*DECK SGER SUBROUTINE SGER (M, N, ALPHA, X, INCX, Y, INCY, A, LDA) C***BEGIN PROLOGUE SGER C***PURPOSE Perform rank 1 update of a real general matrix. C***LIBRARY SLATEC (BLAS) C***CATEGORY D1B4 C***TYPE SINGLE PRECISION (SGER-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 SGER performs the rank 1 operation C C A := alpha*x*y' + A, C C where alpha is a scalar, x is an m element vector, y is an n element C vector and A is an m by n matrix. C C Parameters C ========== C C M - INTEGER. C On entry, M specifies the number of rows of the matrix A. C M must be at least zero. C Unchanged on exit. C C N - INTEGER. C On entry, N specifies the number of columns 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 + ( m - 1)*abs( INCX)). C Before entry, the incremented array X must contain the m 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 - REAL 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 - REAL array of DIMENSION ( LDA, n ). C Before entry, the leading m by n part of the array A must C contain the matrix of coefficients. On exit, A is C overwritten by 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, m ). 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 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 SGER C .. Scalar Arguments .. REAL ALPHA INTEGER INCX, INCY, LDA, M, N C .. Array Arguments .. REAL A( LDA, * ), X( * ), Y( * ) C .. Parameters .. REAL ZERO PARAMETER ( ZERO = 0.0E+0 ) C .. Local Scalars .. REAL TEMP INTEGER I, INFO, IX, J, JY, KX C .. External Subroutines .. EXTERNAL XERBLA C .. Intrinsic Functions .. INTRINSIC MAX C***FIRST EXECUTABLE STATEMENT SGER C C Test the input parameters. C INFO = 0 IF ( M.LT.0 )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 ELSE IF( LDA.LT.MAX( 1, M ) )THEN INFO = 9 END IF IF( INFO.NE.0 )THEN CALL XERBLA( 'SGER ', INFO ) RETURN END IF C C Quick return if possible. C IF( ( M.EQ.0 ).OR.( N.EQ.0 ).OR.( ALPHA.EQ.ZERO ) ) $ RETURN C C Start the operations. In this version the elements of A are C accessed sequentially with one pass through A. C IF( INCY.GT.0 )THEN JY = 1 ELSE JY = 1 - ( N - 1 )*INCY END IF IF( INCX.EQ.1 )THEN DO 20, J = 1, N IF( Y( JY ).NE.ZERO )THEN TEMP = ALPHA*Y( JY ) DO 10, I = 1, M A( I, J ) = A( I, J ) + X( I )*TEMP 10 CONTINUE END IF JY = JY + INCY 20 CONTINUE ELSE IF( INCX.GT.0 )THEN KX = 1 ELSE KX = 1 - ( M - 1 )*INCX END IF DO 40, J = 1, N IF( Y( JY ).NE.ZERO )THEN TEMP = ALPHA*Y( JY ) IX = KX DO 30, I = 1, M A( I, J ) = A( I, J ) + X( IX )*TEMP IX = IX + INCX 30 CONTINUE END IF JY = JY + INCY 40 CONTINUE END IF C RETURN C C End of SGER . C END