What do you mean by change [u]just number of particles, ideal gas(mass of particles), and volume.[/u]
Do you mean change all of the above 3 patrameter at the same time and without changing other parameters?
If you can freely change V and N, there is no way to keep P and T constant (unless V/N is keep as constant,too!)
When you use mouse to change parameters, you can adjust one parameter at a time.
Let me know exactly what you want to do. Please give me an example (in detail) and I will try to find way to help you! O.K.?
Please write it in detail!