numpy - Slow and smooth drawing lines python matplotlib

Question

I'm using matplotlib for drawing graphs such as smooth lines. it is not problem to draw for me, but I have problems with animations.

import numpy as np
import random as random
from matplotlib import pyplot as plt
from matplotlib import animation

So, i have array, such as:

a = [0,1,2,4,5,8,9,12,14,18,22,17,30,37,29,45]

And I need to draw it smooth point-to-point. Now I have this strings:

for i in range(len(a)-1):
    desty = np.append(desty,np.linspace(a[i],a[i+1],n))
    destx = np.append(destx,np.linspace(i,i+1,n))

that allows me to draw lines without problems (and animations :))

the full code:

# First set up the figure, the axis, and the plot element we want to animate
fig = plt.figure()
ax = plt.axes(xlim=(0, 50), ylim=(0, 50))
line, = ax.plot([], [], lw=2)
global x
global y
global n
global a
n=5
a = [0,1,2,4,5,8,9,12,14,18,22,17,30,37,29,45]

global desty,destx
desty = np.linspace(0,0,n)
destx = np.linspace(0,0,n)
for i in range(len(a)-1):
    desty = np.append(desty,np.linspace(a[i],a[i+1],n))
    destx = np.append(destx,np.linspace(i,i+1,n))
# initialization function: plot the background of each frame
def init():
    line.set_data([], [])
    return line,
# animation function.  This is called sequentially
def animate(i):
    global destx
    global desty
    x=destx
    y=desty
    line.set_data(x, y)
    return line,

# call the animator.  blit=True means only re-draw the parts that have changed.
anim = animation.FuncAnimation(fig, animate, init_func=init,
                               frames=200, interval=20, blit=True)
plt.show()

Allows me to draw it only, but how can i draw it slow and smooth point to point?

I'm using python 2.7, centos 7.

Answer 1

You can slim your plotting routine down to:

import numpy as np
import random as random
from matplotlib import pyplot as plt
from matplotlib import animation
# First set up the figure, the axis, and the plot element we want to animate
fig = plt.figure()
ax = plt.axes(xlim=(0, 50), ylim=(0, 50))
line, = ax.plot([], [], lw=2)

n=5
a = [0,1,2,4,5,8,9,12,14,18,22,17,30,37,29,45]

x = []
y = []

# initialization function: plot the background of each frame
def init():
    line.set_data([], [])
    return line,

# animation function.  This is called sequentially
def animate(i):
    x.append(np.linspace(i,i+1,n))
    y.append(np.linspace(a[i],a[i+1],n))
    line.set_data(x,y)

    return line,

# call the animator.  blit=True means only re-draw the parts that have changed.
anim = animation.FuncAnimation(fig, animate, np.arange(0,len(a)-1) ,init_func=init, 
                               interval=200, blit=True, repeat=False)

plt.show()

Things to note:

• You don't require global variables for this to work
• You don't want to set up x and y outside of the animation but inside for the plot to develop (in your case you had the complete x and y set up so that the animation would only plot the entire graph)
• You need to pass an interable to animate (the i); this is the third input to FuncAnimation - np.arange(0,len(a)-1).
• set repeat=False to stop after one run and to avoid 'closing' the curve
• I increased interval to make the plot develop slower