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Calcite | Level 5 84
Calcite | Level 5

Hi, I am trying to write a code for a transshipment procurement model from 4 plants (Ps) via 3 transshipment nodes (Ts) to 4 destination distribution centers (DCs). 

The conditon is that each node in the inflow (from Ps to Ts) and outflow (from Ts to Ds) variables need to be a multiple of 3. 


I have tried to do that via introducing the "lot" variable, however it doesn't work correctly when I use lot =3, but it does give a correct answer when lot size = 1.


Can someone kindly, help point out the mistake I am making. Thank you.


My Current Code -


proc optmodel;							
set Ps ={'P1', 'P2', 'P3', 'P4'};							
set Ds ={'D1', 'D2', 'D3', 'D4'};							
set Ts ={'T1', 'T2', 'T3'};							
number InCost{Ps, Ts} = [							
39	29	43					
40	35	43					
48	44	31					
37	39	30];					
number OutCost{Ts, Ds} = [							
34	17	36	25				
30	47	16	15				
29	22	21	23];				
number Supply{Ps} = [37	34	20	28];				
number Demand{Ds} = [18	15	21	3];				
number TransshipmentCapacity {Ts} = [37	37	43];					
number TransshipmentFixedCost{Ts} = [700	700	900];					
number ProductionFixedCost{Ps} = [420	120	240	580];				
var inflow {Ps, Ts} integer>=0;							
var outflow{Ts, Ds} integer>=0;							
number lot = 1;							
var y{Ts} binary;							
var a{Ps} binary;							
number M=1000000;							
number N=1000000;							
minimize Z = sum{i in Ps}sum{j in Ts}(inflow[i,j]*lot)*InCost[i,j]+sum{j in Ts}y[j]*TransshipmentFixedCost[j]							
+sum{i in Ps}a[i]*ProductionFixedCost[i]+sum{j in Ts}sum{k in Ds}(outflow[j,k]*lot)*OutCost[j,k];							
con SupplyConst {i in Ps}:sum{j in Ts}(inflow[i,j]*lot)  <= Supply[i];							
con DemandConst {k in Ds}:sum{j in Ts}(outflow[j,k]*lot) >= Demand[k];							
con NoStockConst{j in Ts}:sum{i in Ps}(inflow[i,j]*lot) = sum{k in Ds}(outflow[j,k]*lot);							
con TsCapConst  {j in Ts}:sum{i in Ps}(inflow[i,j]*lot) <= TransshipmentCapacity[j];							
con linkingy {j in Ts}:sum{i in Ps}(inflow[i,j]*lot)<=M*y[j];							
con linkinga {i in Ps}:sum{j in Ts}(inflow[i,j]*lot)<=N*a[i];							
print inflow;							
print outflow;							
print y;							
print a;							
print Z;							
print {j in Ts} (sum{i in Ps}inflow[i,j]);							
print {j in Ts} (sum{k in Ds}outflow[j,k]);							
Super User

Please post it at OR forum .

Calcite | Level 5 84
Calcite | Level 5

Ksharp..can u please share the link of the OR forum here?


Tourmaline | Level 20
@Ksharp: as Super User, you have the power to move it there 🙂
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