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    1: *> \brief \b DLARGV generates a vector of plane rotations with real cosines and real sines.
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    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">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       INTEGER            INCC, INCX, INCY, N
   25: *       ..
   26: *       .. Array Arguments ..
   27: *       DOUBLE PRECISION   C( * ), X( * ), Y( * )
   28: *       ..
   29: *
   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: *
   95: *> \author Univ. of Tennessee
   96: *> \author Univ. of California Berkeley
   97: *> \author Univ. of Colorado Denver
   98: *> \author NAG Ltd.
   99: *
  100: *> \ingroup doubleOTHERauxiliary
  101: *
  102: *  =====================================================================
  103:       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
  104: *
  105: *  -- LAPACK auxiliary routine --
  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