*DECK SSPR
SUBROUTINE SSPR (UPLO, N, ALPHA, X, INCX, AP)
C***BEGIN PROLOGUE SSPR
C***PURPOSE Performs the symmetric rank 1 operation.
C***LIBRARY SLATEC (BLAS)
C***CATEGORY D1B4
C***TYPE SINGLE PRECISION (SSPR-S)
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 SSPR performs the symmetric rank 1 operation
C
C A := alpha*x*x' + A,
C
C where alpha is a real scalar, x is an n element vector and A is an
C n by n symmetric matrix, supplied in packed form.
C
C Parameters
C ==========
C
C UPLO - CHARACTER*1.
C On entry, UPLO specifies whether the upper or lower
C triangular part of the matrix A is supplied in the packed
C array AP as follows:
C
C UPLO = 'U' or 'u' The upper triangular part of A is
C supplied in AP.
C
C UPLO = 'L' or 'l' The lower triangular part of A is
C supplied in AP.
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 - REAL .
C On entry, ALPHA specifies the scalar alpha.
C Unchanged on exit.
C
C X - REAL 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 AP - REAL array of DIMENSION at least
C ( ( n*( n + 1 ) )/2 ).
C Before entry with UPLO = 'U' or 'u', the array AP must
C contain the upper triangular part of the symmetric matrix
C packed sequentially, column by column, so that AP( 1 )
C contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )
C and a( 2, 2 ) respectively, and so on. On exit, the array
C AP is overwritten by the upper triangular part of the
C updated matrix.
C Before entry with UPLO = 'L' or 'l', the array AP must
C contain the lower triangular part of the symmetric matrix
C packed sequentially, column by column, so that AP( 1 )
C contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )
C and a( 3, 1 ) respectively, and so on. On exit, the array
C AP is overwritten by the lower triangular part of the
C updated matrix.
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 SSPR
C .. Scalar Arguments ..
REAL ALPHA
INTEGER INCX, N
CHARACTER*1 UPLO
C .. Array Arguments ..
REAL AP( * ), X( * )
C .. Parameters ..
REAL ZERO
PARAMETER ( ZERO = 0.0E+0 )
C .. Local Scalars ..
REAL TEMP
INTEGER I, INFO, IX, J, JX, K, KK, KX
C .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
C .. External Subroutines ..
EXTERNAL XERBLA
C***FIRST EXECUTABLE STATEMENT SSPR
C
C Test the input parameters.
C
INFO = 0
IF ( .NOT.LSAME( UPLO, 'U' ).AND.
$ .NOT.LSAME( UPLO, 'L' ) )THEN
INFO = 1
ELSE IF( N.LT.0 )THEN
INFO = 2
ELSE IF( INCX.EQ.0 )THEN
INFO = 5
END IF
IF( INFO.NE.0 )THEN
CALL XERBLA( 'SSPR ', INFO )
RETURN
END IF
C
C Quick return if possible.
C
IF( ( N.EQ.0 ).OR.( ALPHA.EQ.ZERO ) )
$ RETURN
C
C Set the start point in X if the increment is not unity.
C
IF( INCX.LE.0 )THEN
KX = 1 - ( N - 1 )*INCX
ELSE IF( INCX.NE.1 )THEN
KX = 1
END IF
C
C Start the operations. In this version the elements of the array AP
C are accessed sequentially with one pass through AP.
C
KK = 1
IF( LSAME( UPLO, 'U' ) )THEN
C
C Form A when upper triangle is stored in AP.
C
IF( INCX.EQ.1 )THEN
DO 20, J = 1, N
IF( X( J ).NE.ZERO )THEN
TEMP = ALPHA*X( J )
K = KK
DO 10, I = 1, J
AP( K ) = AP( K ) + X( I )*TEMP
K = K + 1
10 CONTINUE
END IF
KK = KK + J
20 CONTINUE
ELSE
JX = KX
DO 40, J = 1, N
IF( X( JX ).NE.ZERO )THEN
TEMP = ALPHA*X( JX )
IX = KX
DO 30, K = KK, KK + J - 1
AP( K ) = AP( K ) + X( IX )*TEMP
IX = IX + INCX
30 CONTINUE
END IF
JX = JX + INCX
KK = KK + J
40 CONTINUE
END IF
ELSE
C
C Form A when lower triangle is stored in AP.
C
IF( INCX.EQ.1 )THEN
DO 60, J = 1, N
IF( X( J ).NE.ZERO )THEN
TEMP = ALPHA*X( J )
K = KK
DO 50, I = J, N
AP( K ) = AP( K ) + X( I )*TEMP
K = K + 1
50 CONTINUE
END IF
KK = KK + N - J + 1
60 CONTINUE
ELSE
JX = KX
DO 80, J = 1, N
IF( X( JX ).NE.ZERO )THEN
TEMP = ALPHA*X( JX )
IX = JX
DO 70, K = KK, KK + N - J
AP( K ) = AP( K ) + X( IX )*TEMP
IX = IX + INCX
70 CONTINUE
END IF
JX = JX + INCX
KK = KK + N - J + 1
80 CONTINUE
END IF
END IF
C
RETURN
C
C End of SSPR .
C
END