How can I implement my own custom performance function

Hi All,

I am using nn toolbox functions to create a neural network for classification purpose (2 output neuron). Instead of using standard performance function to be optimized, I want to use my own. Such that my performance function will be:

( fp/(fp+tn) )  + ( fn/(fn+tp) );

where

• tp: true positive
• fn: false negative
• and so on

of course output y of the network must be converted to 0 or 1. maybe like this:

yPred = ( y(:,1) > y(:,2) );

how can I do this with using newpr or newff?

any help appreciated Thanks