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 101 of file slargv.f.

*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER            INCC, INCX, INCY, N
*     ..
*     .. Array Arguments ..
      REAL               C( * ), X( * ), Y( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO, ONE
      parameter( zero = 0.0e+0, one = 1.0e+0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I, IC, IX, IY
      REAL               F, G, T, TT
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, sqrt
*     ..
*     .. Executable Statements ..
*
      ix = 1
      iy = 1
      ic = 1
      DO 10 i = 1, n
         f = x( ix )
         g = y( iy )
         IF( g.EQ.zero ) THEN
            c( ic ) = one
         ELSE IF( f.EQ.zero ) THEN
            c( ic ) = zero
            y( iy ) = one
            x( ix ) = g
         ELSE IF( abs( f ).GT.abs( g ) ) THEN
            t = g / f
            tt = sqrt( one+t*t )
            c( ic ) = one / tt
            y( iy ) = t*c( ic )
            x( ix ) = f*tt
         ELSE
            t = f / g
            tt = sqrt( one+t*t )
            y( iy ) = one / tt
            c( ic ) = t*y( iy )
            x( ix ) = g*tt
         END IF
         ic = ic + incc
         iy = iy + incy
         ix = ix + incx
   10 CONTINUE
      RETURN
*
*     End of SLARGV
*

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