Hello I need to plot this simple system: x'' = -x using midpoint Euler. u1 = -x , u2 = -x' u1' = u2 u2' = -x u1(n+1) = u1(n) + h*? u2(n+1) = u2(n) + h*f((1/2)*(u1(n) + u1(n+1)) We dont know u1(n+1). I tried approximating it with u1(n+1) = u1(n) + h*u2(n) u2(1+i) = u2(i) + h * ((-1/2) * (u1(n) + u1(n+1)) Then we have u2(i+1) and u2(i). A midpoint value is (u2(1+i) - u(i))/2 u1(q+i) = u1(i) + h*midpoint When i plot this the result is some awful diverging line, not an oscillating function. What is wrong?