Based on each of the N feature sets, an NN algorithm predictor was constructed and tested with the jackknife cross-validation test. With all the N overall accurate rates calculated, we could draw an IFS curve with the index i to be the x-axis and the corresponding overall accurate rate to be the y-axis. Thus, S opt~f f 1 , f 2 , :::, f n g is regarded as the optimal feature set if the curve reach its peak where the value of its x-axis is nƒN.