プログラミング問題集解答例（問３５）

import numpy as np
def rotation(x, t, deg = False):
    if deg == True:
        t = np.deg2rad(t)
    a = np.array([[np.cos(t), -np.sin(t)],
                  [np.sin(t),  np.cos(t)]])
    ax = np.dot(a, x)        
    return ax

n = 5
angle = 360 / n
P = []
x0 = [0, 1]
P.append(x0)
for i in range(n):
    x = rotation(P[i], angle * 2, deg=True)
    P.append(x)

%matplotlib inline
import matplotlib.pyplot as plt

plt.figure(figsize=(6,6))
plt.plot(np.array(P)[:, 0], np.array(P)[:, 1])
plt.show()

plt.figure(figsize=(6,6))
for n in [19]:
    angle = 360 / n
    P = []
    x0 = [0, 1]
    P.append(x0)
    for i in range(n):
        x = rotation(P[i], angle * int(n/2), deg=True)
        P.append(x)
    plt.plot(np.array(P)[:, 0], np.array(P)[:, 1])
plt.show()

plt.figure(figsize=(6,6))
n = 19
for m in [2, 3, 4, 5, 6, 7, 8, 9, 10]:
    angle = 360 / n
    P = []
    x0 = [0, 1]
    P.append(x0)
    for i in range(n):
        x = rotation(P[i], angle * m, deg=True)
        P.append(x)
    plt.plot(np.array(P)[:, 0], np.array(P)[:, 1])
plt.show()