LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ slargv()

subroutine slargv ( integer  n,
real, dimension( * )  x,
integer  incx,
real, dimension( * )  y,
integer  incy,
real, dimension( * )  c,
integer  incc 
)

SLARGV generates a vector of plane rotations with real cosines and real sines.

Download SLARGV + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SLARGV generates a vector of real plane rotations, determined by
 elements of the real vectors x and y. For i = 1,2,...,n

    (  c(i)  s(i) ) ( x(i) ) = ( a(i) )
    ( -s(i)  c(i) ) ( y(i) ) = (   0  )
Parameters
[in]N
          N is INTEGER
          The number of plane rotations to be generated.
[in,out]X
          X is REAL array,
                         dimension (1+(N-1)*INCX)
          On entry, the vector x.
          On exit, x(i) is overwritten by a(i), for i = 1,...,n.
[in]INCX
          INCX is INTEGER
          The increment between elements of X. INCX > 0.
[in,out]Y
          Y is REAL array,
                         dimension (1+(N-1)*INCY)
          On entry, the vector y.
          On exit, the sines of the plane rotations.
[in]INCY
          INCY is INTEGER
          The increment between elements of Y. INCY > 0.
[out]C
          C is REAL array, dimension (1+(N-1)*INCC)
          The cosines of the plane rotations.
[in]INCC
          INCC is INTEGER
          The increment between elements of C. INCC > 0.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 103 of file slargv.f.

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 REAL C( * ), X( * ), Y( * )
114* ..
115*
116* =====================================================================
117*
118* .. Parameters ..
119 REAL ZERO, ONE
120 parameter( zero = 0.0e+0, one = 1.0e+0 )
121* ..
122* .. Local Scalars ..
123 INTEGER I, IC, IX, IY
124 REAL 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 SLARGV
163*
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