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Annotation of rpl/lapack/lapack/dlargv.f, revision 1.18

1.11      bertrand    1: *> \brief \b DLARGV generates a vector of plane rotations with real cosines and real sines.
1.8       bertrand    2: *
                      3: *  =========== DOCUMENTATION ===========
                      4: *
1.15      bertrand    5: * Online html documentation available at
                      6: *            http://www.netlib.org/lapack/explore-html/
1.8       bertrand    7: *
                      8: *> \htmlonly
1.15      bertrand    9: *> Download DLARGV + dependencies
                     10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlargv.f">
                     11: *> [TGZ]</a>
                     12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlargv.f">
                     13: *> [ZIP]</a>
                     14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlargv.f">
1.8       bertrand   15: *> [TXT]</a>
1.15      bertrand   16: *> \endhtmlonly
1.8       bertrand   17: *
                     18: *  Definition:
                     19: *  ===========
                     20: *
                     21: *       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
1.15      bertrand   22: *
1.8       bertrand   23: *       .. Scalar Arguments ..
                     24: *       INTEGER            INCC, INCX, INCY, N
                     25: *       ..
                     26: *       .. Array Arguments ..
                     27: *       DOUBLE PRECISION   C( * ), X( * ), Y( * )
                     28: *       ..
1.15      bertrand   29: *
1.8       bertrand   30: *
                     31: *> \par Purpose:
                     32: *  =============
                     33: *>
                     34: *> \verbatim
                     35: *>
                     36: *> DLARGV generates a vector of real plane rotations, determined by
                     37: *> elements of the real vectors x and y. For i = 1,2,...,n
                     38: *>
                     39: *>    (  c(i)  s(i) ) ( x(i) ) = ( a(i) )
                     40: *>    ( -s(i)  c(i) ) ( y(i) ) = (   0  )
                     41: *> \endverbatim
                     42: *
                     43: *  Arguments:
                     44: *  ==========
                     45: *
                     46: *> \param[in] N
                     47: *> \verbatim
                     48: *>          N is INTEGER
                     49: *>          The number of plane rotations to be generated.
                     50: *> \endverbatim
                     51: *>
                     52: *> \param[in,out] X
                     53: *> \verbatim
                     54: *>          X is DOUBLE PRECISION array,
                     55: *>                         dimension (1+(N-1)*INCX)
                     56: *>          On entry, the vector x.
                     57: *>          On exit, x(i) is overwritten by a(i), for i = 1,...,n.
                     58: *> \endverbatim
                     59: *>
                     60: *> \param[in] INCX
                     61: *> \verbatim
                     62: *>          INCX is INTEGER
                     63: *>          The increment between elements of X. INCX > 0.
                     64: *> \endverbatim
                     65: *>
                     66: *> \param[in,out] Y
                     67: *> \verbatim
                     68: *>          Y is DOUBLE PRECISION array,
                     69: *>                         dimension (1+(N-1)*INCY)
                     70: *>          On entry, the vector y.
                     71: *>          On exit, the sines of the plane rotations.
                     72: *> \endverbatim
                     73: *>
                     74: *> \param[in] INCY
                     75: *> \verbatim
                     76: *>          INCY is INTEGER
                     77: *>          The increment between elements of Y. INCY > 0.
                     78: *> \endverbatim
                     79: *>
                     80: *> \param[out] C
                     81: *> \verbatim
                     82: *>          C is DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
                     83: *>          The cosines of the plane rotations.
                     84: *> \endverbatim
                     85: *>
                     86: *> \param[in] INCC
                     87: *> \verbatim
                     88: *>          INCC is INTEGER
                     89: *>          The increment between elements of C. INCC > 0.
                     90: *> \endverbatim
                     91: *
                     92: *  Authors:
                     93: *  ========
                     94: *
1.15      bertrand   95: *> \author Univ. of Tennessee
                     96: *> \author Univ. of California Berkeley
                     97: *> \author Univ. of Colorado Denver
                     98: *> \author NAG Ltd.
1.8       bertrand   99: *
                    100: *> \ingroup doubleOTHERauxiliary
                    101: *
                    102: *  =====================================================================
1.1       bertrand  103:       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
                    104: *
1.18    ! bertrand  105: *  -- LAPACK auxiliary routine --
1.1       bertrand  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:       DOUBLE PRECISION   C( * ), X( * ), Y( * )
                    114: *     ..
                    115: *
                    116: *  =====================================================================
                    117: *
                    118: *     .. Parameters ..
                    119:       DOUBLE PRECISION   ZERO, ONE
                    120:       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
                    121: *     ..
                    122: *     .. Local Scalars ..
                    123:       INTEGER            I, IC, IX, IY
                    124:       DOUBLE PRECISION   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 DLARGV
                    163: *
                    164:       END