127 lines
2.7 KiB
Fortran
127 lines
2.7 KiB
Fortran
*> \brief \b IDAMAX
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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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* Definition:
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* ===========
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*
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* INTEGER FUNCTION IDAMAX(N,DX,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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* DOUBLE PRECISION DX(*)
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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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*> IDAMAX finds the index of the first element having maximum 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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*> number of elements in input vector(s)
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*> \endverbatim
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*>
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*> \param[in] DX
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*> \verbatim
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*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
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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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*> storage spacing between elements of DX
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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 November 2017
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*
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*> \ingroup aux_blas
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> jack dongarra, linpack, 3/11/78.
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*> modified 3/93 to return if incx .le. 0.
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*> modified 12/3/93, array(1) declarations changed to array(*)
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*> \endverbatim
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*>
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* =====================================================================
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INTEGER FUNCTION IDAMAX(N,DX,INCX)
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*
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* -- Reference BLAS level1 routine (version 3.8.0) --
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* -- Reference BLAS 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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* November 2017
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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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DOUBLE PRECISION DX(*)
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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 DMAX
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INTEGER I,IX
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC DABS
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* ..
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IDAMAX = 0
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IF (N.LT.1 .OR. INCX.LE.0) RETURN
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IDAMAX = 1
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IF (N.EQ.1) RETURN
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IF (INCX.EQ.1) THEN
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*
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* code for increment equal to 1
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*
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DMAX = DABS(DX(1))
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DO I = 2,N
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IF (DABS(DX(I)).GT.DMAX) THEN
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IDAMAX = I
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DMAX = DABS(DX(I))
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END IF
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END DO
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ELSE
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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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DMAX = DABS(DX(1))
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IX = IX + INCX
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DO I = 2,N
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IF (DABS(DX(IX)).GT.DMAX) THEN
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IDAMAX = I
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DMAX = DABS(DX(IX))
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END IF
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IX = IX + INCX
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END DO
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END IF
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RETURN
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END
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