lapack/dladiv.f

*> \brief \b DLADIV
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*> \htmlonly
*> Download DLADIV + dependencies 
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dladiv.f"> 
*> [TXT]</a>
*> \endhtmlonly 
*
*  Definition:
*  ===========
*
*       SUBROUTINE DLADIV( A, B, C, D, P, Q )
* 
*       .. Scalar Arguments ..
*       DOUBLE PRECISION   A, B, C, D, P, Q
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> DLADIV performs complex division in  real arithmetic
*>
*>                       a + i*b
*>            p + i*q = ---------
*>                       c + i*d
*>
*> The algorithm is due to Robert L. Smith and can be found
*> in D. Knuth, The art of Computer Programming, Vol.2, p.195
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] A
*> \verbatim
*>          A is DOUBLE PRECISION
*> \endverbatim
*>
*> \param[in] B
*> \verbatim
*>          B is DOUBLE PRECISION
*> \endverbatim
*>
*> \param[in] C
*> \verbatim
*>          C is DOUBLE PRECISION
*> \endverbatim
*>
*> \param[in] D
*> \verbatim
*>          D is DOUBLE PRECISION
*>          The scalars a, b, c, and d in the above expression.
*> \endverbatim
*>
*> \param[out] P
*> \verbatim
*>          P is DOUBLE PRECISION
*> \endverbatim
*>
*> \param[out] Q
*> \verbatim
*>          Q is DOUBLE PRECISION
*>          The scalars p and q in the above expression.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2011
*
*> \ingroup auxOTHERauxiliary
*
*  =====================================================================
      SUBROUTINE DLADIV( A, B, C, D, P, Q )
*
*  -- LAPACK auxiliary routine (version 3.4.0) --
*  -- 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 ..
      DOUBLE PRECISION   A, B, C, D, P, Q
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION   E, F
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS
*     ..
*     .. Executable Statements ..
*
      IF( ABS( D ).LT.ABS( C ) ) THEN
         E = D / C
         F = C + D*E
         P = ( A+B*E ) / F
         Q = ( B-A*E ) / F
      ELSE
         E = C / D
         F = D + C*E
         P = ( B+A*E ) / F
         Q = ( -A+B*E ) / F
      END IF
*
      RETURN
*
*     End of DLADIV
*
      END