 Hi everybody,    
  consider please an optimization problem:  
   
  minimize   sum S1+S2
   
  Subject to :  y - x =< A + S1
                     x - y =< A + S2
   
  and we want to add two more constraints:
   
                   y - x =< B - S3
                   x - y =< B - S4
   
  where A is a small constant value and B is a large constant value, S1 and S2 are surplus and S3 and S4 are slack variables.
   
  S3 and S4 have to be maximized in objective function. As objective function, is this correct?  :
   
  minimize sum S1+ S2 - S3 -S4
   
  where actually we want to minimize S1 and S2; and maximize S3 and S4.
   
  If it is not correct, what to do ?
   
  Thank you for any guide.
   
  Tobias

 
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