Return to dlassq.f CVS log

Up to [local] / rpl / lapack / lapack

Mise à jour globale de Lapack 3.2.2.

    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