#63 Error function for financial forecasting

[Paolo Marrone]

At http://citeseer.ist.psu.edu/527631.html , is a paper
by Yao, Tan that treats about the error function for
financial forecasting and tells that a two other
functions should be combined with the RMSE or NMSE,
they apply two factors, one that cares for profit and
the other one that cares for timing of profit. It
should be very simple to implement in Joone. (signaled
by ghcmartins2)