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|
*> \brief \b ISAMAX
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* INTEGER FUNCTION ISAMAX(N,SX,INCX)
*
* .. Scalar Arguments ..
* INTEGER INCX,N
* ..
* .. Array Arguments ..
* REAL SX(*)
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> ISAMAX finds the index of the first element having maximum absolute value.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in] SX
*> \verbatim
*> SX is REAL array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*> INCX is INTEGER
*> storage spacing between elements of SX
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup aux_blas
*
*> \par Further Details:
* =====================
*>
*> \verbatim
*>
*> jack dongarra, linpack, 3/11/78.
*> modified 3/93 to return if incx .le. 0.
*> modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
* =====================================================================
INTEGER FUNCTION ISAMAX(N,SX,INCX)
*
* -- Reference BLAS level1 routine (version 3.7.0) --
* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* December 2016
*
* .. Scalar Arguments ..
INTEGER INCX,N
* ..
* .. Array Arguments ..
REAL SX(*)
* ..
*
* =====================================================================
*
* .. Local Scalars ..
REAL SMAX
INTEGER I,IX
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS
* ..
ISAMAX = 0
IF (N.LT.1 .OR. INCX.LE.0) RETURN
ISAMAX = 1
IF (N.EQ.1) RETURN
IF (INCX.EQ.1) THEN
*
* code for increment equal to 1
*
SMAX = ABS(SX(1))
DO I = 2,N
IF (ABS(SX(I)).GT.SMAX) THEN
ISAMAX = I
SMAX = ABS(SX(I))
END IF
END DO
ELSE
*
* code for increment not equal to 1
*
IX = 1
SMAX = ABS(SX(1))
IX = IX + INCX
DO I = 2,N
IF (ABS(SX(IX)).GT.SMAX) THEN
ISAMAX = I
SMAX = ABS(SX(IX))
END IF
IX = IX + INCX
END DO
END IF
RETURN
END
|
