Provided by: liblapack-doc_3.12.0-3build1_all bug

NAME

       her2k - {he,sy}r2k: Hermitian/symmetric rank-2k update

SYNOPSIS

   Functions
       subroutine cher2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           CHER2K
       subroutine csyr2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           CSYR2K
       subroutine dsyr2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           DSYR2K
       subroutine ssyr2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           SSYR2K
       subroutine zher2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           ZHER2K
       subroutine zsyr2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc)
           ZSYR2K

Detailed Description

Function Documentation

   subroutine cher2k (character uplo, character trans, integer n, integer k, complex alpha,
       complex, dimension(lda,*) a, integer lda, complex, dimension(ldb,*) b, integer ldb, real
       beta, complex, dimension(ldc,*) c, integer ldc)
       CHER2K

       Purpose:

            CHER2K  performs one of the hermitian rank 2k operations

               C := alpha*A*B**H + conjg( alpha )*B*A**H + beta*C,

            or

               C := alpha*A**H*B + conjg( alpha )*B**H*A + beta*C,

            where  alpha and beta  are scalars with  beta  real,  C is an  n by n
            hermitian matrix and  A and B  are  n by k matrices in the first case
            and  k by n  matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'    C := alpha*A*B**H          +
                                                    conjg( alpha )*B*A**H +
                                                    beta*C.

                         TRANS = 'C' or 'c'    C := alpha*A**H*B          +
                                                    conjg( alpha )*B**H*A +
                                                    beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'C' or 'c',  K  specifies  the number of rows of the
                      matrices  A and B.  K must be at least zero.

           ALPHA

                     ALPHA is COMPLEX
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is COMPLEX array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is COMPLEX array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).

           BETA

                     BETA is REAL
                      On entry, BETA specifies the scalar beta.

           C

                     C is COMPLEX array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  hermitian matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  hermitian matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.
                      Note that the imaginary parts of the diagonal elements need
                      not be set,  they are assumed to be zero,  and on exit they
                      are set to zero.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

             -- Modified 8-Nov-93 to set C(J,J) to REAL( C(J,J) ) when BETA = 1.
                Ed Anderson, Cray Research Inc.

   subroutine csyr2k (character uplo, character trans, integer n, integer k, complex alpha,
       complex, dimension(lda,*) a, integer lda, complex, dimension(ldb,*) b, integer ldb,
       complex beta, complex, dimension(ldc,*) c, integer ldc)
       CSYR2K

       Purpose:

            CSYR2K  performs one of the symmetric rank 2k operations

               C := alpha*A*B**T + alpha*B*A**T + beta*C,

            or

               C := alpha*A**T*B + alpha*B**T*A + beta*C,

            where  alpha and beta  are scalars,  C is an  n by n symmetric matrix
            and  A and B  are  n by k  matrices  in the  first  case  and  k by n
            matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'    C := alpha*A*B**T + alpha*B*A**T +
                                                    beta*C.

                         TRANS = 'T' or 't'    C := alpha*A**T*B + alpha*B**T*A +
                                                    beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'T' or 't',  K  specifies  the number of rows of the
                      matrices  A and B.  K must be at least zero.

           ALPHA

                     ALPHA is COMPLEX
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is COMPLEX array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is COMPLEX array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).

           BETA

                     BETA is COMPLEX
                      On entry, BETA specifies the scalar beta.

           C

                     C is COMPLEX array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  symmetric matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  symmetric matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

   subroutine dsyr2k (character uplo, character trans, integer n, integer k, double precision
       alpha, double precision, dimension(lda,*) a, integer lda, double precision,
       dimension(ldb,*) b, integer ldb, double precision beta, double precision, dimension(ldc,*)
       c, integer ldc)
       DSYR2K

       Purpose:

            DSYR2K  performs one of the symmetric rank 2k operations

               C := alpha*A*B**T + alpha*B*A**T + beta*C,

            or

               C := alpha*A**T*B + alpha*B**T*A + beta*C,

            where  alpha and beta  are scalars, C is an  n by n  symmetric matrix
            and  A and B  are  n by k  matrices  in the  first  case  and  k by n
            matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'   C := alpha*A*B**T + alpha*B*A**T +
                                                   beta*C.

