[artin haroutunian]

Hi everybody,
I have a question about how does fluent deal with terms of a user defined scalar equation. I want to know if it is necessary to define all 4 terms (unsteady,diffusion,convection and source) of a UDS equation even if some of them are equal to zero!? I mean for example if the UDS has only diffusion and source terms, is it necessary to set convetive and unsteady sources equal to zero or fluent does this autumatically. Or is it ok to only define a diffusion coefficient equal to "1" to specify the laplace equation!?
I'll be so thankful if someone helps me.
Thanks a lot