )

    CHARACTER(len=*), PARAMETER :: routineN = 'cp2k_sgesvd', &
      routineP = moduleN//':'//routineN
    CHARACTER, PARAMETER                     :: jobu = "A", jobvt = "A"

    INTEGER                                  :: info, lda, ldu, ldvt, lwork
    REAL(KIND=dp)                            :: work( 25 * ( mrow + ncol ) )

  lwork = 25 * ( mrow + ncol )
  lda = SIZE ( matrix, 1 )
  ldu = SIZE ( uvec, 1 )
  ldvt = SIZE ( vtvec, 1 )

  CALL lapack_sgesvd( jobu, jobvt, mrow, ncol, matrix, lda, svalues, &
        uvec, ldu, vtvec, ldvt, work, lwork, info )
  IF ( info /= 0 ) THEN
     CALL stop_program(routineN,moduleN,__LINE__,&
                       "Error in singular value decomposition.")
  END IF

END SUBROUTINE cp2k_sgesvd

! *****************************************************************************
!> \brief ...
!> \param matrix ...
!> \param svalues ...
!> \param mrow ...
!> \param ncol ...
!> \param uvec ...
!> \param vtvec ...
! *****************************************************************************
SUBROUTINE cp2k_cgesvd ( matrix, svalues, mrow, ncol, uvec, vtvec )

    COMPLEX(KIND=dp), INTENT(IN)             :: matrix( :, : )
    REAL(KIND=dp), INTENT(OUT)               :: svalues( : )
    INTEGER, INTENT(IN)                      :: mrow, ncol
    COMPLEX(KIND=dp), INTENT(OUT)            :: uvec( :, : ), vtvec( :, : )

    CHARACTER(len=*), PARAMETER :: routineN = 'cp2k_cgesvd', &
      routineP = moduleN//':'//routineN
    CHARACTER, PARAMETER                     :: jobu = "A", jobvt = "A"

    INTEGER                                  :: info, lda, ldu, ldvt, lwork
    COMPLEX(KIND=dp)                         :: work( 25 * ( mrow + ncol ) )
    REAL(KIND=dp)                            :: rwork( 25 * ( mrow + ncol ) )

  lwork = 25 * ( mrow + ncol )
  lda = SIZE ( matrix, 1 )
  ldu = SIZE ( uvec, 1 )
  ldvt = SIZE ( vtvec, 1 )

  CALL lapack_cgesvd( jobu, jobvt, mrow, ncol, matrix, lda, svalues, &
        uvec, ldu, vtvec, ldvt, work, lwork, rwork, info )
  IF ( info /= 0 ) THEN
     CALL stop_program(routineN,moduleN,__LINE__,&
                       "Error in singular value decomposition.")
  END IF

END SUBROUTINE cp2k_cgesvd

END MODULE eigenvalueproblems

