Additionally to concentration profile dependent criteria, we obey two geometrical conditions for the grid spacing. First, the grid spacing must not exceed given maximum and minimum values (3.6-21), and second, the grid spacing must not change too abrupt (3.6-22). The latter supports the reduction of interpolation and discretization errors.
For the actual decision if a grid line may be deleted or need to be inserted
we take the maximum of the respective dose conservation and gradient
resolution criteria. We start deleting grid lines with the lowest `delete'
criterion and insert a corresponding number of grid lines starting with the
line with highest `insert' criterion. We terminate deleting/inserting
grid lines when the ratio of remaining maximum `insert' criterion to
remaining minimum `delete' criterion falls short of a given grid uniformity
limit (
), or when more than about 15% new grid lines
have been inserted.
