LAPACK  3.10.1 LAPACK: Linear Algebra PACKage
drscl.f
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1 *> \brief \b DRSCL multiplies a vector by the reciprocal of a real scalar.
2 *
3 * =========== DOCUMENTATION ===========
4 *
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17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE DRSCL( N, SA, SX, INCX )
22 *
23 * .. Scalar Arguments ..
24 * INTEGER INCX, N
25 * DOUBLE PRECISION SA
26 * ..
27 * .. Array Arguments ..
28 * DOUBLE PRECISION SX( * )
29 * ..
30 *
31 *
32 *> \par Purpose:
33 * =============
34 *>
35 *> \verbatim
36 *>
37 *> DRSCL multiplies an n-element real vector x by the real scalar 1/a.
38 *> This is done without overflow or underflow as long as
39 *> the final result x/a does not overflow or underflow.
40 *> \endverbatim
41 *
42 * Arguments:
43 * ==========
44 *
45 *> \param[in] N
46 *> \verbatim
47 *> N is INTEGER
48 *> The number of components of the vector x.
49 *> \endverbatim
50 *>
51 *> \param[in] SA
52 *> \verbatim
53 *> SA is DOUBLE PRECISION
54 *> The scalar a which is used to divide each component of x.
55 *> SA must be >= 0, or the subroutine will divide by zero.
56 *> \endverbatim
57 *>
58 *> \param[in,out] SX
59 *> \verbatim
60 *> SX is DOUBLE PRECISION array, dimension
61 *> (1+(N-1)*abs(INCX))
62 *> The n-element vector x.
63 *> \endverbatim
64 *>
65 *> \param[in] INCX
66 *> \verbatim
67 *> INCX is INTEGER
68 *> The increment between successive values of the vector SX.
69 *> > 0: SX(1) = X(1) and SX(1+(i-1)*INCX) = x(i), 1< i<= n
70 *> \endverbatim
71 *
72 * Authors:
73 * ========
74 *
75 *> \author Univ. of Tennessee
76 *> \author Univ. of California Berkeley
77 *> \author Univ. of Colorado Denver
78 *> \author NAG Ltd.
79 *
80 *> \ingroup doubleOTHERauxiliary
81 *
82 * =====================================================================
83  SUBROUTINE drscl( N, SA, SX, INCX )
84 *
85 * -- LAPACK auxiliary routine --
86 * -- LAPACK is a software package provided by Univ. of Tennessee, --
87 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
88 *
89 * .. Scalar Arguments ..
90  INTEGER INCX, N
91  DOUBLE PRECISION SA
92 * ..
93 * .. Array Arguments ..
94  DOUBLE PRECISION SX( * )
95 * ..
96 *
97 * =====================================================================
98 *
99 * .. Parameters ..
100  DOUBLE PRECISION ONE, ZERO
101  parameter( one = 1.0d+0, zero = 0.0d+0 )
102 * ..
103 * .. Local Scalars ..
104  LOGICAL DONE
105  DOUBLE PRECISION BIGNUM, CDEN, CDEN1, CNUM, CNUM1, MUL, SMLNUM
106 * ..
107 * .. External Functions ..
108  DOUBLE PRECISION DLAMCH
109  EXTERNAL dlamch
110 * ..
111 * .. External Subroutines ..
112  EXTERNAL dscal, dlabad
113 * ..
114 * .. Intrinsic Functions ..
115  INTRINSIC abs
116 * ..
117 * .. Executable Statements ..
118 *
119 * Quick return if possible
120 *
121  IF( n.LE.0 )
122  \$ RETURN
123 *
124 * Get machine parameters
125 *
126  smlnum = dlamch( 'S' )
127  bignum = one / smlnum
128  CALL dlabad( smlnum, bignum )
129 *
130 * Initialize the denominator to SA and the numerator to 1.
131 *
132  cden = sa
133  cnum = one
134 *
135  10 CONTINUE
136  cden1 = cden*smlnum
137  cnum1 = cnum / bignum
138  IF( abs( cden1 ).GT.abs( cnum ) .AND. cnum.NE.zero ) THEN
139 *
140 * Pre-multiply X by SMLNUM if CDEN is large compared to CNUM.
141 *
142  mul = smlnum
143  done = .false.
144  cden = cden1
145  ELSE IF( abs( cnum1 ).GT.abs( cden ) ) THEN
146 *
147 * Pre-multiply X by BIGNUM if CDEN is small compared to CNUM.
148 *
149  mul = bignum
150  done = .false.
151  cnum = cnum1
152  ELSE
153 *
154 * Multiply X by CNUM / CDEN and return.
155 *
156  mul = cnum / cden
157  done = .true.
158  END IF
159 *
160 * Scale the vector X by MUL
161 *
162  CALL dscal( n, mul, sx, incx )
163 *
164  IF( .NOT.done )
165  \$ GO TO 10
166 *
167  RETURN
168 *
169 * End of DRSCL
170 *
171  END