01:       SUBROUTINE DLASSQ( N, X, INCX, SCALE, SUMSQ )
02: *
03: *  -- LAPACK auxiliary routine (version 3.2) --
04: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
05: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
06: *     November 2006
07: *
08: *     .. Scalar Arguments ..
09:       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
90: