Updating a matrix plot in matplotlib during for cycle

Question

I am running a simulation and I need to update a plot of a matrix every iteration (or every n iterations for that matter). I am doing the plotting using matplotlib, in particular matshow. I tried replicating the code I saw in other StackOverflow questions but I haven't been successful. Currently the code just produces different windows with the new plots instead of updating the first one. Here's the code so far:

import numpy as np
import random
import math
import matplotlib.pyplot as plt
import matplotlib.animation as anim

#   System variables initialization
N = 50
n_iter = 5
betaJ = 0.40
lattice = np.ones([N, N])
energy = -2*betaJ*N**2
choices = list(range(N))

plt.ion()
fig = plt.figure()

#   Main cycle
for i in range(0, n_iter):
    #   Pick random spin and calculate energy variation caused by flipping it
    x, y = random.choice(choices), random.choice(choices)
    neighbour_spin_sum = lattice[np.mod(x-1, N), y] + lattice[np.mod(x+1, N), y] + lattice[x, np.mod(y+1, N)] + lattice[x, np.mod(y-1, N)]
    delta_energy = 2*betaJ*(neighbour_spin_sum*lattice[x, y])

    #   If energetically favorable, flip spin
    if delta_energy < 0:
        lattice[x, y] = -lattice[x, y] 

    #   Else flip with some probability
    elif random.uniform(0, 1) <= math.exp(-delta_energy):
        lattice[x, y] = -lattice[x, y] 

    plt.matshow(lattice)
    plt.draw()
    plt.pause(0.0001)

Thanks!

I highly suggest you change n_iter to something more reasonable for this code, else unsuspecting people running this will get 10,000 new windows opened. — zephyr
– zephyr, Commented Mar 3, 2016 at 20:00
Not a solution to your question directly, but you can try other plotting methods that don't require using matshow. imshow might be close to what you're looking for. — zephyr
– zephyr, Commented Mar 3, 2016 at 20:36

veda905 · Accepted Answer · 2016-03-03 20:01:24Z

2

The issue is that every time the plt.matshow() is called matplotlib creates a new plotting axis. To get around this, define the axis and keep reusing it as shown below:

import numpy as np
import random
import math
import matplotlib.pyplot as plt
import matplotlib.animation as anim

#   System variables initialization
N = 50
n_iter = 10000
betaJ = 0.40
lattice = np.ones([N, N])
energy = -2 * betaJ * N ** 2
choices = list(range(N))

plt.ion()
fig = plt.figure()

#   Main cycle
for i in range(0, n_iter):
    #   Pick random spin and calculate energy variation caused by flipping it
    x = random.choice(choices)
    y = random.choice(choices)
    neighbour_spin_sum = lattice[np.mod(x-1, N), y] + lattice[np.mod(x+1, N), y] + lattice[x, np.mod(y+1, N)] + lattice[x, np.mod(y-1, N)]

    delta_energy = 2*betaJ*(neighbour_spin_sum*lattice[x, y])

    #   If energetically favorable, flip spin
    if delta_energy < 0:
        lattice[x, y] = -lattice[x, y] 

    #   Else flip with some probability
    elif random.uniform(0, 1) <= math.exp(-delta_energy):
        lattice[x, y] = -lattice[x, y] 

    ax = fig.add_subplot(111)
    ax.matshow(lattice)
    plt.draw()
    plt.pause(0.0001)

answered Mar 3, 2016 at 20:01

veda905

7722 gold badges14 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user3930598 Over a year ago

Thanks for the reply! This seems to only work on python 2, any idea why?

veda905 Over a year ago

It works for me in python 2.7.11 and 3.4.2 (which is a little out of date) Which version specifically are you looking to use it with?

Collectives™ on Stack Overflow

Updating a matrix plot in matplotlib during for cycle

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related