*> \brief \b IDAMAX * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * INTEGER FUNCTION IDAMAX(N,DX,INCX) * * .. Scalar Arguments .. * INTEGER INCX,N * .. * .. Array Arguments .. * DOUBLE PRECISION DX(*) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> IDAMAX 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] DX *> \verbatim *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) ) *> \endverbatim *> *> \param[in] INCX *> \verbatim *> INCX is INTEGER *> storage spacing between elements of DX *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date November 2017 * *> \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 IDAMAX(N,DX,INCX) * * -- 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 END