python爬虫python-fractals.rar

"""Author Alexandre De Zotti Draws Julia sets of quadratic polynomials and exponential maps. More specifically, this iterates the function a fixed number of times then plots whether the absolute value of the last iterate is greater than a fixed threshold (named "escape radius"). For the exponential map this is not really an escape radius but rather a convenient way to approximate the Julia set with bounded orbits. The examples presented here are: - The Cauliflower Julia set, see e.g. https://en.wikipedia.org/wiki/File:Julia_z2%2B0,25.png - Other examples from https://en.wikipedia.org/wiki/Julia_set - An exponential map Julia set, ambiantly homeomorphic to the examples in https://www.math.univ-toulouse.fr/~cheritat/GalII/galery.html and https://ddd.uab.cat/pub/pubmat/02141493v43n1/02141493v43n1p27.pdf Remark: Some overflow runtime warnings are suppressed. This is because of the way the iteration loop is implemented, using numpy's efficient computations. Overflows and infinites are replaced after each step by a large number. """ import warnings from collections.abc import Callable from typing import Any import matplotlib.pyplot as plt import numpy as np c_cauliflower = 0.25 + 0.0j c_polynomial_1 = -0.4 + 0.6j c_polynomial_2 = -0.1 + 0.651j c_exponential = -2.0 nb_iterations = 56 window_size = 2.0 nb_pixels = 666 def eval_exponential(c_parameter: complex, z_values: np.ndarray) -> np.ndarray: """ Evaluate $e^z + c$. >>> eval_exponential(0, 0) 1.0 >>> abs(eval_exponential(1, np.pi*1.j)) < 1e-15 True >>> abs(eval_exponential(1.j, 0)-1-1.j) < 1e-15 True """ return np.exp(z_values) + c_parameter def eval_quadratic_polynomial(c_parameter: complex, z_values: np.ndarray) -> np.ndarray: """ >>> eval_quadratic_polynomial(0, 2) 4 >>> eval_quadratic_polynomial(-1, 1) 0 >>> round(eval_quadratic_polynomial(1.j, 0).imag) 1 >>> round(eval_quadratic_polynomial(1.j, 0).real) 0 """ return z_values * z_values + c_parameter def prepare_grid(window_size: float, nb_pixels: int) -> np.ndarray: """ Create a grid of complex values of size nb_pixels*nb_pixels with real and imaginary parts ranging from -window_size to window_size (inclusive). Returns a numpy array. >>> prepare_grid(1,3) array([[-1.-1.j, -1.+0.j, -1.+1.j], [ 0.-1.j, 0.+0.j, 0.+1.j], [ 1.-1.j, 1.+0.j, 1.+1.j]]) """ x = np.linspace(-window_size, window_size, nb_pixels) x = x.reshape((nb_pixels, 1)) y = np.linspace(-window_size, window_size, nb_pixels) y = y.reshape((1, nb_pixels)) return x + 1.0j * y def iterate_function( eval_function: Callable[[Any, np.ndarray], np.ndarray], function_params: Any, nb_iterations: int, z_0: np.ndarray, infinity: float | None = None, ) -> np.ndarray: """ Iterate the function "eval_function" exactly nb_iterations times. The first argument of the function is a parameter which is contained in function_params. The variable z_0 is an array that contains the initial values to iterate from. This function returns the final iterates. >>> iterate_function(eval_quadratic_polynomial, 0, 3, np.array([0,1,2])).shape (3,) >>> np.round(iterate_function(eval_quadratic_polynomial, ... 0, ... 3, ... np.array([0,1,2]))[0]) 0j >>> np.round(iterate_function(eval_quadratic_polynomial, ... 0, ... 3, ... np.array([0,1,2]))[1]) (1+0j) >>> np.round(iterate_function(eval_quadratic_polynomial, ... 0, ... 3, ... np.array([0,1,2]))[2]) (256+0j) """ z_n = z_0.astype("complex64") for _ in range(nb_iterations): z_n = eval_function(function_params, z_n) if infinity is not None: np.nan_to_num(z_n, copy=False, nan=infinity) z_n[abs(z_n) == np.inf] = infinity return z_n def show_results( function_label: str, function_params: Any, escape_radius: float, z_final: np.ndarray, ) -> None: """ Plots of whether the absolute value of z_final is greater than the value of escape_radius. Adds the function_label and function_params to the title. >>> show_results('80', 0, 1, np.array([[0,1,.5],[.4,2,1.1],[.2,1,1.3]])) """ abs_z_final = (abs(z_final)).transpose() abs_z_final[:, :] = abs_z_final[::-1, :] plt.matshow(abs_z_final < escape_radius) plt.title(f"Julia set of ${function_label}$, $c={function_params}$") plt.show() def ignore_overflow_warnings() -> None: """ Ignore some overflow and invalid value warnings. >>> ignore_overflow_warnings() """ warnings.filterwarnings( "ignore", category=RuntimeWarning, message="overflow encountered in multiply" ) warnings.filterwarnings( "ignore", category=RuntimeWarning, message="invalid value encountered in multiply", ) warnings.filterwarnings( "ignore", category=RuntimeWarning, message="overflow encountered in absolute" ) warnings.filterwarnings( "ignore", category=RuntimeWarning, message="overflow encountered in exp" ) if __name__ == "__main__": z_0 = prepare_grid(window_size, nb_pixels) ignore_overflow_warnings() # See file header for explanations nb_iterations = 24 escape_radius = 2 * abs(c_cauliflower) + 1 z_final = iterate_function( eval_quadratic_polynomial, c_cauliflower, nb_iterations, z_0, infinity=1.1 * escape_radius, ) show_results("z^2+c", c_cauliflower, escape_radius, z_final) nb_iterations = 64 escape_radius = 2 * abs(c_polynomial_1) + 1 z_final = iterate_function( eval_quadratic_polynomial, c_polynomial_1, nb_iterations, z_0, infinity=1.1 * escape_radius, ) show_results("z^2+c", c_polynomial_1, escape_radius, z_final) nb_iterations = 161 escape_radius = 2 * abs(c_polynomial_2) + 1 z_final = iterate_function( eval_quadratic_polynomial, c_polynomial_2, nb_iterations, z_0, infinity=1.1 * escape_radius, ) show_results("z^2+c", c_polynomial_2, escape_radius, z_final) nb_iterations = 12 escape_radius = 10000.0 z_final = iterate_function( eval_exponential, c_exponential, nb_iterations, z_0 + 2, infinity=1.0e10, ) show_results("e^z+c", c_exponential, escape_radius, z_final)