idamax()

integer function idamax	(	integer	N,
		double precision, dimension(*)	DX,
		integer	INCX
	)

IDAMAX

Purpose:

    IDAMAX finds the index of the first element having maximum absolute value.

Parameters

[in]	N	N is INTEGER number of elements in input vector(s)
[in]	DX	DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
[in]	INCX	INCX is INTEGER storage spacing between elements of DX

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date

November 2017

Further Details:

     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(*)

Definition at line 73 of file idamax.f.

*
*  -- Reference BLAS level1 routine (version 3.8.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2017
*
*     .. Scalar Arguments ..
      INTEGER INCX,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DX(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION DMAX
      INTEGER I,IX
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC dabs
*     ..
      idamax = 0
      IF (n.LT.1 .OR. incx.LE.0) RETURN
      idamax = 1
      IF (n.EQ.1) RETURN
      IF (incx.EQ.1) THEN
*
*        code for increment equal to 1
*
         dmax = dabs(dx(1))
         DO i = 2,n
            IF (dabs(dx(i)).GT.dmax) THEN
               idamax = i
               dmax = dabs(dx(i))
            END IF
         END DO
      ELSE
*
*        code for increment not equal to 1
*
         ix = 1
         dmax = dabs(dx(1))
         ix = ix + incx
         DO i = 2,n
            IF (dabs(dx(ix)).GT.dmax) THEN
               idamax = i
               dmax = dabs(dx(ix))
            END IF
            ix = ix + incx
         END DO
      END IF
      RETURN

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