izmax1.c

来自「InsightToolkit-1.4.0(有大量的优化算法程序)」· C语言 代码 · 共 79 行

#include "f2c.h"
#include "netlib.h"

integer izmax1_(n, cx, incx)
const integer *n;
const doublecomplex *cx;
const integer *incx;
{
    /* System generated locals */
    integer ret_val = 0;

    /* Local variables */
    static doublereal smax;
    static integer i, ix;


/*  -- LAPACK auxiliary routine (version 2.0) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/*     Courant Institute, Argonne National Lab, and Rice University */
/*     September 30, 1994 */

/*  Purpose                                                             */
/*  =======                                                             */
/*                                                                      */
/*  IZMAX1 finds the index of the element whose real part has maximum   */
/*  absolute value.                                                     */
/*                                                                      */
/*  Based on IZAMAX from Level 1 BLAS.                                  */
/*  The change is to use the 'genuine' absolute value.                  */
/*                                                                      */
/*  Contributed by Nick Higham for use with ZLACON.                     */
/*                                                                      */
/*  Arguments                                                           */
/*  =========                                                           */
/*                                                                      */
/*  N       (input) INTEGER                                             */
/*          The number of elements in the vector CX.                    */
/*                                                                      */
/*  CX      (input) COMPLEX*16 array, dimension (N)                     */
/*          The vector whose elements will be summed.                   */
/*                                                                      */
/*  INCX    (input) INTEGER                                             */
/*          The spacing between successive values of CX.  INCX >= 1.    */
/*                                                                      */
/* =====================================================================*/

    if (*n < 1) {
        return 0;
    }
    if (*n == 1) {
        return 1;
    }
/*     CODE FOR INCREMENT EQUAL TO 1 */
    if (*incx == 1) {
        smax = abs(cx[0].r);
        for (i = 1; i < *n; ++i) {
            if (abs(cx[i].r) > smax) {
                ret_val = i+1;
                smax = abs(cx[i].r);
            }
        }
    }

/*     CODE FOR INCREMENT NOT EQUAL TO 1 */
    else {
        ix = 0;
        smax = abs(cx[0].r);
        ix += *incx;
        for (i = 1; i < *n; ++i, ix += *incx) {
            if (abs(cx[ix].r) > smax) {
                ret_val = i+1;
                smax = abs(cx[ix].r);
            }
        }
    }
    return ret_val;

} /* izmax1_ */