The number of photos to take in a single burst.

It is an iterative process that helps to produce more realistic models.

However, in the presence of rounding errors this statement does not hold moreover, in practice N can be very large, and the iterative process reaches sufficient accuracy already far earlier.

Computer programs are made to solve the discretized equations using direct methods (which are single step methods resulting in the solution) or iterative methods (which start with a trial solution and arrive at the actual solution by successive refinement).