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18 changes: 10 additions & 8 deletions maths/rkf45.py → maths/runge_kutta_fehlberg_45.py
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@
import numpy as np


def runge_futta_fehlberg_45(
def runge_kutta_fehlberg_45(
func: Callable,
x_initial: float,
y_initial: float,
Expand All @@ -33,33 +33,35 @@ def runge_futta_fehlberg_45(
# exact value of y[1] is tan(0.2) = 0.2027100937470787
>>> def f(x, y):
... return 1 + y**2
>>> y = runge_futta_fehlberg_45(f, 0, 0, 0.2, 1)
>>> y = runge_kutta_fehlberg_45(f, 0, 0, 0.2, 1)
>>> y[1]
0.2027100937470787
>>> def f(x,y):
... return x
>>> y = runge_futta_fehlberg_45(f, -1, 0, 0.2, 0)
>>> y = runge_kutta_fehlberg_45(f, -1, 0, 0.2, 0)
>>> y[1]
-0.18000000000000002
>>> y = runge_futta_fehlberg_45(5, 0, 0, 0.1, 1)
>>> y = runge_kutta_fehlberg_45(5, 0, 0, 0.1, 1)
Traceback (most recent call last):
...
TypeError: 'int' object is not callable
>>> def f(x, y):
... return x + y
>>> y = runge_futta_fehlberg_45(f, 0, 0, 0.2, -1)
>>> y = runge_kutta_fehlberg_45(f, 0, 0, 0.2, -1)
Traceback (most recent call last):
...
ValueError: The final value x must be greater than initial value of x.
ValueError: The final value of x must be greater than initial value of x.
>>> def f(x, y):
... return x
>>> y = runge_futta_fehlberg_45(f, -1, 0, -0.2, 0)
>>> y = runge_kutta_fehlberg_45(f, -1, 0, -0.2, 0)
Traceback (most recent call last):
...
ValueError: Step size must be positive.
"""
if x_initial >= x_final:
raise ValueError("The final value x must be greater than initial value of x.")
raise ValueError(
"The final value of x must be greater than initial value of x."
)

if step_size <= 0:
raise ValueError("Step size must be positive.")
Expand Down