public static void SetSigmoid(ref nonlin fun, ref nonlinPrime funprime)
 {
     fun      = Sigmoid;
     funprime = SigmoidPrime;
 }
 public static void SetTansig(ref nonlin fun, ref nonlinPrime funprime)
 {
     fun      = Tansigmoid;
     funprime = Tansigmoid;
 }