# Stability Experiments for Forward Euler¶

In [3]:
import numpy as np
import matplotlib.pyplot as pt


We'll integrate

$$y'=\alpha y$$

with $y'(0) = 1$,

using forward Euler.

Here are a few parameter settings that exhibit different situations that can occur:

In [22]:
#alpha = 1; h = 0.1; final_t = 20
#alpha = -1; h = 0.1; final_t = 20
#alpha = -1; h = 1; final_t = 20
alpha = -1; h = 1.5; final_t = 20
#alpha = -1; h = 2; final_t = 20
#alpha = -1; h = 2.5; final_t = 20


We specify the right-hand side and the initial condition:

In [23]:
t_values = [0]
y_values = [1]

def f(y):
return alpha * y


Integrate in time using Forward Euler:

In [24]:
while t_values[-1] < final_t:
t_values.append(t_values[-1] + h)
y_values.append(y_values[-1] + h*f(y_values[-1]))

In [ ]:
while t < t_final:
y = y + h * y * np.sin(3*t)
t += h



And plot:

In [25]:
mesh = np.linspace(0, final_t, 100)
pt.plot(t_values, y_values)
pt.plot(mesh, np.exp(alpha*mesh), label="true")
pt.legend()

Out[25]:
<matplotlib.legend.Legend at 0x11efe9fd0>
In [27]:
mesh = np.linspace(0, final_t, 15)
pt.plot(mesh, y_values-np.exp(alpha*mesh), label="true")
pt.legend()

Out[27]:
<matplotlib.legend.Legend at 0x11f03d750>