Merge pull request matplotlib#19941 from timhoffm/doc-random-walk

Simplify 3D random walk example

Author: QuLogic

examples/animation/random_walk.py

@@ -13,62 +13,40 @@
 np.random.seed(19680801)
 
 
-def gen_rand_line(length, dims=2):
-    """
-    Create a line using a random walk algorithm.
+def random_walk(num_steps, max_step=0.05):
+    """Return a 3D random walk as (num_steps, 3) array."""
+    start_pos = np.random.random(3)
+    steps = np.random.uniform(-max_step, max_step, size=(num_steps, 3))
+    walk = start_pos + np.cumsum(steps, axis=0)
+    return walk
 
-    Parameters
-    ----------
-    length : int
-        The number of points of the line.
-    dims : int
-        The number of dimensions of the line.
-    """
-    line_data = np.empty((dims, length))
-    line_data[:, 0] = np.random.rand(dims)
-    for index in range(1, length):
-        # scaling the random numbers by 0.1 so
-        # movement is small compared to position.
-        # subtraction by 0.5 is to change the range to [-0.5, 0.5]
-        # to allow a line to move backwards.
-        step = (np.random.rand(dims) - 0.5) * 0.1
-        line_data[:, index] = line_data[:, index - 1] + step
-    return line_data
 
-
-def update_lines(num, data_lines, lines):
-    for line, data in zip(lines, data_lines):
+def update_lines(num, walks, lines):
+    for line, walk in zip(lines, walks):
         # NOTE: there is no .set_data() for 3 dim data...
-        line.set_data(data[0:2, :num])
-        line.set_3d_properties(data[2, :num])
+        line.set_data(walk[:num, :2].T)
+        line.set_3d_properties(walk[:num, 2])
     return lines
 
 
+# Data: 40 random walks as (num_steps, 3) arrays
+num_steps = 30
+walks = [random_walk(num_steps) for index in range(40)]
+
 # Attaching 3D axis to the figure
 fig = plt.figure()
 ax = fig.add_subplot(projection="3d")
 
-# Fifty lines of random 3-D lines
-data = [gen_rand_line(25, 3) for index in range(50)]
-
-# Creating fifty line objects.
-# NOTE: Can't pass empty arrays into 3d version of plot()
-lines = [ax.plot(dat[0, 0:1], dat[1, 0:1], dat[2, 0:1])[0] for dat in data]
+# Create lines initially without data
+lines = [ax.plot([], [], [])[0] for _ in walks]
 
 # Setting the axes properties
-ax.set_xlim3d([0.0, 1.0])
-ax.set_xlabel('X')
-
-ax.set_ylim3d([0.0, 1.0])
-ax.set_ylabel('Y')
-
-ax.set_zlim3d([0.0, 1.0])
-ax.set_zlabel('Z')
-
-ax.set_title('3D Test')
+ax.set(xlim3d=(0, 1), xlabel='X')
+ax.set(ylim3d=(0, 1), ylabel='Y')
+ax.set(zlim3d=(0, 1), zlabel='Z')
 
 # Creating the Animation object
-line_ani = animation.FuncAnimation(
-    fig, update_lines, 50, fargs=(data, lines), interval=50)
+ani = animation.FuncAnimation(
+    fig, update_lines, num_steps, fargs=(walks, lines), interval=100)
 
 plt.show()