Added example for multi selector

examples/selector.py

@@ -1,5 +1,6 @@
 from functools import partial
 
+import numpy as np
 import matplotlib.pyplot as plt
 from matplotlib import cm
 
@@ -41,3 +42,36 @@ plt.xlabel(r"$t$ / ps")
 plt.ylabel(r"S_q(t)")
 plt.savefig(f"{data_dir}/selector.png", dpi=300, bbox_inches="tight")
 plt.show()
+
+
+def multi_radial_selector(atoms, bins):
+    indices = []
+    for i in range(len(bins) - 1):
+        index = md.coordinates.selector_radial_cylindrical(
+            atoms, r_min=bins[i], r_max=bins[i + 1]
+        )
+        indices.append(index)
+    return indices
+
+
+bins = np.arange(0.0, 1.6, 0.1)
+r = (bins[:-1] + bins[1:]) / 2
+
+time, results = md.correlation.shifted_correlation(
+    partial(md.correlation.isf, q=22.7),
+    oxygen_water,
+    selector=partial(multi_radial_selector, bins=bins),
+    segments=100,
+    skip=0.1,
+)
+
+c = [cm.plasma(i) for i in np.linspace(0, 1, len(r))]
+plt.figure()
+for i, result in enumerate(results):
+    plt.plot(time, result, "-", c=c[i], label=round(r[i], 2))
+plt.legend(title=r"$r$ / nm", ncols=2)
+plt.xscale("log")
+plt.xlabel(r"$t$ / ps")
+plt.ylabel(r"S_q(t)")
+plt.savefig(f"{data_dir}/multi_selector.png", dpi=300, bbox_inches="tight")
+plt.show()