The method returns string value, which represents prediction expression written in polish postfix notation.
The interpretation of the prediction expression is very simple. For example, let's take a look at sample expression, which was received with window size equal to 5: $0 $1 - $5 / $2 * The above expression in postfix polish notation should be interpreted as a next expression: ( ( x[t - 1] - x[t - 2] ) / const1 ) * x[t - 3]