                         TRANS = 'T' or 't'   C := alpha*A**T*B + alpha*B**T*A +
                                                   beta*C.

                         TRANS = 'C' or 'c'   C := alpha*A**T*B + alpha*B**T*A +
                                                   beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'T' or 't' or 'C' or 'c',  K  specifies  the  number
                      of rows of the matrices  A and B.  K must be at least  zero.

           ALPHA

                     ALPHA is DOUBLE PRECISION.
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is DOUBLE PRECISION array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is DOUBLE PRECISION array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).

           BETA

                     BETA is DOUBLE PRECISION.
                      On entry, BETA specifies the scalar beta.

           C

                     C is DOUBLE PRECISION array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  symmetric matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  symmetric matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

   subroutine ssyr2k (character uplo, character trans, integer n, integer k, real alpha, real,
       dimension(lda,*) a, integer lda, real, dimension(ldb,*) b, integer ldb, real beta, real,
       dimension(ldc,*) c, integer ldc)
       SSYR2K

       Purpose:

            SSYR2K  performs one of the symmetric rank 2k operations

               C := alpha*A*B**T + alpha*B*A**T + beta*C,

            or

               C := alpha*A**T*B + alpha*B**T*A + beta*C,

            where  alpha and beta  are scalars, C is an  n by n  symmetric matrix
            and  A and B  are  n by k  matrices  in the  first  case  and  k by n
            matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'   C := alpha*A*B**T + alpha*B*A**T +
                                                   beta*C.

                         TRANS = 'T' or 't'   C := alpha*A**T*B + alpha*B**T*A +
                                                   beta*C.

                         TRANS = 'C' or 'c'   C := alpha*A**T*B + alpha*B**T*A +
                                                   beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'T' or 't' or 'C' or 'c',  K  specifies  the  number
                      of rows of the matrices  A and B.  K must be at least  zero.

           ALPHA

                     ALPHA is REAL
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is REAL array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is REAL array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).

           BETA

                     BETA is REAL
                      On entry, BETA specifies the scalar beta.

           C

                     C is REAL array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  symmetric matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  symmetric matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

   subroutine zher2k (character uplo, character trans, integer n, integer k, complex*16 alpha,
       complex*16, dimension(lda,*) a, integer lda, complex*16, dimension(ldb,*) b, integer ldb,
       double precision beta, complex*16, dimension(ldc,*) c, integer ldc)
       ZHER2K

       Purpose:

            ZHER2K  performs one of the hermitian rank 2k operations

               C := alpha*A*B**H + conjg( alpha )*B*A**H + beta*C,

            or

               C := alpha*A**H*B + conjg( alpha )*B**H*A + beta*C,

            where  alpha and beta  are scalars with  beta  real,  C is an  n by n
            hermitian matrix and  A and B  are  n by k matrices in the first case
            and  k by n  matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'    C := alpha*A*B**H          +
                                                    conjg( alpha )*B*A**H +
                                                    beta*C.

                         TRANS = 'C' or 'c'    C := alpha*A**H*B          +
                                                    conjg( alpha )*B**H*A +
                                                    beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'C' or 'c',  K  specifies  the number of rows of the
                      matrices  A and B.  K must be at least zero.

           ALPHA

                     ALPHA is COMPLEX*16 .
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is COMPLEX*16 array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is COMPLEX*16 array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).
                      Unchanged on exit.

           BETA

                     BETA is DOUBLE PRECISION .
                      On entry, BETA specifies the scalar beta.

