Hi Alireza,
You can make use of the Regression Learner App available in MATLAB, as it helps to choose, various algorithms to train and validate regression models. After training multiple models, it also compares the validation errors side-by-side, and then chooses the best model.
If you want to implement it using nntool method, instead of nntool method, I recommend you to use nnstart method which provides graphical interfaces that allow you to design and deploy fitting, pattern recognition, clustering, and time-series neural networks.
Hope this Helps!
