*DECK DSPR2 SUBROUTINE DSPR2 (UPLO, N, ALPHA, X, INCX, Y, INCY, AP) C***BEGIN PROLOGUE DSPR2 C***PURPOSE Perform the symmetric rank 2 operation. C***LIBRARY SLATEC (BLAS) C***CATEGORY D1B4 C***TYPE DOUBLE PRECISION (SSPR2-S, DSPR2-D, CSPR2-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 DSPR2 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 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 - 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 AP - DOUBLE PRECISION 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 DSPR2 C .. Scalar Arguments .. DOUBLE PRECISION ALPHA INTEGER INCX, INCY, N CHARACTER*1 UPLO C .. Array Arguments .. DOUBLE PRECISION AP( * ), X( * ), Y( * ) C .. Parameters .. DOUBLE PRECISION ZERO PARAMETER ( ZERO = 0.0D+0 ) C .. Local Scalars .. DOUBLE PRECISION TEMP1, TEMP2 INTEGER I, INFO, IX, IY, J, JX, JY, K, KK, KX, KY C .. External Functions .. LOGICAL LSAME EXTERNAL LSAME C .. External Subroutines .. EXTERNAL XERBLA C***FIRST EXECUTABLE STATEMENT DSPR2 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 ELSE IF( INCY.EQ.0 )THEN INFO = 7 END IF IF( INFO.NE.0 )THEN CALL XERBLA( 'DSPR2 ', INFO ) RETURN END IF C C Quick return if possible. C IF( ( N.EQ.0 ).OR.( ALPHA.EQ.ZERO ) ) $ RETURN C C Set up the start points in X and Y if the increments are not both C unity. C IF( ( INCX.NE.1 ).OR.( INCY.NE.1 ) )THEN IF( INCX.GT.0 )THEN KX = 1 ELSE KX = 1 - ( N - 1 )*INCX END IF IF( INCY.GT.0 )THEN KY = 1 ELSE KY = 1 - ( N - 1 )*INCY END IF JX = KX JY = KY 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 ).AND.( INCY.EQ.1 ) )THEN DO 20, J = 1, N IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN TEMP1 = ALPHA*Y( J ) TEMP2 = ALPHA*X( J ) K = KK DO 10, I = 1, J AP( K ) = AP( K ) + X( I )*TEMP1 + Y( I )*TEMP2 K = K + 1 10 CONTINUE END IF KK = KK + J 20 CONTINUE ELSE DO 40, J = 1, N IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN TEMP1 = ALPHA*Y( JY ) TEMP2 = ALPHA*X( JX ) IX = KX IY = KY DO 30, K = KK, KK + J - 1 AP( K ) = AP( K ) + X( IX )*TEMP1 + Y( IY )*TEMP2 IX = IX + INCX IY = IY + INCY 30 CONTINUE END IF JX = JX + INCX JY = JY + INCY KK = KK + J 40 CONTINUE END IF ELSE C C Form A when lower triangle is stored in AP. C IF( ( INCX.EQ.1 ).AND.( INCY.EQ.1 ) )THEN DO 60, J = 1, N IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN TEMP1 = ALPHA*Y( J ) TEMP2 = ALPHA*X( J ) K = KK DO 50, I = J, N AP( K ) = AP( K ) + X( I )*TEMP1 + Y( I )*TEMP2 K = K + 1 50 CONTINUE END IF KK = KK + N - J + 1 60 CONTINUE ELSE DO 80, J = 1, N IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN TEMP1 = ALPHA*Y( JY ) TEMP2 = ALPHA*X( JX ) IX = JX IY = JY DO 70, K = KK, KK + N - J AP( K ) = AP( K ) + X( IX )*TEMP1 + Y( IY )*TEMP2 IX = IX + INCX IY = IY + INCY 70 CONTINUE END IF JX = JX + INCX JY = JY + INCY KK = KK + N - J + 1 80 CONTINUE END IF END IF C RETURN C C End of DSPR2 . C END