Negative output neural networks

I trained my neural network, but it generates negative values even though the target values are positive. I wonder why ?

Answer 1

[JESUS DAVID ARIZA ROYETH]

the output of the neural network depends on the transfer function of the output layer, if the results are negative you probably have a transfer function like "tansig" or "purelin", I recommend that if you don't want negative values you should change the transfer function, if the answer is in the range from 0 to 1 you can change it to "logsig" or whatever function you desire :

net.Layers{end}.transferFcn='logsig';