Domain Coloring in Python using Matplotlib (algorithm-archivists#788)

* Added domain coloring in Python

* Some cleanup

Author: 0xJonas

contents/domain_coloring/code/python/domain_coloring.py

@@ -0,0 +1,83 @@
+
+import numpy as np
+import matplotlib.pyplot as plt
+import matplotlib.colors
+from matplotlib.cm import ScalarMappable
+
+
+def f(z):
+    return z**2
+
+
+def magnitude_shading(f_val):
+    f_val_abs = np.abs(f_val)
+    return 0.5 + 0.5 * (f_val_abs - np.floor(f_val_abs))
+
+
+def gridlines(f_val, threshold):
+    return (np.abs(np.sin(np.pi * np.real(f_val))) ** threshold
+            * np.abs(np.sin(np.pi * np.imag(f_val))) ** threshold)
+
+
+def color(f_val, threshold):
+    hue = (np.pi - np.angle(f_val)) / (2.0 * np.pi)
+    saturation = magnitude_shading(f_val)
+    value = gridlines(f_val, threshold)
+
+    # Currently we have a tuple of 2D-arrays (hue, saturation, value).
+    # This makes it a 2D-array of tuples, which the conversion function requires.
+    hsv = np.moveaxis((hue, saturation, value), 0, -1)
+    return matplotlib.colors.hsv_to_rgb(hsv)
+
+
+if __name__ == "__main__":
+    # Create a new figure containing a single plot
+    fig, axes = plt.subplots(1, 1)
+
+    # Set the title for the plot
+    axes.set_title("$f(x)=z^2$")
+
+    # Create color bar
+    cbar = fig.colorbar(
+        ScalarMappable(matplotlib.colors.Normalize(0.0, 2.0 * np.pi), "hsv"),
+        ax=axes,
+        label="Phase Angle")
+
+    # Set x and y labels
+    axes.set_xlabel("$Re(z)$")
+    axes.set_ylabel("$Im(z)$")
+    
+    # Set color bar tick locations and labels
+    cbar.set_ticks([0.0, np.pi, 2.0 * np.pi])
+    cbar.set_ticklabels(["$0.0$", "$\pi$", "$2\pi$"])
+
+    # Hide x and y ticks
+    for tick in axes.get_xticklines():
+        tick.set_visible(False)
+
+    for tick in axes.get_yticklines():
+        tick.set_visible(False)
+
+    # Create a 500x500 input grid
+    coords = np.linspace(-2.0, 2.0, 500)
+    z_real, z_imag = np.meshgrid(coords, coords)
+    z = z_real + 1j * z_imag
+
+    # Calculate function values
+    f_val = f(z)
+
+    # Map function values to colors
+    colors = color(f_val, 0.1)
+
+    # Plot the colors
+    #   extent=(-2.0, 2.0, -2.0, 2.0) sets the x and y ranges
+    #   origin="lower" places index (0,0) of the color array in the lower-left corner
+    #   aspect="equal" ensures that the plot is square
+    axes.imshow(
+        colors,
+        extent=(-2.0, 2.0, -2.0, 2.0),
+        origin="lower",
+        aspect="equal")
+
+    # Save output
+    fig.savefig("domain.png")

contents/domain_coloring/domain_coloring.md

@@ -174,6 +174,8 @@ Here is the full script to generate a domain colored output of $$f(z)=z^2$$.
 {% method %}
 {% sample lang="gnuplot" %}
 [import, lang:"gnuplot"](code/gnuplot/domain_coloring.gp)
+{% sample lang="python & matplotlib" %}
+[import, lang:"python"](code/python/domain_coloring.py)
 {% endmethod %}
 
 ### Bibliography