Mining: Which Pits to Work and When to Close Them Down

The following data sets and macro variables contain the input data that are used in this example:

data mine_data;
   input mine $ cost extract_ub quality;
   datalines;
mine1 5 2   1.0
mine2 4 2.5 0.7
mine3 4 1.3 1.5
mine4 5 3   0.5
;

data year_data;
   input year quality_required;
   datalines;
1 0.9
2 0.8
3 1.2
4 0.6
5 1.0
;

%let max_num_worked_per_year = 3;
%let revenue_per_ton = 10;
%let discount_rate = 0.10;