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    1: *> \brief \b IDAMAX
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *  Definition:
    9: *  ===========
   10: *
   11: *       INTEGER FUNCTION IDAMAX(N,DX,INCX)
   12: *
   13: *       .. Scalar Arguments ..
   14: *       INTEGER INCX,N
   15: *       ..
   16: *       .. Array Arguments ..
   17: *       DOUBLE PRECISION DX(*)
   18: *       ..
   19: *
   20: *
   21: *> \par Purpose:
   22: *  =============
   23: *>
   24: *> \verbatim
   25: *>
   26: *>    IDAMAX finds the index of the first element having maximum absolute value.
   27: *> \endverbatim
   28: *
   29: *  Arguments:
   30: *  ==========
   31: *
   32: *> \param[in] N
   33: *> \verbatim
   34: *>          N is INTEGER
   35: *>         number of elements in input vector(s)
   36: *> \endverbatim
   37: *>
   38: *> \param[in] DX
   39: *> \verbatim
   40: *>          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
   41: *> \endverbatim
   42: *>
   43: *> \param[in] INCX
   44: *> \verbatim
   45: *>          INCX is INTEGER
   46: *>         storage spacing between elements of SX
   47: *> \endverbatim
   48: *
   49: *  Authors:
   50: *  ========
   51: *
   52: *> \author Univ. of Tennessee
   53: *> \author Univ. of California Berkeley
   54: *> \author Univ. of Colorado Denver
   55: *> \author NAG Ltd.
   56: *
   57: *> \date November 2017
   58: *
   59: *> \ingroup aux_blas
   60: *
   61: *> \par Further Details:
   62: *  =====================
   63: *>
   64: *> \verbatim
   65: *>
   66: *>     jack dongarra, linpack, 3/11/78.
   67: *>     modified 3/93 to return if incx .le. 0.
   68: *>     modified 12/3/93, array(1) declarations changed to array(*)
   69: *> \endverbatim
   70: *>
   71: *  =====================================================================
   72:       INTEGER FUNCTION IDAMAX(N,DX,INCX)
   73: *
   74: *  -- Reference BLAS level1 routine (version 3.8.0) --
   75: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   76: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   77: *     November 2017
   78: *
   79: *     .. Scalar Arguments ..
   80:       INTEGER INCX,N
   81: *     ..
   82: *     .. Array Arguments ..
   83:       DOUBLE PRECISION DX(*)
   84: *     ..
   85: *
   86: *  =====================================================================
   87: *
   88: *     .. Local Scalars ..
   89:       DOUBLE PRECISION DMAX
   90:       INTEGER I,IX
   91: *     ..
   92: *     .. Intrinsic Functions ..
   93:       INTRINSIC DABS
   94: *     ..
   95:       IDAMAX = 0
   96:       IF (N.LT.1 .OR. INCX.LE.0) RETURN
   97:       IDAMAX = 1
   98:       IF (N.EQ.1) RETURN
   99:       IF (INCX.EQ.1) THEN
  100: *
  101: *        code for increment equal to 1
  102: *
  103:          DMAX = DABS(DX(1))
  104:          DO I = 2,N
  105:             IF (DABS(DX(I)).GT.DMAX) THEN
  106:                IDAMAX = I
  107:                DMAX = DABS(DX(I))
  108:             END IF
  109:          END DO
  110:       ELSE
  111: *
  112: *        code for increment not equal to 1
  113: *
  114:          IX = 1
  115:          DMAX = DABS(DX(1))
  116:          IX = IX + INCX
  117:          DO I = 2,N
  118:             IF (DABS(DX(IX)).GT.DMAX) THEN
  119:                IDAMAX = I
  120:                DMAX = DABS(DX(IX))
  121:             END IF
  122:             IX = IX + INCX
  123:          END DO
  124:       END IF
  125:       RETURN
  126:       END