forked from lijiext/lammps
129 lines
3.0 KiB
Fortran
129 lines
3.0 KiB
Fortran
*> \brief \b DLADIV performs complex division in real arithmetic, avoiding unnecessary overflow.
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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 DLADIV + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dladiv.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/dladiv.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/dladiv.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 DLADIV( A, B, C, D, P, Q )
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION A, B, C, D, P, Q
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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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*> DLADIV performs complex division in real arithmetic
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*>
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*> a + i*b
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*> p + i*q = ---------
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*> c + i*d
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*>
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*> The algorithm is due to Robert L. Smith and can be found
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*> in D. Knuth, The art of Computer Programming, Vol.2, p.195
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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] A
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*> \verbatim
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*> A is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[in] B
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*> \verbatim
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*> B is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[in] C
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*> \verbatim
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*> C is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[in] D
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*> \verbatim
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*> D is DOUBLE PRECISION
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*> The scalars a, b, c, and d in the above expression.
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*> \endverbatim
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*>
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*> \param[out] P
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*> \verbatim
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*> P is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[out] Q
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*> \verbatim
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*> Q is DOUBLE PRECISION
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*> The scalars p and q in the above expression.
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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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*> \date September 2012
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*
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*> \ingroup auxOTHERauxiliary
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*
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* =====================================================================
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SUBROUTINE DLADIV( A, B, C, D, P, Q )
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*
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* -- LAPACK auxiliary routine (version 3.4.2) --
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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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* September 2012
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*
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* .. Scalar Arguments ..
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DOUBLE PRECISION A, B, C, D, P, Q
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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DOUBLE PRECISION E, F
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS
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* ..
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* .. Executable Statements ..
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*
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IF( ABS( D ).LT.ABS( C ) ) THEN
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E = D / C
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F = C + D*E
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P = ( A+B*E ) / F
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Q = ( B-A*E ) / F
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ELSE
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E = C / D
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F = D + C*E
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P = ( B+A*E ) / F
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Q = ( -A+B*E ) / F
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END IF
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*
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RETURN
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*
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* End of DLADIV
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*
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END
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