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ODE Examples in Sympy
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| import sympy as sym | |
| import numpy as np | |
| import matplotlib.pyplot as plt | |
| sym.init_printing() | |
| # Integral calculation constants | |
| a = 0 | |
| b = 20 | |
| h = 0.4 | |
| # Variables | |
| t = sym.symbols('t') | |
| y = sym.Function('y') | |
| # Initial conditions | |
| ics = {y(0): 1} | |
| # Equation hands | |
| left_hand = sym.Derivative(y(t), t) | |
| right_hand = -5 * y(t) | |
| eq = sym.Eq(left_hand, right_hand) | |
| print(sym.pretty(eq)) | |
| # Solve equation | |
| sol = sym.dsolve(eq, y(t), ics=ics) | |
| print(sym.pretty(sol)) | |
| # Transform into function | |
| fun_y = sym.lambdify(t, sol.rhs, modules=['numpy']) | |
| print(fun_y(0), fun_y(1)) | |
| # Séries de données | |
| t = np.arange(a, b + h, h) | |
| y = fun_y(t) | |
| print(t, y) | |
| # Graphique de y(t) | |
| plt.plot(t, y, color='b') | |
| plt.xlim(0, 20) | |
| plt.show() | |
| # ================================== Ex 2 | |
| x = sym.var('x') | |
| f = sym.Function('f') | |
| diffeq = sym.Eq(sym.Derivative(f(x), x), x + f(x) / 5) | |
| ics = {f(0): -3} | |
| sol2 = sym.dsolve(diffeq, f(x), ics=ics).rhs | |
| print(sym.pretty(sym.simplify(sol2))) | |
| # ================================== Ex 3 | |
| f_2 = sym.Function('f_2') | |
| x_2 = sym.var('x_2') | |
| A = sym.var("A") | |
| ics = {f_2(0): A} | |
| sol3 = sym.dsolve(f_2(x_2).diff(x_2) - f_2(x_2), f_2(x_2), ics=ics) | |
| print(sym.pretty(sol3)) |
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