The backprop trick

• To find the error value for a given node h in a hidden layer, ...

• Simply take the weighted sum of the errors of all nodes connected from node h

• i.e., of all nodes that have an incoming connection from node h:

?1

?2

?3

?n

w1

w2

w3

wn

?h = w1?1 + w2?2 + w3?3 + ... + wn?n

Node h

This is backpropgation of errors

To-nodes of h