izmax1.c

来自「SuperLU is a general purpose library for」· C语言 代码 · 共 114 行

/*! @file izmax1.c
 * \brief Finds the index of the element whose real part has maximum absolute value
 *
 * <pre>
 *     -- LAPACK auxiliary routine (version 2.0) --   
 *     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
 *     Courant Institute, Argonne National Lab, and Rice University   
 *     October 31, 1992   
 * </pre>
 */
#include <math.h>
#include "slu_dcomplex.h"
#include "slu_Cnames.h"

/*! \brief 

<pre>
    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) INT   
            The number of elements in the vector CX.   

    CX      (input) COMPLEX*16 array, dimension (N)   
            The vector whose elements will be summed.   

    INCX    (input) INT   
            The spacing between successive values of CX.  INCX >= 1.   

   ===================================================================== 
</pre>
*/  

int
izmax1_(int *n, doublecomplex *cx, int *incx)
{


    /* System generated locals */
    int ret_val, i__1, i__2;
    double d__1;
    
    /* Local variables */
    double smax;
    int i, ix;

#define CX(I) cx[(I)-1]

    ret_val = 0;
    if (*n < 1) {
	return ret_val;
    }
    ret_val = 1;
    if (*n == 1) {
	return ret_val;
    }
    if (*incx == 1) {
	goto L30;
    }

/*     CODE FOR INCREMENT NOT EQUAL TO 1 */

    ix = 1;
    smax = (d__1 = CX(1).r, fabs(d__1));
    ix += *incx;
    i__1 = *n;
    for (i = 2; i <= *n; ++i) {
	i__2 = ix;
	if ((d__1 = CX(ix).r, fabs(d__1)) <= smax) {
	    goto L10;
	}
	ret_val = i;
	i__2 = ix;
	smax = (d__1 = CX(ix).r, fabs(d__1));
L10:
	ix += *incx;
/* L20: */
    }
    return ret_val;

/*     CODE FOR INCREMENT EQUAL TO 1 */

L30:
    smax = (d__1 = CX(1).r, fabs(d__1));
    i__1 = *n;
    for (i = 2; i <= *n; ++i) {
	i__2 = i;
	if ((d__1 = CX(i).r, fabs(d__1)) <= smax) {
	    goto L40;
	}
	ret_val = i;
	i__2 = i;
	smax = (d__1 = CX(i).r, fabs(d__1));
L40:
	;
    }
    return ret_val;

/*     End of IZMAX1 */

} /* izmax1_ */