File:Hopf bifurcation, with limit cycle up to order 3-2..gif

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Summary

Description
English: Hopf bifurcation, with limit cycle up to order 3.

Matplotlib code

from tqdm import tqdm
import numpy as np
import matplotlib.pyplot as plt
from scipy.integrate import solve_ivp
import os

escape_size = 2.0 # If a trajectory is this distance away from 0, we assume it has escaped and stop simulating it.
max_mu = 0.22
mu_resolution = 120
mus = np.linspace(0.001, max_mu, mu_resolution) ** 2
for i, mu in enumerate(tqdm(mus)):
  fig, ax = plt.subplots(figsize=(16,16))

  def system(t, y):
      v, w = y
      dv = mu * v + w - v**2
      dw = -v + mu * w + 2 * v**2
      dv *= (np.abs(v) < 2.0) * (np.abs(w) < 2.0)
      dw *= (np.abs(v) < 2.0) * (np.abs(w) < 2.0)
      return [dv, dw]
  def system_reversed(t, y):
      v, w = y
      dv = mu * v + w - v**2
      dw = -v + mu * w + 2 * v**2
      dv *= (np.abs(v) < 2.0) * (np.abs(w) < 2.0)
      dw *= (np.abs(v) < 2.0) * (np.abs(w) < 2.0)
      return [-dv, -dw]

  x_root = (mu**2+1)/(2+mu)
  y_root = -mu * x_root + x_root ** 2
  vmin, vmax, wmin, wmax = -0.4,0.4,-0.4,0.4

  # Hopf bifurcation circle
  if mu > 0:
      thetas = np.linspace(0, 2*np.pi, 1000)
      xs = np.sqrt(2*mu) * np.cos(thetas)
      ys = -np.sqrt(2*mu) * np.sin(thetas)
      ax.plot(xs, ys, color='r', linewidth=1, label="$\mu^{1/2}$ order")  
      xs += mu * (2-2/3 * np.sin(2*thetas)-2/3 * np.cos(2*thetas))
      ys += mu * (1+4/3*np.sin(2*thetas) - 1/3*np.cos(2*thetas))
      ax.plot(xs, ys, color='b', linewidth=1, label="$\mu$ order")  
      xs += mu**1.5 / np.sqrt(72) * (5 * np.sin(3*thetas) - np.cos(3*thetas))
      ys += mu**1.5 / np.sqrt(72) * (36 * np.sin(thetas) + 28 * np.cos(thetas) - 5 * np.sin(3*thetas) + 7 * np.cos(3*thetas))
      ax.plot(xs, ys, color='k', linewidth=1, label="$\mu^{3/2}$ order")  
      radius = xs[0]

  t_span = np.array([0, 14])
  trajectory_resolution = 10

  epsilon = 0.01

  initial_conditions = []
  initial_conditions += [(x, 0)  for x in np.linspace(vmin, vmax, trajectory_resolution)]
  initial_conditions_2 = []
  if mu > 0:
    initial_conditions_2 = [(radius *(1 + dx), 0) for dx in np.linspace(-0.08, 0.08, 5)]
  sols = {}
  sols_2 = {}
  for ic in initial_conditions:
      sols[ic] = solve_ivp(system, [0,50], ic, dense_output=True, max_step=0.05)
  for ic in initial_conditions_2:
      sols_2[ic] = solve_ivp(system, [0, min(0.1 * t_span[1]/mu, 200)], ic, dense_output=True, max_step=0.05)

  vs = np.linspace(vmin, vmax, 200)
  v_axis = np.linspace(vmin, vmax, 20)
  w_axis = np.linspace(wmin, wmax, 20)


  v_values, w_values = np.meshgrid(v_axis, w_axis)

  dv, dw = system(0, [v_values, w_values])

  # integral curves
  # ax.scatter([x for x, y in initial_conditions_2], [y for x, y in initial_conditions_2])
  for ic in initial_conditions:
    sol = sols[ic]
    ax.plot(sol.y[0], sol.y[1],alpha=0.2, linewidth=0.5, color='k')
  for ic in initial_conditions_2:
    sol = sols_2[ic]
    ax.plot(sol.y[0], sol.y[1],alpha=0.3, linewidth=0.5, color='g')

  # vector fields
  arrow_lengths = np.sqrt(dv**2 + dw**2)
  alpha_values = 1 - (arrow_lengths / np.max(arrow_lengths))**0.4
  ax.quiver(v_values, w_values, dv, dw, color='blue', linewidth=0.5, scale=25, alpha=alpha_values)

  ax.set_title(f'Hopf Bifurcation Model
$\mu={mu:.4f}}})

  # ax.legend()
  ax.set_xlim(vmin, vmax)
  ax.set_ylim(wmin, wmax)
  ax.legend(loc='lower left')
  # ax.set_xticks([])
  # ax.set_yticks([])
  dir_path = f"./hopf_3"
  if not os.path.exists(dir_path):
    os.makedirs(dir_path)

  fig.savefig(f"{dir_path}/{i}.png")
  # plt.show()
  plt.close()

import imageio.v3 as iio
from natsort import natsorted
import moviepy.editor as mp

for dir_path in ["./hopf_3"]:
    file_names = natsorted((fn for fn in os.listdir(dir_path) if fn.endswith('.png')))

    # Create a list of image files and set the frame rate
    images = []
    fps = 12

    # Iterate over the file names and append the images to the list
    for file_name in file_names:
        file_path = os.path.join(dir_path, file_name)
        images.append(iio.imread(file_path))

    filename = dir_path[2:]
    iio.imwrite(f"{filename}.gif", images, duration=1000/fps, rewind=True)
    clip = mp.ImageSequenceClip(images, fps=fps)
    clip.write_videofile(f"{filename}.mp4")

Date
Source Own work
Author Cosmia Nebula

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current08:00, 27 April 2023Thumbnail for version as of 08:00, 27 April 20231,600 × 1,600 (12.09 MB)wikimediacommons>Cosmia NebulaUploaded while editing "Hopf bifurcation" on en.wikipedia.org

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