//clc()
disp("f(x,y) = 4*exp(0.8*x) - 0.5*y")
//f'(x,y) = 4*exp(0.8*x) - 0.5*y
x = 0:2:2;
y(1) = 2;
h =2;
t = 14.84392;
k1 = 4*exp(0.8*x(1)) - 0.5*y(1);
x1 = x(1) + h/2;
y1 = y(1) + k1*h/2;
k2 = 4*exp(0.8*x1) - 0.5*y1;
x1 = x(1) + h/2;
y1 = y(1) + k2*h/2;
k3 = 4*exp(0.8*x1) - 0.5*y1;
x1 = x(1) + h;
y1 = y(1) + k3*h;
k4 = 4*exp(0.8*x1) - 0.5*y1;
y(2) = y(1) + (k1 + 2*k2 + 2*k3 + k4)*h/6;
e = (t - y(2))/(t);
disp(y(1:2),"y by h = 2 is")
disp(e,"error = ")
h = 1;
x = 0:h:2;
for i=1:3
    k1(i) = 4*exp(0.8*x(i)) - 0.5*y(i);
    x1 = x(i) + h/2;
    y1 = y(i) + k1(i)*h/2;
    k2(i) = 4*exp(0.8*x1) - 0.5*y1;
    x1 = x(i) + h/2;
    y1 = y(i) + k2(i)*h/2;
    k3(i) = 4*exp(0.8*x1) - 0.5*y1;
    x1 = x(i) + h;
    y1 = y(i) + k3(i)*h;
    k4(i) = 4*exp(0.8*x1) - 0.5*y1;
    y(i+1) = y(i) + (k1(i) + 2*k2(i) + 2*k3(i) + k4(i))*h/6;    
end
e = (t - (y(3)))/t;
disp(y(1:3),"y by h = 1 is")
disp(e,"error = ")