107 lines
2.3 KiB
Fortran
107 lines
2.3 KiB
Fortran
*> \brief \b ISAMAX
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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 ISAMAX(N,SX,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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* REAL SX(*)
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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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*> ISAMAX finds the index of the first element having maximum absolute value.
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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 2015
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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 ISAMAX(N,SX,INCX)
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*
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* -- Reference BLAS level1 routine (version 3.6.0) --
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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 2015
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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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REAL SX(*)
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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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REAL SMAX
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INTEGER I,IX
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS
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* ..
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ISAMAX = 0
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IF (N.LT.1 .OR. INCX.LE.0) RETURN
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ISAMAX = 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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SMAX = ABS(SX(1))
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DO I = 2,N
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IF (ABS(SX(I)).GT.SMAX) THEN
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ISAMAX = I
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SMAX = ABS(SX(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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SMAX = ABS(SX(1))
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IX = IX + INCX
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DO I = 2,N
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IF (ABS(SX(IX)).GT.SMAX) THEN
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ISAMAX = I
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SMAX = ABS(SX(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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