Description

Simple newsboy problem.
Random parameter D has a discrete distribution.

Small Model of Type : SP

Category : GAMS EMP library

Main file : nbsimple.gms

$title Simple newsboy problem, discrete (NBSIMPLE,SEQ=85)

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Simple newsboy problem.
Random parameter D has a discrete distribution.

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Scalar  c       Purchase costs per unit                                 / 30 /
        p       Penalty shortage cost per unit unsatisfied demand       /  5 /
        h       Holding cost per unit leftover                          / 10 /
        v       Revenue per unit sold                                   / 60 /
*       Random parameters
        d       Demand                                                  / 63 /;

Variable Z Profit;
Positive Variables
         X Units bought
         I Inventory
         L Lost sales
         S Units sold;

Equations Row1, Row2, Profit;

* demand = UnitsSold + LostSales
Row1.. d =e= S + L;

* Inventory = UnitsBought = UnitsSold
Row2.. I =e= X - S;

* Profit, to be maximized;
Profit..  Z =e= v*S - c*X - h*I - p*L;

Model nb / all /;

file emp / '%emp.info%' /; put emp '* problem %gams.i%'/;
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randvar d discrete 0.7 45
                   0.2 40
                   0.1 50
stage 2 I L S d
stage 2 Row1 Row2
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putclose emp;

Set scen        Scenarios / s1*s6 /;
Parameter
    s_d(scen)   Demand realization by scenario
    s_x(scen)   Units bought by scenario
    s_s(scen)   Units sold by scenario;

Set dict / scen .scenario.''
           d    .randvar .s_d
           s    .level   .s_s
           x    .level   .s_x /;

solve nb max z use emp scenario dict;
Display s_d, s_x, s_s;