113 lines
2.8 KiB
Fortran
113 lines
2.8 KiB
Fortran
*> \brief \b DLAPY3 returns sqrt(x2+y2+z2).
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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 DLAPY3 + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy3.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/dlapy3.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/dlapy3.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 DLAPY3( X, Y, Z )
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION X, Y, Z
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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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*> DLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
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*> unnecessary 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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*> \endverbatim
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*>
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*> \param[in] Z
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*> \verbatim
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*> Z is DOUBLE PRECISION
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*> X, Y and Z specify the values x, y and z.
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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 DLAPY3( X, Y, Z )
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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, Z
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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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* ..
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* .. Local Scalars ..
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DOUBLE PRECISION W, XABS, YABS, ZABS, HUGEVAL
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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, SQRT
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* ..
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* .. Executable Statements ..
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*
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HUGEVAL = DLAMCH( 'Overflow' )
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XABS = ABS( X )
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YABS = ABS( Y )
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ZABS = ABS( Z )
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W = MAX( XABS, YABS, ZABS )
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IF( W.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
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* W can be zero for max(0,nan,0)
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* adding all three entries together will make sure
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* NaN will not disappear.
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DLAPY3 = XABS + YABS + ZABS
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ELSE
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DLAPY3 = W*SQRT( ( XABS / W )**2+( YABS / W )**2+
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$ ( ZABS / W )**2 )
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END IF
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RETURN
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*
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* End of DLAPY3
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*
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END
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