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Annotation of rpl/lapack/lapack/dlassq.f, revision 1.1.1.1

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