Python Classical RK4 ODE Solver for System of Two Ordinary Differential Equations

Mathematical calculations: https://math.stackexchange.com/questions/721076/

x'(t) = x(t) - y(t) + 2t - t^2 - t^3
y'(t) = x(t) + y(t) - 4t^2 + t^3

With the initial conditions
x(0) = 1
y(0) = 0
t in [0,1]

x(t) = e^t * cos(t) + t^2
y(t) = e^t * sin(t) - t^3

Using currently built-in ODEs and their solutions