1. Your code should yield an error because you have not defined y.
here are two ways to define output y, error e and normalized mean square error NMSE (= 1-Rsquare)
1. [ net tr ] = train(net,x,t);
y = net(x);
e = t-y;
2. [ net tr y e ] = train(net,x,t); % My favorite
then, in general,
NMSE = mse(e)/mean(var(t',1))
or for 1-dimensional outputs
NMSE = mse(e)/var(t,1)
Hope this helps.
Greg
