Component activities in liquid mixture, using NRTL

This is a simple code that calculates the activities of the different components present in a liquid mixture, using the Non-Random Two Liquid model, extended to multiple components. The code has not been verified in any way, but may still be useful for others to use. Please feel free to use, modify and distribute the files. If you think the files are useful a positive notification would be appreciated. If the code contains errors, please let me know.