LAPACK  3.8.0
LAPACK: Linear Algebra PACKage
srotm.f
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1 *> \brief \b SROTM
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 SROTM(N,SX,INCX,SY,INCY,SPARAM)
12 *
13 * .. Scalar Arguments ..
14 * INTEGER INCX,INCY,N
15 * ..
16 * .. Array Arguments ..
17 * REAL SPARAM(5),SX(*),SY(*)
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 *> (SX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF SX ARE IN
29 *> (SX**T)
30 *>
31 *> SX(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 USING LY AND INCY.
33 *> WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
34 *>
35 *> SFLAG=-1.E0 SFLAG=0.E0 SFLAG=1.E0 SFLAG=-2.E0
36 *>
37 *> (SH11 SH12) (1.E0 SH12) (SH11 1.E0) (1.E0 0.E0)
38 *> H=( ) ( ) ( ) ( )
39 *> (SH21 SH22), (SH21 1.E0), (-1.E0 SH22), (0.E0 1.E0).
40 *> SEE SROTMG FOR A DESCRIPTION OF DATA STORAGE IN SPARAM.
41 *>
42 *> \endverbatim
43 *
44 * Arguments:
45 * ==========
46 *
47 *> \param[in] N
48 *> \verbatim
49 *> N is INTEGER
50 *> number of elements in input vector(s)
51 *> \endverbatim
52 *>
53 *> \param[in,out] SX
54 *> \verbatim
55 *> SX is REAL array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
56 *> \endverbatim
57 *>
58 *> \param[in] INCX
59 *> \verbatim
60 *> INCX is INTEGER
61 *> storage spacing between elements of SX
62 *> \endverbatim
63 *>
64 *> \param[in,out] SY
65 *> \verbatim
66 *> SY is REAL array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
67 *> \endverbatim
68 *>
69 *> \param[in] INCY
70 *> \verbatim
71 *> INCY is INTEGER
72 *> storage spacing between elements of SY
73 *> \endverbatim
74 *>
75 *> \param[in] SPARAM
76 *> \verbatim
77 *> SPARAM is REAL array, dimension (5)
78 *> SPARAM(1)=SFLAG
79 *> SPARAM(2)=SH11
80 *> SPARAM(3)=SH21
81 *> SPARAM(4)=SH12
82 *> SPARAM(5)=SH22
83 *> \endverbatim
84 *
85 * Authors:
86 * ========
87 *
88 *> \author Univ. of Tennessee
89 *> \author Univ. of California Berkeley
90 *> \author Univ. of Colorado Denver
91 *> \author NAG Ltd.
92 *
93 *> \date November 2017
94 *
95 *> \ingroup single_blas_level1
96 *
97 * =====================================================================
98  SUBROUTINE srotm(N,SX,INCX,SY,INCY,SPARAM)
99 *
100 * -- Reference BLAS level1 routine (version 3.8.0) --
101 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
102 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
103 * November 2017
104 *
105 * .. Scalar Arguments ..
106  INTEGER INCX,INCY,N
107 * ..
108 * .. Array Arguments ..
109  REAL SPARAM(5),SX(*),SY(*)
110 * ..
111 *
112 * =====================================================================
113 *
114 * .. Local Scalars ..
115  REAL SFLAG,SH11,SH12,SH21,SH22,TWO,W,Z,ZERO
116  INTEGER I,KX,KY,NSTEPS
117 * ..
118 * .. Data statements ..
119  DATA zero,two/0.e0,2.e0/
120 * ..
121 *
122  sflag = sparam(1)
123  IF (n.LE.0 .OR. (sflag+two.EQ.zero)) RETURN
124  IF (incx.EQ.incy.AND.incx.GT.0) THEN
125 *
126  nsteps = n*incx
127  IF (sflag.LT.zero) THEN
128  sh11 = sparam(2)
129  sh12 = sparam(4)
130  sh21 = sparam(3)
131  sh22 = sparam(5)
132  DO i = 1,nsteps,incx
133  w = sx(i)
134  z = sy(i)
135  sx(i) = w*sh11 + z*sh12
136  sy(i) = w*sh21 + z*sh22
137  END DO
138  ELSE IF (sflag.EQ.zero) THEN
139  sh12 = sparam(4)
140  sh21 = sparam(3)
141  DO i = 1,nsteps,incx
142  w = sx(i)
143  z = sy(i)
144  sx(i) = w + z*sh12
145  sy(i) = w*sh21 + z
146  END DO
147  ELSE
148  sh11 = sparam(2)
149  sh22 = sparam(5)
150  DO i = 1,nsteps,incx
151  w = sx(i)
152  z = sy(i)
153  sx(i) = w*sh11 + z
154  sy(i) = -w + sh22*z
155  END DO
156  END IF
157  ELSE
158  kx = 1
159  ky = 1
160  IF (incx.LT.0) kx = 1 + (1-n)*incx
161  IF (incy.LT.0) ky = 1 + (1-n)*incy
162 *
163  IF (sflag.LT.zero) THEN
164  sh11 = sparam(2)
165  sh12 = sparam(4)
166  sh21 = sparam(3)
167  sh22 = sparam(5)
168  DO i = 1,n
169  w = sx(kx)
170  z = sy(ky)
171  sx(kx) = w*sh11 + z*sh12
172  sy(ky) = w*sh21 + z*sh22
173  kx = kx + incx
174  ky = ky + incy
175  END DO
176  ELSE IF (sflag.EQ.zero) THEN
177  sh12 = sparam(4)
178  sh21 = sparam(3)
179  DO i = 1,n
180  w = sx(kx)
181  z = sy(ky)
182  sx(kx) = w + z*sh12
183  sy(ky) = w*sh21 + z
184  kx = kx + incx
185  ky = ky + incy
186  END DO
187  ELSE
188  sh11 = sparam(2)
189  sh22 = sparam(5)
190  DO i = 1,n
191  w = sx(kx)
192  z = sy(ky)
193  sx(kx) = w*sh11 + z
194  sy(ky) = -w + sh22*z
195  kx = kx + incx
196  ky = ky + incy
197  END DO
198  END IF
199  END IF
200  RETURN
201  END
subroutine srotm(N, SX, INCX, SY, INCY, SPARAM)
SROTM
Definition: srotm.f:99