165 lines
4.2 KiB
Fortran
165 lines
4.2 KiB
Fortran
*> \brief \b SLARGV generates a vector of plane rotations with real cosines and real sines.
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download SLARGV + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slargv.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slargv.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slargv.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE SLARGV( N, X, INCX, Y, INCY, C, INCC )
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*
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* .. Scalar Arguments ..
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* INTEGER INCC, INCX, INCY, N
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* ..
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* .. Array Arguments ..
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* REAL C( * ), X( * ), Y( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> SLARGV generates a vector of real plane rotations, determined by
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*> elements of the real vectors x and y. For i = 1,2,...,n
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*>
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*> ( c(i) s(i) ) ( x(i) ) = ( a(i) )
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*> ( -s(i) c(i) ) ( y(i) ) = ( 0 )
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The number of plane rotations to be generated.
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*> \endverbatim
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*>
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*> \param[in,out] X
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*> \verbatim
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*> X is REAL array,
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*> dimension (1+(N-1)*INCX)
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*> On entry, the vector x.
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*> On exit, x(i) is overwritten by a(i), for i = 1,...,n.
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> The increment between elements of X. INCX > 0.
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*> \endverbatim
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*>
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*> \param[in,out] Y
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*> \verbatim
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*> Y is REAL array,
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*> dimension (1+(N-1)*INCY)
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*> On entry, the vector y.
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*> On exit, the sines of the plane rotations.
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*> \endverbatim
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*>
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*> \param[in] INCY
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*> \verbatim
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*> INCY is INTEGER
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*> The increment between elements of Y. INCY > 0.
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*> \endverbatim
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*>
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*> \param[out] C
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*> \verbatim
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*> C is REAL array, dimension (1+(N-1)*INCC)
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*> The cosines of the plane rotations.
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*> \endverbatim
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*>
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*> \param[in] INCC
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*> \verbatim
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*> INCC is INTEGER
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*> The increment between elements of C. INCC > 0.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup realOTHERauxiliary
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*
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* =====================================================================
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SUBROUTINE SLARGV( N, X, INCX, Y, INCY, C, INCC )
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*
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* -- LAPACK auxiliary routine --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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INTEGER INCC, INCX, INCY, N
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* ..
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* .. Array Arguments ..
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REAL C( * ), X( * ), Y( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ZERO, ONE
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PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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INTEGER I, IC, IX, IY
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REAL F, G, T, TT
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, SQRT
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* ..
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* .. Executable Statements ..
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*
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IX = 1
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IY = 1
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IC = 1
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DO 10 I = 1, N
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F = X( IX )
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G = Y( IY )
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IF( G.EQ.ZERO ) THEN
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C( IC ) = ONE
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ELSE IF( F.EQ.ZERO ) THEN
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C( IC ) = ZERO
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Y( IY ) = ONE
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X( IX ) = G
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ELSE IF( ABS( F ).GT.ABS( G ) ) THEN
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T = G / F
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TT = SQRT( ONE+T*T )
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C( IC ) = ONE / TT
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Y( IY ) = T*C( IC )
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X( IX ) = F*TT
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ELSE
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T = F / G
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TT = SQRT( ONE+T*T )
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Y( IY ) = ONE / TT
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C( IC ) = T*Y( IY )
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X( IX ) = G*TT
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END IF
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IC = IC + INCC
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IY = IY + INCY
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IX = IX + INCX
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10 CONTINUE
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RETURN
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*
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* End of SLARGV
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*
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END
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