LAPACK  3.10.1 LAPACK: Linear Algebra PACKage
dlargv.f
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1 *> \brief \b DLARGV generates a vector of plane rotations with real cosines and real sines.
2 *
3 * =========== DOCUMENTATION ===========
4 *
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17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
22 *
23 * .. Scalar Arguments ..
24 * INTEGER INCC, INCX, INCY, N
25 * ..
26 * .. Array Arguments ..
27 * DOUBLE PRECISION C( * ), X( * ), Y( * )
28 * ..
29 *
30 *
31 *> \par Purpose:
32 * =============
33 *>
34 *> \verbatim
35 *>
36 *> DLARGV generates a vector of real plane rotations, determined by
37 *> elements of the real vectors x and y. For i = 1,2,...,n
38 *>
39 *> ( c(i) s(i) ) ( x(i) ) = ( a(i) )
40 *> ( -s(i) c(i) ) ( y(i) ) = ( 0 )
41 *> \endverbatim
42 *
43 * Arguments:
44 * ==========
45 *
46 *> \param[in] N
47 *> \verbatim
48 *> N is INTEGER
49 *> The number of plane rotations to be generated.
50 *> \endverbatim
51 *>
52 *> \param[in,out] X
53 *> \verbatim
54 *> X is DOUBLE PRECISION array,
55 *> dimension (1+(N-1)*INCX)
56 *> On entry, the vector x.
57 *> On exit, x(i) is overwritten by a(i), for i = 1,...,n.
58 *> \endverbatim
59 *>
60 *> \param[in] INCX
61 *> \verbatim
62 *> INCX is INTEGER
63 *> The increment between elements of X. INCX > 0.
64 *> \endverbatim
65 *>
66 *> \param[in,out] Y
67 *> \verbatim
68 *> Y is DOUBLE PRECISION array,
69 *> dimension (1+(N-1)*INCY)
70 *> On entry, the vector y.
71 *> On exit, the sines of the plane rotations.
72 *> \endverbatim
73 *>
74 *> \param[in] INCY
75 *> \verbatim
76 *> INCY is INTEGER
77 *> The increment between elements of Y. INCY > 0.
78 *> \endverbatim
79 *>
80 *> \param[out] C
81 *> \verbatim
82 *> C is DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
83 *> The cosines of the plane rotations.
84 *> \endverbatim
85 *>
86 *> \param[in] INCC
87 *> \verbatim
88 *> INCC is INTEGER
89 *> The increment between elements of C. INCC > 0.
90 *> \endverbatim
91 *
92 * Authors:
93 * ========
94 *
95 *> \author Univ. of Tennessee
96 *> \author Univ. of California Berkeley
97 *> \author Univ. of Colorado Denver
98 *> \author NAG Ltd.
99 *
100 *> \ingroup doubleOTHERauxiliary
101 *
102 * =====================================================================
103  SUBROUTINE dlargv( N, X, INCX, Y, INCY, C, INCC )
104 *
105 * -- LAPACK auxiliary routine --
106 * -- LAPACK is a software package provided by Univ. of Tennessee, --
107 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
108 *
109 * .. Scalar Arguments ..
110  INTEGER INCC, INCX, INCY, N
111 * ..
112 * .. Array Arguments ..
113  DOUBLE PRECISION C( * ), X( * ), Y( * )
114 * ..
115 *
116 * =====================================================================
117 *
118 * .. Parameters ..
119  DOUBLE PRECISION ZERO, ONE
120  parameter( zero = 0.0d+0, one = 1.0d+0 )
121 * ..
122 * .. Local Scalars ..
123  INTEGER I, IC, IX, IY
124  DOUBLE PRECISION F, G, T, TT
125 * ..
126 * .. Intrinsic Functions ..
127  INTRINSIC abs, sqrt
128 * ..
129 * .. Executable Statements ..
130 *
131  ix = 1
132  iy = 1
133  ic = 1
134  DO 10 i = 1, n
135  f = x( ix )
136  g = y( iy )
137  IF( g.EQ.zero ) THEN
138  c( ic ) = one
139  ELSE IF( f.EQ.zero ) THEN
140  c( ic ) = zero
141  y( iy ) = one
142  x( ix ) = g
143  ELSE IF( abs( f ).GT.abs( g ) ) THEN
144  t = g / f
145  tt = sqrt( one+t*t )
146  c( ic ) = one / tt
147  y( iy ) = t*c( ic )
148  x( ix ) = f*tt
149  ELSE
150  t = f / g
151  tt = sqrt( one+t*t )
152  y( iy ) = one / tt
153  c( ic ) = t*y( iy )
154  x( ix ) = g*tt
155  END IF
156  ic = ic + incc
157  iy = iy + incy
158  ix = ix + incx
159  10 CONTINUE
160  RETURN
161 *
162 * End of DLARGV
163 *
164  END
subroutine dlargv(N, X, INCX, Y, INCY, C, INCC)
DLARGV generates a vector of plane rotations with real cosines and real sines.
Definition: dlargv.f:104