如何将 sympy 表达式转换为图形？

Question

How do I convert the following equation, as a function of f_ q (which is a function of 2D-vector q ) into a graphical representation?

It may be easier to consider something like y = sin(x) for the explanation however

Answer 1

I think you need to install matplotlib but then you should be able to do

>>> plot(x**2 + 1)

For your example you would have to give values for all parameters in order to see a plot wrt q, eg

>>> plot(omega_q.subs([(omega0, 1), (Omega,2)]))

See the documentation on plotting in the doc/src/modules/plotting.rst

Answer 2

Sympy has it's own plotting module . This module is mostly for convenience, to rapidly view a function without the need to leave sympy. There are very limited options for formatting.

Plotting y=sin(x) is just:

from sympy import plot, sin
from sympy.abc import x
plot(sin(x))

But that is only for 1D functions. To plot 2D functions, matplotlib is the go-to library. The simplest would be a 2D plot using color as a 3dimension. Nicer and more informative plots can be got from 3D plots. Matplotlib standardly allows interacting with them to be viewed from different directions.

Here is an example:

from sympy import sin, lambdify
from sympy.abc import x, y, a, b

f = sin(a*x*y+b) / (x*x+y*y+1)
# convert to a numpy function, make sure all variables apart from x and y have a fixed value
f_np = lambdify((x,y), f.subs({a: 1.5, b: 1}), 'numpy')


from matplotlib import pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
import numpy as np

x, y = np.meshgrid(np.linspace(-2,2,100), np.linspace(-2,2,100))
z = f_np(x, y)

fig = plt.figure()
ax = plt.axes(projection="3d")
ax.plot_surface(x, y, z, edgecolor='none', cmap='terrain')

plt.show()

See this interesting site for more ideas about 3d plotting.