           C

                     C is COMPLEX*16 array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  hermitian matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  hermitian matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.
                      Note that the imaginary parts of the diagonal elements need
                      not be set,  they are assumed to be zero,  and on exit they
                      are set to zero.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

             -- Modified 8-Nov-93 to set C(J,J) to DBLE( C(J,J) ) when BETA = 1.
                Ed Anderson, Cray Research Inc.

   subroutine zsyr2k (character uplo, character trans, integer n, integer k, complex*16 alpha,
       complex*16, dimension(lda,*) a, integer lda, complex*16, dimension(ldb,*) b, integer ldb,
       complex*16 beta, complex*16, dimension(ldc,*) c, integer ldc)
       ZSYR2K

       Purpose:

            ZSYR2K  performs one of the symmetric rank 2k operations

               C := alpha*A*B**T + alpha*B*A**T + beta*C,

            or

               C := alpha*A**T*B + alpha*B**T*A + beta*C,

            where  alpha and beta  are scalars,  C is an  n by n symmetric matrix
            and  A and B  are  n by k  matrices  in the  first  case  and  k by n
            matrices in the second case.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                      On  entry,   UPLO  specifies  whether  the  upper  or  lower
                      triangular  part  of the  array  C  is to be  referenced  as
                      follows:

                         UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                             is to be referenced.

                         UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                             is to be referenced.

           TRANS

                     TRANS is CHARACTER*1
                      On entry,  TRANS  specifies the operation to be performed as
                      follows:

                         TRANS = 'N' or 'n'    C := alpha*A*B**T + alpha*B*A**T +
                                                    beta*C.

                         TRANS = 'T' or 't'    C := alpha*A**T*B + alpha*B**T*A +
                                                    beta*C.

           N

                     N is INTEGER
                      On entry,  N specifies the order of the matrix C.  N must be
                      at least zero.

           K

                     K is INTEGER
                      On entry with  TRANS = 'N' or 'n',  K  specifies  the number
                      of  columns  of the  matrices  A and B,  and on  entry  with
                      TRANS = 'T' or 't',  K  specifies  the number of rows of the
                      matrices  A and B.  K must be at least zero.

           ALPHA

                     ALPHA is COMPLEX*16
                      On entry, ALPHA specifies the scalar alpha.

           A

                     A is COMPLEX*16 array, dimension ( LDA, ka ), where ka is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  A  must contain the matrix  A,  otherwise
                      the leading  k by n  part of the array  A  must contain  the
                      matrix A.

           LDA

                     LDA is INTEGER
                      On entry, LDA specifies the first dimension of A as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDA must be at least  max( 1, n ), otherwise  LDA must
                      be at least  max( 1, k ).

           B

                     B is COMPLEX*16 array, dimension ( LDB, kb ), where kb is
                      k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
                      Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
                      part of the array  B  must contain the matrix  B,  otherwise
                      the leading  k by n  part of the array  B  must contain  the
                      matrix B.

           LDB

                     LDB is INTEGER
                      On entry, LDB specifies the first dimension of B as declared
                      in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
                      then  LDB must be at least  max( 1, n ), otherwise  LDB must
                      be at least  max( 1, k ).

           BETA

                     BETA is COMPLEX*16
                      On entry, BETA specifies the scalar beta.

           C

                     C is COMPLEX*16 array, dimension ( LDC, N )
                      Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
                      upper triangular part of the array C must contain the upper
                      triangular part  of the  symmetric matrix  and the strictly
                      lower triangular part of C is not referenced.  On exit, the
                      upper triangular part of the array  C is overwritten by the
                      upper triangular part of the updated matrix.
                      Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
                      lower triangular part of the array C must contain the lower
                      triangular part  of the  symmetric matrix  and the strictly
                      upper triangular part of C is not referenced.  On exit, the
                      lower triangular part of the array  C is overwritten by the
                      lower triangular part of the updated matrix.

           LDC

                     LDC is INTEGER
                      On entry, LDC specifies the first dimension of C as declared
                      in  the  calling  (sub)  program.   LDC  must  be  at  least
                      max( 1, n ).

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             Level 3 Blas routine.

             -- Written on 8-February-1989.
                Jack Dongarra, Argonne National Laboratory.
                Iain Duff, AERE Harwell.
                Jeremy Du Croz, Numerical Algorithms Group Ltd.
                Sven Hammarling, Numerical Algorithms Group Ltd.

Author

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