Created
September 13, 2018 17:42
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Euler's Method for solving Differential Equations
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def parse_location(s: str): | |
if s.startswith("(") and s.endswith(")"): | |
parts = s[1:-1].split(',') | |
if len(parts) == 2: | |
try: | |
return tuple(map(int, parts)) | |
except ValueError: | |
pass | |
raise ValueError(f"Invalid location: {s!r}") | |
def eulers_method(): | |
equation_code = input("Differential Equation? ").strip() | |
equation = compile(equation_code, '<equation>', 'eval') | |
start = parse_location(input("Initial condition? ")) | |
step = float(input("Approximation step? ")) | |
end = float(input("Ending value of x? ")) | |
def run_equation(x, y): | |
return eval(equation, globals(), {"x": x, "y": y}) | |
print() | |
print(f"Approximating dy/dx = `{equation_code}` with initial condition {start} and step {step}") | |
start_derivative = run_equation(*start) | |
start_delta_y = start_derivative * step | |
table = [(start, start_derivative, start_delta_y)] | |
while abs(table[-1][0][0]) < abs(end): | |
(x_old, y_old), derivative_old, delta_y_old = table[-1] | |
updated_location = (x_old + step, y_old + delta_y_old) | |
updated_derivative = run_equation(*updated_location) | |
updated_delta_y = updated_derivative * step | |
table.append((updated_location, updated_derivative, updated_delta_y)) | |
# Print a nice-markdown style table | |
print("| x | y | dy/dx | \u0394y |") | |
print("|-------|---------|-----------|--------|") | |
for (x, y), derivative, delta_y in table: | |
digits = 4 | |
x = round(x, digits) | |
y = round(y, digits) | |
derivative = round(derivative, digits) | |
delta_y = round(delta_y, digits) | |
print(f"|{x: < 7}|{y: < 9}|{derivative: < 11}|{delta_y: < 8}|") | |
if __name__ == "__main__": | |
while True: | |
eulers_method() | |
if input("Do you want to continue [Y/n]?").lower() in ("no", "n"): | |
break |
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