155 lines
3.6 KiB
Fortran
155 lines
3.6 KiB
Fortran
*> \brief \b IZMAX1 finds the index of the vector element whose real part has maximum absolute value.
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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 IZMAX1 + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/izmax1.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/izmax1.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/izmax1.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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* INTEGER FUNCTION IZMAX1( N, CX, INCX )
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*
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* .. Scalar Arguments ..
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* INTEGER INCX, N
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* ..
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* .. Array Arguments ..
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* COMPLEX*16 CX( * )
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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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*> IZMAX1 finds the index of the element whose real part has maximum
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*> absolute value.
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*>
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*> Based on IZAMAX from Level 1 BLAS.
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*> The change is to use the 'genuine' absolute value.
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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] N
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*> \verbatim
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*> N is INTEGER
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*> The number of elements in the vector CX.
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*> \endverbatim
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*>
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*> \param[in] CX
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*> \verbatim
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*> CX is COMPLEX*16 array, dimension (N)
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*> The vector whose elements will be summed.
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> The spacing between successive values of CX. INCX >= 1.
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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 complex16OTHERauxiliary
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*
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*> \par Contributors:
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* ==================
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*>
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*> Nick Higham for use with ZLACON.
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*
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* =====================================================================
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INTEGER FUNCTION IZMAX1( N, CX, INCX )
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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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INTEGER INCX, N
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* ..
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* .. Array Arguments ..
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COMPLEX*16 CX( * )
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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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INTEGER I, IX
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DOUBLE PRECISION SMAX
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COMPLEX*16 ZDUM
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS
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* ..
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* .. Statement Functions ..
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DOUBLE PRECISION CABS1
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* ..
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* .. Statement Function definitions ..
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*
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* NEXT LINE IS THE ONLY MODIFICATION.
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CABS1( ZDUM ) = ABS( ZDUM )
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* ..
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* .. Executable Statements ..
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*
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IZMAX1 = 0
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IF( N.LT.1 )
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$ RETURN
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IZMAX1 = 1
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IF( N.EQ.1 )
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$ RETURN
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IF( INCX.EQ.1 )
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$ GO TO 30
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*
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* CODE FOR INCREMENT NOT EQUAL TO 1
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*
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IX = 1
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SMAX = CABS1( CX( 1 ) )
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IX = IX + INCX
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DO 20 I = 2, N
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IF( CABS1( CX( IX ) ).LE.SMAX )
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$ GO TO 10
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IZMAX1 = I
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SMAX = CABS1( CX( IX ) )
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10 CONTINUE
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IX = IX + INCX
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20 CONTINUE
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RETURN
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*
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* CODE FOR INCREMENT EQUAL TO 1
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*
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30 CONTINUE
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SMAX = CABS1( CX( 1 ) )
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DO 40 I = 2, N
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IF( CABS1( CX( I ) ).LE.SMAX )
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$ GO TO 40
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IZMAX1 = I
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SMAX = CABS1( CX( I ) )
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40 CONTINUE
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RETURN
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*
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* End of IZMAX1
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*
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END
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