function [y1,y2,y3,y4]=diff(x,h)
y1=(f(x+h)-f(x-h))/(2*h);
y2=(f(x+h)-2*f(x)+f(x-h))/h^2;
y3=(f(x+2*h)-2*f(x+h)+2*f(x-h)-f(x-2*h))/(2*h^3);
y4=(f(x+2*h)-4*f(x+h)+6*f(x)-4*f(x-h)+f(x-2*h))/h^4;

