About feature in analysis.c

[MichelleYang2017]

Hello,there is a problem about feature extraction in analysis.c file. In feature extraction process, there are many constant values(ie.spec_variability - 0.78f; info->tonality - 0.154723f;).Why are these constants and why use these features? These features are more effective than mfcc etc. but I don’t really understand the reasons for choosing these features. Is there some information for reference? Thanks!