LAPACK  3.9.1
LAPACK: Linear Algebra PACKage
drotm.f
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1 *> \brief \b DROTM
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
12 *
13 * .. Scalar Arguments ..
14 * INTEGER INCX,INCY,N
15 * ..
16 * .. Array Arguments ..
17 * DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
18 * ..
19 *
20 *
21 *> \par Purpose:
22 * =============
23 *>
24 *> \verbatim
25 *>
26 *> APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
27 *>
28 *> (DX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF DX ARE IN
29 *> (DY**T)
30 *>
31 *> DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
32 *> LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
33 *> WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
34 *>
35 *> DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0
36 *>
37 *> (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
38 *> H=( ) ( ) ( ) ( )
39 *> (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
40 *> SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.
41 *> \endverbatim
42 *
43 * Arguments:
44 * ==========
45 *
46 *> \param[in] N
47 *> \verbatim
48 *> N is INTEGER
49 *> number of elements in input vector(s)
50 *> \endverbatim
51 *>
52 *> \param[in,out] DX
53 *> \verbatim
54 *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
55 *> \endverbatim
56 *>
57 *> \param[in] INCX
58 *> \verbatim
59 *> INCX is INTEGER
60 *> storage spacing between elements of DX
61 *> \endverbatim
62 *>
63 *> \param[in,out] DY
64 *> \verbatim
65 *> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
66 *> \endverbatim
67 *>
68 *> \param[in] INCY
69 *> \verbatim
70 *> INCY is INTEGER
71 *> storage spacing between elements of DY
72 *> \endverbatim
73 *>
74 *> \param[in] DPARAM
75 *> \verbatim
76 *> DPARAM is DOUBLE PRECISION array, dimension (5)
77 *> DPARAM(1)=DFLAG
78 *> DPARAM(2)=DH11
79 *> DPARAM(3)=DH21
80 *> DPARAM(4)=DH12
81 *> DPARAM(5)=DH22
82 *> \endverbatim
83 *
84 * Authors:
85 * ========
86 *
87 *> \author Univ. of Tennessee
88 *> \author Univ. of California Berkeley
89 *> \author Univ. of Colorado Denver
90 *> \author NAG Ltd.
91 *
92 *> \ingroup double_blas_level1
93 *
94 * =====================================================================
95  SUBROUTINE drotm(N,DX,INCX,DY,INCY,DPARAM)
96 *
97 * -- Reference BLAS level1 routine --
98 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
99 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
100 *
101 * .. Scalar Arguments ..
102  INTEGER INCX,INCY,N
103 * ..
104 * .. Array Arguments ..
105  DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
106 * ..
107 *
108 * =====================================================================
109 *
110 * .. Local Scalars ..
111  DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,TWO,W,Z,ZERO
112  INTEGER I,KX,KY,NSTEPS
113 * ..
114 * .. Data statements ..
115  DATA zero,two/0.d0,2.d0/
116 * ..
117 *
118  dflag = dparam(1)
119  IF (n.LE.0 .OR. (dflag+two.EQ.zero)) RETURN
120  IF (incx.EQ.incy.AND.incx.GT.0) THEN
121 *
122  nsteps = n*incx
123  IF (dflag.LT.zero) THEN
124  dh11 = dparam(2)
125  dh12 = dparam(4)
126  dh21 = dparam(3)
127  dh22 = dparam(5)
128  DO i = 1,nsteps,incx
129  w = dx(i)
130  z = dy(i)
131  dx(i) = w*dh11 + z*dh12
132  dy(i) = w*dh21 + z*dh22
133  END DO
134  ELSE IF (dflag.EQ.zero) THEN
135  dh12 = dparam(4)
136  dh21 = dparam(3)
137  DO i = 1,nsteps,incx
138  w = dx(i)
139  z = dy(i)
140  dx(i) = w + z*dh12
141  dy(i) = w*dh21 + z
142  END DO
143  ELSE
144  dh11 = dparam(2)
145  dh22 = dparam(5)
146  DO i = 1,nsteps,incx
147  w = dx(i)
148  z = dy(i)
149  dx(i) = w*dh11 + z
150  dy(i) = -w + dh22*z
151  END DO
152  END IF
153  ELSE
154  kx = 1
155  ky = 1
156  IF (incx.LT.0) kx = 1 + (1-n)*incx
157  IF (incy.LT.0) ky = 1 + (1-n)*incy
158 *
159  IF (dflag.LT.zero) THEN
160  dh11 = dparam(2)
161  dh12 = dparam(4)
162  dh21 = dparam(3)
163  dh22 = dparam(5)
164  DO i = 1,n
165  w = dx(kx)
166  z = dy(ky)
167  dx(kx) = w*dh11 + z*dh12
168  dy(ky) = w*dh21 + z*dh22
169  kx = kx + incx
170  ky = ky + incy
171  END DO
172  ELSE IF (dflag.EQ.zero) THEN
173  dh12 = dparam(4)
174  dh21 = dparam(3)
175  DO i = 1,n
176  w = dx(kx)
177  z = dy(ky)
178  dx(kx) = w + z*dh12
179  dy(ky) = w*dh21 + z
180  kx = kx + incx
181  ky = ky + incy
182  END DO
183  ELSE
184  dh11 = dparam(2)
185  dh22 = dparam(5)
186  DO i = 1,n
187  w = dx(kx)
188  z = dy(ky)
189  dx(kx) = w*dh11 + z
190  dy(ky) = -w + dh22*z
191  kx = kx + incx
192  ky = ky + incy
193  END DO
194  END IF
195  END IF
196  RETURN
197  END
subroutine drotm(N, DX, INCX, DY, INCY, DPARAM)
DROTM
Definition: drotm.f:96