--- a/nnet_ops.py	Tue Jul 08 01:57:33 2008 -0400
+++ b/nnet_ops.py	Tue Jul 08 01:58:16 2008 -0400
@@ -379,3 +379,11 @@
 def crossentropy_softmax_1hot(x, y_idx, **kwargs):
     b = tensor.zeros_like(x[0,:])
     return crossentropy_softmax_1hot_with_bias(x, b, y_idx, **kwargs)
+
+def binary_crossentropy(output, target):
+    """
+    Compute the crossentropy of binary output wrt binary target.
+    @note: We do not sum, crossentropy is computed by component.
+    @todo: Rewrite as a scalar, and then broadcast to tensor.
+    """
+    return -(target * t.log(output) + (1 - target) * t.log(1 - output))