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*> \brief \b SLARGV
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> Download SLARGV + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slargv.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slargv.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slargv.f">
*> [TXT]</a>
*
* Definition
* ==========
*
* SUBROUTINE SLARGV( N, X, INCX, Y, INCY, C, INCC )
*
* .. Scalar Arguments ..
* INTEGER INCC, INCX, INCY, N
* ..
* .. Array Arguments ..
* REAL C( * ), X( * ), Y( * )
* ..
*
* Purpose
* =======
*
*>\details \b Purpose:
*>\verbatim
*>
*> 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 )
*>
*>\endverbatim
*
* Arguments
* =========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The number of plane rotations to be generated.
*> \endverbatim
*>
*> \param[in,out] X
*> \verbatim
*> 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.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*> INCX is INTEGER
*> The increment between elements of X. INCX > 0.
*> \endverbatim
*>
*> \param[in,out] Y
*> \verbatim
*> Y is REAL array,
*> dimension (1+(N-1)*INCY)
*> On entry, the vector y.
*> On exit, the sines of the plane rotations.
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*> INCY is INTEGER
*> The increment between elements of Y. INCY > 0.
*> \endverbatim
*>
*> \param[out] C
*> \verbatim
*> C is REAL array, dimension (1+(N-1)*INCC)
*> The cosines of the plane rotations.
*> \endverbatim
*>
*> \param[in] INCC
*> \verbatim
*> INCC is INTEGER
*> The increment between elements of C. INCC > 0.
*> \endverbatim
*>
*
* Authors
* =======
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date November 2011
*
*> \ingroup realOTHERauxiliary
*
* =====================================================================
SUBROUTINE SLARGV( N, X, INCX, Y, INCY, C, INCC )
*
* -- LAPACK auxiliary routine (version 3.2) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* November 2011
*
* .. 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
*
END
|
