In certain cases program can generate NaN (Not a Number) values as an output. It is caused by improper inputs in certain calculations, such as input value 0 in the cumulative computations. If you find a bug, please don't hesitate to contact us at email address Amaury.Lataillade@enstimac.fr and describe your experiences with the problem. We don't feel the program is bug free and any hints are appreciated.