hetrf(3)

NAME
hetrf - {he,sy}trf: triangular factor

SYNOPSIS

  Functions

subroutine chetrf (uplo, n, a, lda, ipiv, work, lwork, info)
CHETRF
subroutine csytrf (uplo, n, a, lda, ipiv, work, lwork, info)
CSYTRF
subroutine dsytrf (uplo, n, a, lda, ipiv, work, lwork, info)
DSYTRF
subroutine ssytrf (uplo, n, a, lda, ipiv, work, lwork, info)
SSYTRF
subroutine zhetrf (uplo, n, a, lda, ipiv, work, lwork, info)
ZHETRF
subroutine zsytrf (uplo, n, a, lda, ipiv, work, lwork, info)
ZSYTRF

Detailed Description

Function Documentation

  subroutine chetrf (character uplo, integer n, complex, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, complex, dimension( * ) work, integer lwork, integer info)

CHETRF

Purpose:

    !>
    !> CHETRF computes the factorization of a complex Hermitian matrix A
    !> using the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U*D*U**H  or  A = L*D*L**H
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is Hermitian and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is COMPLEX array, dimension (LDA,N)
    !>          On entry, the Hermitian matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is COMPLEX array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK. LWORK >= 1. For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U*D*U**H, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**H, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

  subroutine csytrf (character uplo, integer n, complex, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, complex, dimension( * ) work, integer lwork, integer info)

CSYTRF

Purpose:

    !>
    !> CSYTRF computes the factorization of a complex symmetric matrix A
    !> using the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U*D*U**T  or  A = L*D*L**T
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is symmetric and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is COMPLEX array, dimension (LDA,N)
    !>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is COMPLEX array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK.  LWORK >=1.  For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>
    !>          If LWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal size of the WORK array, returns
    !>          this value as the first entry of the WORK array, and no error
    !>          message related to LWORK is issued by XERBLA.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U*D*U**T, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**T, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

  subroutine dsytrf (character uplo, integer n, double precision, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, double precision, dimension( * ) work, integer lwork, integer info)

DSYTRF

Purpose:

    !>
    !> DSYTRF computes the factorization of a real symmetric matrix A using
    !> the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U**T*D*U  or  A = L*D*L**T
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is symmetric and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is DOUBLE PRECISION array, dimension (LDA,N)
    !>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK.  LWORK >= 1.  For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>
    !>          If LWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal size of the WORK array, returns
    !>          this value as the first entry of the WORK array, and no error
    !>          message related to LWORK is issued by XERBLA.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U**T*D*U, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**T, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

  subroutine ssytrf (character uplo, integer n, real, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, real, dimension( * ) work, integer lwork, integer info)

SSYTRF

Purpose:

    !>
    !> SSYTRF computes the factorization of a real symmetric matrix A using
    !> the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U**T*D*U  or  A = L*D*L**T
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is symmetric and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is REAL array, dimension (LDA,N)
    !>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is REAL array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK.  LWORK >=1.  For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>
    !>          If LWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal size of the WORK array, returns
    !>          this value as the first entry of the WORK array, and no error
    !>          message related to LWORK is issued by XERBLA.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U**T*D*U, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**T, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

  subroutine zhetrf (character uplo, integer n, complex*16, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, complex*16, dimension( * ) work, integer lwork, integer info)

ZHETRF

Purpose:

    !>
    !> ZHETRF computes the factorization of a complex Hermitian matrix A
    !> using the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U*D*U**H  or  A = L*D*L**H
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is Hermitian and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is COMPLEX*16 array, dimension (LDA,N)
    !>          On entry, the Hermitian matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK. LWORK >= 1. For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U*D*U**H, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**H, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

  subroutine zsytrf (character uplo, integer n, complex*16, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, complex*16, dimension( * ) work, integer lwork, integer info)

ZSYTRF

Purpose:

    !>
    !> ZSYTRF computes the factorization of a complex symmetric matrix A
    !> using the Bunch-Kaufman diagonal pivoting method.  The form of the
    !> factorization is
    !>
    !>    A = U*D*U**T  or  A = L*D*L**T
    !>
    !> where U (or L) is a product of permutation and unit upper (lower)
    !> triangular matrices, and D is symmetric and block diagonal with
    !> 1-by-1 and 2-by-2 diagonal blocks.
    !>
    !> This is the blocked version of the algorithm, calling Level 3 BLAS.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    A

    !>          A is COMPLEX*16 array, dimension (LDA,N)
    !>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
    !>          N-by-N upper triangular part of A contains the upper
    !>          triangular part of the matrix A, and the strictly lower
    !>          triangular part of A is not referenced.  If UPLO = 'L', the
    !>          leading N-by-N lower triangular part of A contains the lower
    !>          triangular part of the matrix A, and the strictly upper
    !>          triangular part of A is not referenced.
    !>
    !>          On exit, the block diagonal matrix D and the multipliers used
    !>          to obtain the factor U or L (see below for further details).
    !>

    LDA

    !>          LDA is INTEGER
    !>          The leading dimension of the array A.  LDA >= max(1,N).
    !>

    IPIV

    !>          IPIV is INTEGER array, dimension (N)
    !>          Details of the interchanges and the block structure of D.
    !>          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
    !>          interchanged and D(k,k) is a 1-by-1 diagonal block.
    !>          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
    !>          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
    !>          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
    !>          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
    !>          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
    !>

    WORK

    !>          WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
    !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
    !>

    LWORK

    !>          LWORK is INTEGER
    !>          The length of WORK.  LWORK >=1.  For best performance
    !>          LWORK >= N*NB, where NB is the block size returned by ILAENV.
    !>
    !>          If LWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal size of the WORK array, returns
    !>          this value as the first entry of the WORK array, and no error
    !>          message related to LWORK is issued by XERBLA.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
    !>                has been completed, but the block diagonal matrix D is
    !>                exactly singular, and division by zero will occur if it
    !>                is used to solve a system of equations.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  If UPLO = 'U', then A = U*D*U**T, where
    !>     U = P(n)*U(n)* ... *P(k)U(k)* ...,
    !>  i.e., U is a product of terms P(k)*U(k), where k decreases from n to
    !>  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    v    0   )   k-s
    !>     U(k) =  (   0    I    0   )   s
    !>             (   0    0    I   )   n-k
    !>                k-s   s   n-k
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
    !>  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
    !>  and A(k,k), and v overwrites A(1:k-2,k-1:k).
    !>
    !>  If UPLO = 'L', then A = L*D*L**T, where
    !>     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
    !>  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
    !>  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
    !>  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
    !>  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
    !>  that if the diagonal block D(k) is of order s (s = 1 or 2), then
    !>
    !>             (   I    0     0   )  k-1
    !>     L(k) =  (   0    I     0   )  s
    !>             (   0    v     I   )  n-k-s+1
    !>                k-1   s  n-k-s+1
    !>
    !>  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
    !>  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
    !>  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
    !>

Author

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