LAPACK  3.10.0
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 *> \ingroup single_blas_level1
94 *
95 * =====================================================================
96  SUBROUTINE srotm(N,SX,INCX,SY,INCY,SPARAM)
97 *
98 * -- Reference BLAS level1 routine --
99 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
100 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
101 *
102 * .. Scalar Arguments ..
103  INTEGER INCX,INCY,N
104 * ..
105 * .. Array Arguments ..
106  REAL SPARAM(5),SX(*),SY(*)
107 * ..
108 *
109 * =====================================================================
110 *
111 * .. Local Scalars ..
112  REAL SFLAG,SH11,SH12,SH21,SH22,TWO,W,Z,ZERO
113  INTEGER I,KX,KY,NSTEPS
114 * ..
115 * .. Data statements ..
116  DATA zero,two/0.e0,2.e0/
117 * ..
118 *
119  sflag = sparam(1)
120  IF (n.LE.0 .OR. (sflag+two.EQ.zero)) RETURN
121  IF (incx.EQ.incy.AND.incx.GT.0) THEN
122 *
123  nsteps = n*incx
124  IF (sflag.LT.zero) THEN
125  sh11 = sparam(2)
126  sh12 = sparam(4)
127  sh21 = sparam(3)
128  sh22 = sparam(5)
129  DO i = 1,nsteps,incx
130  w = sx(i)
131  z = sy(i)
132  sx(i) = w*sh11 + z*sh12
133  sy(i) = w*sh21 + z*sh22
134  END DO
135  ELSE IF (sflag.EQ.zero) THEN
136  sh12 = sparam(4)
137  sh21 = sparam(3)
138  DO i = 1,nsteps,incx
139  w = sx(i)
140  z = sy(i)
141  sx(i) = w + z*sh12
142  sy(i) = w*sh21 + z
143  END DO
144  ELSE
145  sh11 = sparam(2)
146  sh22 = sparam(5)
147  DO i = 1,nsteps,incx
148  w = sx(i)
149  z = sy(i)
150  sx(i) = w*sh11 + z
151  sy(i) = -w + sh22*z
152  END DO
153  END IF
154  ELSE
155  kx = 1
156  ky = 1
157  IF (incx.LT.0) kx = 1 + (1-n)*incx
158  IF (incy.LT.0) ky = 1 + (1-n)*incy
159 *
160  IF (sflag.LT.zero) THEN
161  sh11 = sparam(2)
162  sh12 = sparam(4)
163  sh21 = sparam(3)
164  sh22 = sparam(5)
165  DO i = 1,n
166  w = sx(kx)
167  z = sy(ky)
168  sx(kx) = w*sh11 + z*sh12
169  sy(ky) = w*sh21 + z*sh22
170  kx = kx + incx
171  ky = ky + incy
172  END DO
173  ELSE IF (sflag.EQ.zero) THEN
174  sh12 = sparam(4)
175  sh21 = sparam(3)
176  DO i = 1,n
177  w = sx(kx)
178  z = sy(ky)
179  sx(kx) = w + z*sh12
180  sy(ky) = w*sh21 + z
181  kx = kx + incx
182  ky = ky + incy
183  END DO
184  ELSE
185  sh11 = sparam(2)
186  sh22 = sparam(5)
187  DO i = 1,n
188  w = sx(kx)
189  z = sy(ky)
190  sx(kx) = w*sh11 + z
191  sy(ky) = -w + sh22*z
192  kx = kx + incx
193  ky = ky + incy
194  END DO
195  END IF
196  END IF
197  RETURN
198 *
199 * End of SROTM
200 *
201  END
subroutine srotm(N, SX, INCX, SY, INCY, SPARAM)
SROTM
Definition: srotm.f:97