Return to dlassq.f CVS log

Up to [local] / rpl / lapack / lapack

Annotation of rpl/lapack/lapack/dlassq.f, revision 1.1

1.1     ! bertrand    1:       SUBROUTINE DLASSQ( N, X, INCX, SCALE, SUMSQ )
        !             2: *
        !             3: *  -- LAPACK auxiliary routine (version 3.2) --
        !             4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
        !             5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
        !             6: *     November 2006
        !             7: *
        !             8: *     .. Scalar Arguments ..
        !             9:       INTEGER            INCX, N
        !            10:       DOUBLE PRECISION   SCALE, SUMSQ
        !            11: *     ..
        !            12: *     .. Array Arguments ..
        !            13:       DOUBLE PRECISION   X( * )
        !            14: *     ..
        !            15: *
        !            16: *  Purpose
        !            17: *  =======
        !            18: *
        !            19: *  DLASSQ  returns the values  scl  and  smsq  such that
        !            20: *
        !            21: *     ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
        !            22: *
        !            23: *  where  x( i ) = X( 1 + ( i - 1 )*INCX ). The value of  sumsq  is
        !            24: *  assumed to be non-negative and  scl  returns the value
        !            25: *
        !            26: *     scl = max( scale, abs( x( i ) ) ).
        !            27: *
        !            28: *  scale and sumsq must be supplied in SCALE and SUMSQ and
        !            29: *  scl and smsq are overwritten on SCALE and SUMSQ respectively.
        !            30: *
        !            31: *  The routine makes only one pass through the vector x.
        !            32: *
        !            33: *  Arguments
        !            34: *  =========
        !            35: *
        !            36: *  N       (input) INTEGER
        !            37: *          The number of elements to be used from the vector X.
        !            38: *
        !            39: *  X       (input) DOUBLE PRECISION array, dimension (N)
        !            40: *          The vector for which a scaled sum of squares is computed.
        !            41: *             x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
        !            42: *
        !            43: *  INCX    (input) INTEGER
        !            44: *          The increment between successive values of the vector X.
        !            45: *          INCX > 0.
        !            46: *
        !            47: *  SCALE   (input/output) DOUBLE PRECISION
        !            48: *          On entry, the value  scale  in the equation above.
        !            49: *          On exit, SCALE is overwritten with  scl , the scaling factor
        !            50: *          for the sum of squares.
        !            51: *
        !            52: *  SUMSQ   (input/output) DOUBLE PRECISION
        !            53: *          On entry, the value  sumsq  in the equation above.
        !            54: *          On exit, SUMSQ is overwritten with  smsq , the basic sum of
        !            55: *          squares from which  scl  has been factored out.
        !            56: *
        !            57: * =====================================================================
        !            58: *
        !            59: *     .. Parameters ..
        !            60:       DOUBLE PRECISION   ZERO
        !            61:       PARAMETER          ( ZERO = 0.0D+0 )
        !            62: *     ..
        !            63: *     .. Local Scalars ..
        !            64:       INTEGER            IX
        !            65:       DOUBLE PRECISION   ABSXI
        !            66: *     ..
        !            67: *     .. Intrinsic Functions ..
        !            68:       INTRINSIC          ABS
        !            69: *     ..
        !            70: *     .. Executable Statements ..
        !            71: *
        !            72:       IF( N.GT.0 ) THEN
        !            73:          DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
        !            74:             IF( X( IX ).NE.ZERO ) THEN
        !            75:                ABSXI = ABS( X( IX ) )
        !            76:                IF( SCALE.LT.ABSXI ) THEN
        !            77:                   SUMSQ = 1 + SUMSQ*( SCALE / ABSXI )**2
        !            78:                   SCALE = ABSXI
        !            79:                ELSE
        !            80:                   SUMSQ = SUMSQ + ( ABSXI / SCALE )**2
        !            81:                END IF
        !            82:             END IF
        !            83:    10    CONTINUE
        !            84:       END IF
        !            85:       RETURN
        !            86: *
        !            87: *     End of DLASSQ
        !            88: *
        !            89:       END