izmax1.f

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*> \brief \b IZMAX1 finds the index of the first vector element of maximum absolute value.
*
*  =========== DOCUMENTATION ===========
*
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*
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*
*  Definition:
*  ===========
*
*       INTEGER          FUNCTION IZMAX1( N, ZX, INCX )
*
*       .. Scalar Arguments ..
*       INTEGER            INCX, N
*       ..
*       .. Array Arguments ..
*       COMPLEX*16         ZX( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> IZMAX1 finds the index of the first vector element of maximum absolute value.
*>
*> Based on IZAMAX from Level 1 BLAS.
*> The change is to use the 'genuine' absolute value.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of elements in the vector ZX.
*> \endverbatim
*>
*> \param[in] ZX
*> \verbatim
*>          ZX is COMPLEX*16 array, dimension (N)
*>          The vector ZX. The IZMAX1 function returns the index of its first
*>          element of maximum absolute value.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>          The spacing between successive values of ZX.  INCX >= 1.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup imax1
*
*> \par Contributors:
*  ==================
*>
*> Nick Higham for use with ZLACON.
*
*  =====================================================================
      INTEGER FUNCTION izmax1( N, ZX, INCX )
*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER            incx, n
*     ..
*     .. Array Arguments ..
      COMPLEX*16         zx(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION   dmax
      INTEGER            i, ix
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs
*     ..
*     .. Executable Statements ..
*
      izmax1 = 0
      IF (n.LT.1 .OR. incx.LE.0) RETURN
      izmax1 = 1
      IF (n.EQ.1) RETURN
      IF (incx.EQ.1) THEN
*
*        code for increment equal to 1
*
         dmax = abs(zx(1))
         DO i = 2,n
            IF (abs(zx(i)).GT.dmax) THEN
               izmax1 = i
               dmax = abs(zx(i))
            END IF
         END DO
      ELSE
*
*        code for increment not equal to 1
*
         ix = 1
         dmax = abs(zx(1))
         ix = ix + incx
         DO i = 2,n
            IF (abs(zx(ix)).GT.dmax) THEN
               izmax1 = i
               dmax = abs(zx(ix))
            END IF
            ix = ix + incx
         END DO
      END IF
      RETURN
*
*     End of IZMAX1
*
      END