118 lines
2.9 KiB
Fortran
118 lines
2.9 KiB
Fortran
*> \brief \b DLAPY2 returns sqrt(x2+y2).
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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 DLAPY2 + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy2.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/dlapy2.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/dlapy2.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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* DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION X, Y
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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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*> DLAPY2 returns sqrt(x**2+y**2), taking care not to cause unnecessary
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*> overflow and unnecessary underflow.
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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] X
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*> \verbatim
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*> X is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[in] Y
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*> \verbatim
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*> Y is DOUBLE PRECISION
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*> X and Y specify the values x and y.
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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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*> \ingroup OTHERauxiliary
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*
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* =====================================================================
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DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
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*
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* -- LAPACK auxiliary routine --
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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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*
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* .. Scalar Arguments ..
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DOUBLE PRECISION X, Y
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D0 )
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DOUBLE PRECISION ONE
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PARAMETER ( ONE = 1.0D0 )
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* ..
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* .. Local Scalars ..
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DOUBLE PRECISION W, XABS, YABS, Z, HUGEVAL
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LOGICAL X_IS_NAN, Y_IS_NAN
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* ..
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* .. External Functions ..
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LOGICAL DISNAN
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EXTERNAL DISNAN
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* ..
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* .. External Subroutines ..
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DOUBLE PRECISION DLAMCH
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, MAX, MIN, SQRT
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* ..
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* .. Executable Statements ..
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*
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X_IS_NAN = DISNAN( X )
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Y_IS_NAN = DISNAN( Y )
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IF ( X_IS_NAN ) DLAPY2 = X
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IF ( Y_IS_NAN ) DLAPY2 = Y
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HUGEVAL = DLAMCH( 'Overflow' )
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*
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IF ( .NOT.( X_IS_NAN.OR.Y_IS_NAN ) ) THEN
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XABS = ABS( X )
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YABS = ABS( Y )
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W = MAX( XABS, YABS )
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Z = MIN( XABS, YABS )
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IF( Z.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
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DLAPY2 = W
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ELSE
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DLAPY2 = W*SQRT( ONE+( Z / W )**2 )
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END IF
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END IF
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RETURN
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*
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* End of DLAPY2
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*
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END
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