compare backend alg example

examples/cpp/alg_comparison.py

+from __future__ import print_function
+from topologylayer.nn import LevelSetLayer1D
+import matplotlib.pyplot as plt
+
+import torch
+import time
+import numpy as np
+
+
+def sum_finite(d):
+    diff = d[:,0] - d[:,1]
+    inds = diff < np.inf
+    return torch.sum(diff[inds])
+
+# apparently there is some overhead the first time backward is called.
+# we'll just get it over with now.
+n = 20
+y = torch.rand(n, dtype=torch.float).requires_grad_(True)
+layer1 = LevelSetLayer1D(n, False)
+dgm, issublevel = layer1(y)
+p = sum_finite(dgm[0])
+p.backward()
+
+algs = ['hom', 'cohom']
+
+tcs = {}
+tfs = {}
+tbs = {}
+for alg in algs:
+    tcs[alg] = []
+    tfs[alg] = []
+    tbs[alg] = []
+
+
+ns = [100, 200, 400, 1000, 2000, 4000, 8000, 16000]
+
+for alg in algs:
+    for n in ns:
+        y = torch.rand(n, dtype=torch.float).requires_grad_(True)
+
+        t0 = time.time()
+        layer = LevelSetLayer1D(n, False, alg=alg)
+        ta = time.time() - t0
+        tcs[alg].append(ta)
+
+        t0 = time.time()
+        dgm, issublevel = layer(y)
+        ta = time.time() - t0
+        tfs[alg].append(ta)
+
+        p = sum_finite(dgm[0])
+        t0 = time.time()
+        p.backward()
+        ta = time.time() - t0
+        tbs[alg].append(ta)
+
+for alg in algs:
+    plt.loglog(ns, tfs[alg], label=alg)
+plt.legend()
+plt.xlabel("n")
+plt.ylabel("forward time")
+plt.savefig("alg_time_forward.png")