Question

我需要绘制DE方程，但是我不知道该怎么做。

首先，解决问题。

#10527113
from sympy import *
import numpy as np
import matplotlib.pyplot as plt

# Solve the DE: 3y'' + 2y' +y = 0
x = symbols('x')
y = symbols('y', cls=Function)
diffeq1 = Eq(3*y(x).diff(x,x) + 2*y(x).diff(x) + y(x), 0)
ans1 = dsolve ( diffeq1, y(x) )
print ( ans1 )

然后是绘图部分。

#plotting
#Let x : [0, 2*pi], c1 = 1 and c2 = 0
b = []
a = np.linspace( 0, 2*np.pi )
for k in a:
    b.append(ans1.subs(x, k))

plt.plot(a, b, label="curve")

我在代码中输入了正确的'ans1'，但无法成功绘制。

Answer 1

绘图时，您在注释中说c1 = 1和c2 = 0，但没有在DE解算ans1中进行设置。我在您的代码中添加了替换内容，并选择了绘图解决方案的评估值。

from sympy import *
import numpy as np
import matplotlib.pyplot as plt

# Solve the DE: 3y'' + 2y' +y = 0
from sympy.solvers.ode import classify_sysode

x = symbols('x')
y = symbols('y', cls=Function)
diffeq1 = Eq(3*y(x).diff(x,x) + 2*y(x).diff(x) + y(x), 0)
ans1 = dsolve ( diffeq1, y(x) )
print ( ans1 )
# Eq(y(x), (C1*sin(sqrt(2)*x/3) + C2*cos(sqrt(2)*x/3))/exp(x)**(1/3))

print (ans1)

#plotting
# Let x : [0, 2*pi], c1 = 1 and c2 = 0
c1 = symbols('C1')
c2 = symbols('C2')
ans1 = ans1.subs(c1, 1) # substitute for c1
ans1 = ans1.subs(c2, 0) # substitute for c2
b = []
a = np.linspace( 0, 2*np.pi )
for k in a:
    sol = ans1.subs(x, k)
    b.append(sol.rhs) # select the value for plotting

plt.plot(a, b, label="curve")
plt.show()

如何绘制DE方程式？

1 个答案: