Create plot_contour_for_fixed_value.py

language_learning/2023.02.18_plot_contour_for_fixed_value/plot_contour_for_fixed_value.py

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+"""
+This code is supported by the website: https://www.guanjihuan.com
+The newest version of this code is on the web page: https://www.guanjihuan.com/archives/29155
+"""
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+def get_data(x_array, y_array):
+    z_matrix = np.zeros((y_array.shape[0], x_array.shape[0]))
+    j0 = -1
+    for x in x_array:
+        j0 += 1
+        i0 = -1
+        for y in y_array:
+            i0 += 1
+            z_matrix[i0, j0] = x**2+y**2
+    return z_matrix
+
+x_array = np.linspace(-1, 1, 1000)
+y_array = x_array
+z_matrix = get_data(x_array, y_array)  # 举例的数据
+
+fix_value = 0.5  # 画这个值附近的等高线
+precision = 0.01 # 选取该值附近的范围
+
+# 方法一
+x_array_new = []
+y_array_new = []
+for i0 in range(y_array.shape[0]):
+    for j0 in range(x_array.shape[0]):
+        if abs(z_matrix[i0, j0]-fix_value)<precision:
+            x_array_new.append(x_array[j0])
+            y_array_new.append(y_array[i0])
+fig, ax = plt.subplots()
+plt.plot(x_array_new, y_array_new, 'o')
+ax.set_xlim(min(x_array), max(x_array))
+ax.set_ylim(min(y_array), max(y_array))
+plt.show()
+
+# 方法二
+for i0 in range(y_array.shape[0]):
+    for j0 in range(x_array.shape[0]):
+        if abs(z_matrix[i0, j0]-fix_value)>precision:
+            z_matrix[i0, j0] = None
+fig, ax = plt.subplots()
+ax.contourf(x_array,y_array,z_matrix) 
+plt.show()