Q:

Matlab neural network testing

I have created a neural network and the performance is good.  By using nprtool, we are allow to test the network with an input data and target data.  Here is my question, what is the purpose of testing a neural network with target data provided?  Isn't it testing should not hav e target data so that we can know how well can the trained neural network perform without target data is given?  Hope someone will respond to this, thanks =)  

A:

I'm not familiar with nprtool, but I suspect it would give the input data to your neural network, and then compare your NN's output data with the target data (and compute some kind of success rate based on that). 
So your NN will never see the target data, it's just used to measure the performance. 
It's like the "teacher's edition" of the exercise books in school.  The student (i.e. the NN) doesn't have the solutions, but her/his answers will be compared against them by the teacher (i.e. nprtool). ( Okay, the teacher probably/hopefully knows the subject, but you get the idea.)