SLATEC Routines --- DSYR2 ---


    Note: this is a BLAS routine and is not in libslatec.a

*DECK DSYR2
      SUBROUTINE DSYR2 (UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA)
C***BEGIN PROLOGUE  DSYR2
C***PURPOSE  Perform the symmetric rank 2 operation.
C***LIBRARY   SLATEC (BLAS)
C***CATEGORY  D1B4
C***TYPE      DOUBLE PRECISION (SSYR2-S, DSYR2-D, CSYR2-C)
C***KEYWORDS  LEVEL 2 BLAS, LINEAR ALGEBRA
C***AUTHOR  Dongarra, J. J., (ANL)
C           Du Croz, J., (NAG)
C           Hammarling, S., (NAG)
C           Hanson, R. J., (SNLA)
C***DESCRIPTION
C
C  DSYR2  performs the symmetric rank 2 operation
C
C     A := alpha*x*y' + alpha*y*x' + A,
C
C  where alpha is a scalar, x and y are n element vectors and A is an n
C  by n symmetric matrix.
C
C  Parameters
C  ==========
C
C  UPLO   - CHARACTER*1.
C           On entry, UPLO specifies whether the upper or lower
C           triangular part of the array A is to be referenced as
C           follows:
C
C              UPLO = 'U' or 'u'   Only the upper triangular part of A
C                                  is to be referenced.
C
C              UPLO = 'L' or 'l'   Only the lower triangular part of A
C                                  is to be referenced.
C
C           Unchanged on exit.
C
C  N      - INTEGER.
C           On entry, N specifies the order of the matrix A.
C           N must be at least zero.
C           Unchanged on exit.
C
C  ALPHA  - DOUBLE PRECISION.
C           On entry, ALPHA specifies the scalar alpha.
C           Unchanged on exit.
C
C  X      - DOUBLE PRECISION array of dimension at least
C           ( 1 + ( n - 1)*abs( INCX)).
C           Before entry, the incremented array X must contain the n
C           element vector x.
C           Unchanged on exit.
C
C  INCX   - INTEGER.
C           On entry, INCX specifies the increment for the elements of
C           X. INCX must not be zero.
C           Unchanged on exit.
C
C  Y      - DOUBLE PRECISION array of dimension at least
C           ( 1 + ( n - 1 )*abs( INCY ) ).
C           Before entry, the incremented array Y must contain the n
C           element vector y.
C           Unchanged on exit.
C
C  INCY   - INTEGER.
C           On entry, INCY specifies the increment for the elements of
C           Y. INCY must not be zero.
C           Unchanged on exit.
C
C  A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
C           Before entry with  UPLO = 'U' or 'u', the leading n by n
C           upper triangular part of the array A must contain the upper
C           triangular part of the symmetric matrix and the strictly
C           lower triangular part of A is not referenced. On exit, the
C           upper triangular part of the array A is overwritten by the
C           upper triangular part of the updated matrix.
C           Before entry with UPLO = 'L' or 'l', the leading n by n
C           lower triangular part of the array A must contain the lower
C           triangular part of the symmetric matrix and the strictly
C           upper triangular part of A is not referenced. On exit, the
C           lower triangular part of the array A is overwritten by the
C           lower triangular part of the updated matrix.
C
C  LDA    - INTEGER.
C           On entry, LDA specifies the first dimension of A as declared
C           in the calling (sub) program. LDA must be at least
C           max( 1, n ).
C           Unchanged on exit.
C
C***REFERENCES  Dongarra, J. J., Du Croz, J., Hammarling, S., and
C                 Hanson, R. J.  An extended set of Fortran basic linear
C                 algebra subprograms.  ACM TOMS, Vol. 14, No. 1,
C                 pp. 1-17, March 1988.
C***ROUTINES CALLED  LSAME, XERBLA
C***REVISION HISTORY  (YYMMDD)
C   861022  DATE WRITTEN
C   910605  Modified to meet SLATEC prologue standards.  Only comment
C           lines were modified.  (BKS)
C***END PROLOGUE  DSYR2