clase del 16

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

n = 2
lenght = 100
dt = 0.01
epsilon = 2250  # energía mínima
sigma = 26  # distancia a la cuál es 0


def u(r):
    return 4*epsilon*(pow(sigma/r, 12) - pow(sigma/r, 6))


def f(r):
    return 4*epsilon*(12*sigma**12/r**13 - 6*sigma**6/r**7)


def update(num, pos, pos1, pt):
    aceleraciones = np.zeros((n, 2))
    for i in range(n):
        acc = 0.0
        for j in range(n):
            if i != j:
                d = np.linalg.norm(pos1[i] - pos1[j])
                acc += f(d) * (pos1[i] - pos1[j])/d
                pass
            pass
        aceleraciones[i] = acc
        pass
    pos1c = np.copy(pos1)
    for i in range(n):
        pos1[i] = 2*pos1[i] - pos[i] + aceleraciones[i]*dt**2
        for j in range(2):
            if pos1[i][j] < 0 or pos1[i][j] > lenght:  # si colide con los bordes
                pos1[i][j] = pos1c[i][j]  # no avanza
        pass
    for i in range(n):
        pos[i] = pos1c[i]
        pass
    pt.set_data(pos1[:, 0], pos[:, 1])
    return pt


fig1 = plt.figure()

pos = np.array([[30, 50], [70, 50]], dtype="float64")
vel = np.array([[0, 40], [0, -40]], dtype="float64")

# primer paso
acc = 0.0
for i in range(n):
    for j in range(n):
        if i != j:
            d = np.linalg.norm(pos[i] - pos[j])
            acc += f(d) * (pos[i] - pos[j])/d
pos1 = pos + vel*dt + acc*dt**2/2

pts, = plt.plot([], [], "bo", markersize=10)
plt.xlim(0, lenght)
plt.ylim(0, lenght)

booru = anim.FuncAnimation(fig1, update, fargs=(pos, pos1, pts), interval=50)

plt.show()