

SteppedStochasticCalc contains the particle number based calculation with fixed timesteps 
where a number of diffusion events and reactions is generated for each reaction, volume and 
volume-volume connection at each timestep.


The DeterministicGridCalc is the opposite extereme - everything isn continuous.

In between there shold be the  MixedStochasicCalc which treats large densities continuously, and 
small ones approximately.

And a SemiExactSteppedStochasticCalc, that is exact for very small number densities where the
changes within a step can be significant - direct or next reaction method.



Performance

Java - 
     Math.random costs about 3 times as much as NRRandom.random
     Math.log costs more than either and should be avoided within the main loop.


C - 
    GCJ - unclear - vanilla use doesn't improve on Math.log. May be a matter 
    of compiler and linker options...

