Update otter.py (#359)

* Update otter.py

Author: marouenbg

netZooPy/otter/otter.py

@@ -48,7 +48,9 @@ def otter(W, P, C, lam=0.035, gamma=0.335, Iter=60, eta=0.00001, bexp=1):
 
     C = C  / np.trace(C)
     W = W / np.sqrt(np.trace(W @ W.T))
-    P = P / np.trace(P)
+    diagP =  np.trace(P)
+    if diagP > 0:
+        P = P / np.trace(P)
 
     P = P * (-(1 - lam)) + gamma * np.identity(t)
     C = C * (-lam)
@@ -138,4 +140,4 @@ def otter_gpu(W, P, C, lam=0.035, gamma=0.335, Iter=60, eta=0.00001, bexp=1):
 
     W1 = cp.asnumpy(W)
     del W,C,P   
-    return W1
+    return W1