#!/usr/bin/env python3
 
import matplotlib.pyplot as plt
from functools import reduce
 
m, k, dt, x_table, v_table = 1, 10, 0.01, {}, {}
 
def v_(n_max):
    def foo(v_n, n):
        try: v_n -= (k/m) * x_table[n-1] * dt
        except KeyError:
            x_table[n-1] = x_(n-1)
            v_n -= (k/m) * x_table[n-1] * dt
        finally: v_table[n] = v_n
        return v_table[n]
    return reduce(foo, range(1, n_max+1), 0)
 
def x_(n_max):
    def foo(x_n, n):
        try: x_n += v_table[n] * dt
        except KeyError:
            v_table[n] = v_(n)
            x_n += v_table[n] * dt
        finally: x_table[n] = x_n
        return x_table[n]
    return reduce(foo, range(1, n_max+1), 1)
 
if __name__ == '__main__':
    x_(500) # 出力せずにここで一回計算させただけでハッシュに値が登録される
    t = [i * dt for i in x_table.keys()]
    x = [i for i in x_table.values()]
    plt.plot(t, x)
    plt.savefig('t-x.png')
    plt.show()
 

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