Length : around 15 minutes
First part :
Based on the following programme excerpt :
*---------- DECLARATIONS ----------* sets C crops /wheat,maize/ ; *---------- DATA ----------* scalar LAND_A land availability in hectares /50/ LABOUR_A labour availability in hours /2000/ ; parameter LN(C) labour needs per hectare and per crop (hours) /wheat 25 maize 50/ YLD (C) yield per crop in tonnes per hectare / wheat 5 maize 10/ PC (C) selling price per crop in euros / wheat 150 maize 150/ COST (C) cost per crop in euros per ha / wheat 300 maize 500/ ; parameter GM(C) gross margin per crop in euros ; GM(C) = YLD(C)*PC(C)-COST(C); *---------- MODEL ----------* variables Z total fram income (euros) ; positive variables X area per crop (hectares) ; equations OBJECTIVE objective function LAND land equation LABOUR labour equation ; OBJECTIVE.. sum(c, GM(c)*X(c)) =E= Z ; LAND.. sum(c, X(c)) =l= LAND_A ; LABOUR.. sum(c, LN(c)*X(c)) =L= LABOUR_A ; model example first example /all/; *---------- SOLUTION ----------* solve example using LP maximizing Z; display X.m ; display C;
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Second part :
Download the primal1.zip file and unzip it to your GAMS project folder (if you have not already done it), then open it in GAMS. Add the necessary lines to the model in order to display :
- The marginal value of the labour equation
- The optimum value of areas
- The minimum value of the soil equation
- The gross margin parameter