Display two Sympy plots as two Matplotlib subplots

问题

This code

from sympy import *
x=Symbol('x')
p1 = plot(x**2,(x,-2,2))
p2 = plot(x**3,(x,-2,2))

results in two separate plots.

Instead of two separate plots, I want to display them with matplotlib as subplots:

import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)
plt.show()

How can I add p1 and p2, so that they are displayed as subplots inside the matplotlib figure?

回答1:

The problem is that sympy Plot creates its own figure and axes. It is not meant to draw to an existing axes.

You may however replace the axes the plot is drawn to by an existing axes prior to showing the sympy plot.

from sympy import Symbol,plot
import matplotlib.pyplot as plt

def move_sympyplot_to_axes(p, ax):
    backend = p.backend(p)
    backend.ax = ax
    backend.process_series()
    backend.ax.spines['right'].set_color('none')
    backend.ax.spines['bottom'].set_position('zero')
    backend.ax.spines['top'].set_color('none')
    plt.close(backend.fig)


x=Symbol('x')
p1 = plot(x**2,(x,-2,2), show=False)
p2 = plot(x**3,(x,-2,2), show=False)


fig, (ax,ax2) = plt.subplots(ncols=2)
move_sympyplot_to_axes(p1, ax)
move_sympyplot_to_axes(p2, ax2)

plt.show()

回答2:

My solution does not add p1, p2 to the subplots directly. But (x,y) coordinates from them are captured and used instead.

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

from sympy import symbols
from sympy.plotting import plot

# part 1
# uses symbolic plot of functions
x = symbols('x')

#p1, p2 = plot(x**2, x**3, (x, -2, 2))

# this plot will not show ...
# only produce 2 curves
p1, p2 = plot((x**2, (x, -2, 2)), \
                (x**3, (x, -2, 2)), \
                show=False)

# collect (x,y)'s of the unseen curves 
x1y1 = p1.get_points()  # array of 2D
x2y2 = p2.get_points() 

# part 2
# uses regular matplotlib to plot the data

fig = plt.figure(figsize=(8, 5))
ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)

# do subplot 1 
ax1.plot(x1y1[0], x1y1[1], 'g')  # plot x**2 in green
ax1.set_xlim([-2, 2])
ax1.set_xlabel('X1')
ax1.set_ylabel('Y1')
ax1.set_title('Line1')  # destroyed by another .title(); axis metho1

# do subplot 2
ax2.plot(x2y2[0], x2y2[1], 'r')  # plot x**3 in red
ax2.set_xlim([-2, 2])
ax2.set_xlabel('X2')
ax2.set_ylabel('Y2')
ax2.set_title('Line2')

fig.subplots_adjust(wspace=0.4) # set space between subplots

plt.show()

The resulting plot:

来源：https://stackoverflow.com/questions/46810880/display-two-sympy-plots-as-two-matplotlib-subplots

标签

matplotlib

sympy