With recent versions of numpy, the original expression results in:

TypeError: Cannot cast ufunc add output from dtype('float64') to dtype('int64')
with casting rule 'same_kind'

This patch solves the issue by not trying to add in place.

diff -Naur networkx-networkx-1.10.orig/networkx/linalg/algebraicconnectivity.py networkx-networkx-1.10/networkx/linalg/algebraicconnectivity.py
--- networkx-networkx-1.10.orig/networkx/linalg/algebraicconnectivity.py	2015-10-30 15:41:35.000000000 -0600
+++ networkx-networkx-1.10/networkx/linalg/algebraicconnectivity.py	2015-12-01 09:49:51.568953316 -0700
@@ -244,8 +244,7 @@
             W -= (W.T * X * X.T).T
             project(W)
             # Compute the diagonal of P * L * P as a Jacobi preconditioner.
-            D = L.diagonal()
-            D += 2. * (asarray(X) * asarray(W)).sum(axis=1)
+            D = L.diagonal() + 2. * (asarray(X) * asarray(W)).sum(axis=1)
             D += (asarray(X) * asarray(X * (W.T * X))).sum(axis=1)
             D[D < tol * Lnorm] = 1.
             D = 1. / D