if xset == 0;
	xdata = linspace (-2, 2, ndata)';
elseif xset == 1;
	xdata = (sort((4.*(rand(ndata,1))-2)));
elseif xset ==2;
	xdata = sort(.7*(randn(ndata,1)));
elseif xset ==3;
	x = .5.*(1-(rand(floor(ndata/2),1).^.5));
	y = .75+ .125.*(randn(ceil(ndata/2),1));
	z = x;
	z(ceil(ndata/2):ndata) = y;
	z = 4.*z - 2;	
	xdata = sort(z);
end;
