get_min.c

来自「speech signal process tools」· C语言 代码 · 共 65 行

/*
Given the range xmin to xmax and the number of points N on the range
( including the end points ) and the function name for computing the
value of the function, find the minimum value of the function and the
x that produces that minimum.
Assume only one minimum in range and no maxima except at the ends of the range.
*/
get_min(xmin,xmax,N,function,min_x,min_y,level,flag)
int N,level,flag;
double xmin,xmax,*min_x,*min_y;
double (*function)();
{
	double x,del_x,y;
	double new_xmin,new_xmax;
	double n_min_x,n_min_y;
	int i,s_i;

	del_x=(xmax-xmin)/(N-1);
	*min_y= 1e30;
	for(i=0;i<N;i++)
		{
		x=xmin+i*del_x;
		y=(*function)(x);
		printf("x=%g y=%g\n",x,y);
		if(*min_y>y)
			{
			/* function decreasing */
			*min_y=y;
			*min_x=x;
			s_i=i;/* save position in table of minimum */
			}
		else
			{
			if(i && !flag)
				/* function increasing */
				break;
			}
		}
	if(level>1)
		{
		if(s_i==0)
			{
			new_xmin=xmin;
			new_xmax=xmin+del_x;
			}
		else if(s_i==(N-1))
			{
			new_xmin=xmax-del_x;
			new_xmax=xmax;
			}
		else
			{
			new_xmin=xmin+(s_i-1)*del_x;
			new_xmax=xmin+(s_i+1)*del_x;
			}
	get_min(new_xmin,new_xmax,N,function,&n_min_x,&n_min_y,level-1,flag);
		if(n_min_y<*min_y)
			{
			*min_y=n_min_y;
			*min_x=n_min_x;
			}
		}
	return;
}