what is the equation for bose einstien condensate?
It is a state of matter. There is no "equation" for it.
The particles involved that make up a Bose-Einstein condensate (BEC) must have spin that is either zero or an integer (not a half-integer), in units of h/(2 pi). "h" is Planck's constant.
There is a critical temperture that a substance must be below to be in a BEC state. There is an equation for that at
http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate