LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
dlargv.f
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00001 *> \brief \b DLARGV
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download DLARGV + dependencies 
00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlargv.f"> 
00011 *> [TGZ]</a> 
00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlargv.f"> 
00013 *> [ZIP]</a> 
00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlargv.f"> 
00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
00022 * 
00023 *       .. Scalar Arguments ..
00024 *       INTEGER            INCC, INCX, INCY, N
00025 *       ..
00026 *       .. Array Arguments ..
00027 *       DOUBLE PRECISION   C( * ), X( * ), Y( * )
00028 *       ..
00029 *  
00030 *
00031 *> \par Purpose:
00032 *  =============
00033 *>
00034 *> \verbatim
00035 *>
00036 *> DLARGV generates a vector of real plane rotations, determined by
00037 *> elements of the real vectors x and y. For i = 1,2,...,n
00038 *>
00039 *>    (  c(i)  s(i) ) ( x(i) ) = ( a(i) )
00040 *>    ( -s(i)  c(i) ) ( y(i) ) = (   0  )
00041 *> \endverbatim
00042 *
00043 *  Arguments:
00044 *  ==========
00045 *
00046 *> \param[in] N
00047 *> \verbatim
00048 *>          N is INTEGER
00049 *>          The number of plane rotations to be generated.
00050 *> \endverbatim
00051 *>
00052 *> \param[in,out] X
00053 *> \verbatim
00054 *>          X is DOUBLE PRECISION array,
00055 *>                         dimension (1+(N-1)*INCX)
00056 *>          On entry, the vector x.
00057 *>          On exit, x(i) is overwritten by a(i), for i = 1,...,n.
00058 *> \endverbatim
00059 *>
00060 *> \param[in] INCX
00061 *> \verbatim
00062 *>          INCX is INTEGER
00063 *>          The increment between elements of X. INCX > 0.
00064 *> \endverbatim
00065 *>
00066 *> \param[in,out] Y
00067 *> \verbatim
00068 *>          Y is DOUBLE PRECISION array,
00069 *>                         dimension (1+(N-1)*INCY)
00070 *>          On entry, the vector y.
00071 *>          On exit, the sines of the plane rotations.
00072 *> \endverbatim
00073 *>
00074 *> \param[in] INCY
00075 *> \verbatim
00076 *>          INCY is INTEGER
00077 *>          The increment between elements of Y. INCY > 0.
00078 *> \endverbatim
00079 *>
00080 *> \param[out] C
00081 *> \verbatim
00082 *>          C is DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
00083 *>          The cosines of the plane rotations.
00084 *> \endverbatim
00085 *>
00086 *> \param[in] INCC
00087 *> \verbatim
00088 *>          INCC is INTEGER
00089 *>          The increment between elements of C. INCC > 0.
00090 *> \endverbatim
00091 *
00092 *  Authors:
00093 *  ========
00094 *
00095 *> \author Univ. of Tennessee 
00096 *> \author Univ. of California Berkeley 
00097 *> \author Univ. of Colorado Denver 
00098 *> \author NAG Ltd. 
00099 *
00100 *> \date November 2011
00101 *
00102 *> \ingroup doubleOTHERauxiliary
00103 *
00104 *  =====================================================================
00105       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
00106 *
00107 *  -- LAPACK auxiliary routine (version 3.4.0) --
00108 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00109 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00110 *     November 2011
00111 *
00112 *     .. Scalar Arguments ..
00113       INTEGER            INCC, INCX, INCY, N
00114 *     ..
00115 *     .. Array Arguments ..
00116       DOUBLE PRECISION   C( * ), X( * ), Y( * )
00117 *     ..
00118 *
00119 *  =====================================================================
00120 *
00121 *     .. Parameters ..
00122       DOUBLE PRECISION   ZERO, ONE
00123       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
00124 *     ..
00125 *     .. Local Scalars ..
00126       INTEGER            I, IC, IX, IY
00127       DOUBLE PRECISION   F, G, T, TT
00128 *     ..
00129 *     .. Intrinsic Functions ..
00130       INTRINSIC          ABS, SQRT
00131 *     ..
00132 *     .. Executable Statements ..
00133 *
00134       IX = 1
00135       IY = 1
00136       IC = 1
00137       DO 10 I = 1, N
00138          F = X( IX )
00139          G = Y( IY )
00140          IF( G.EQ.ZERO ) THEN
00141             C( IC ) = ONE
00142          ELSE IF( F.EQ.ZERO ) THEN
00143             C( IC ) = ZERO
00144             Y( IY ) = ONE
00145             X( IX ) = G
00146          ELSE IF( ABS( F ).GT.ABS( G ) ) THEN
00147             T = G / F
00148             TT = SQRT( ONE+T*T )
00149             C( IC ) = ONE / TT
00150             Y( IY ) = T*C( IC )
00151             X( IX ) = F*TT
00152          ELSE
00153             T = F / G
00154             TT = SQRT( ONE+T*T )
00155             Y( IY ) = ONE / TT
00156             C( IC ) = T*Y( IY )
00157             X( IX ) = G*TT
00158          END IF
00159          IC = IC + INCC
00160          IY = IY + INCY
00161          IX = IX + INCX
00162    10 CONTINUE
00163       RETURN
00164 *
00165 *     End of DLARGV
00166 *
00167       END
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