Rob: here is the code that you had. i am having 2 questions (a) in the create data step, i was trying various options to print the distance between the customer and its assigned facility. One of the example, is fro Miami to Newark, where the distance should have been 1,268 (miles) but it gave me 3,493. I used Distance[i,j] to come up with this number. I also tried using GEODIST to calculate the distance between the final X and customers but it did not work either. (b) Is there a way to specify to the model to pick a facility that is no more than 500 miles or any prefixed number. I was thinking to have this constraint like this in NLP :- con radius{i in CUSTOMERS, j in FACILITIES}: Distance[i,j] <= 500; Will that be ok. I ran the model but it gave me same result as without the constraint "radius" %let m = 3;
proc optmodel;
set DIMS = 1..2;
set CUSTOMERS;
set FACILITIES = 1..&m;
num a {CUSTOMERS, DIMS};
num demand {CUSTOMERS};
read data cdata into CUSTOMERS=[_N_] {d in DIMS} <a[_N_,d]=col('a'||d)> demand;
num Xlb {d in DIMS} = min {i in CUSTOMERS} a[i,d];
num Xub {d in DIMS} = max {i in CUSTOMERS} a[i,d];
var X {FACILITIES, d in DIMS} >= Xlb[d] <= Xub[d];
var W {CUSTOMERS, FACILITIES} >= 0;
impvar Distance {i in CUSTOMERS, j in FACILITIES} =
sqrt(sum {d in DIMS}(a[i,d]-X[j,d])^2);
min Z = sum {i in CUSTOMERS, j in FACILITIES} W[i,j]*Distance[i,j];
con DemandCon {i in CUSTOMERS}:
sum {j in FACILITIES} W[i,j] = demand[i];
solve with nlp / ms;
print X;
put _OBJ_=;
/* post-processing: assign each customer to closest facility */
set CUSTOMERS_j {FACILITIES} init {};
num minDistance, argminDistance;
for {i in CUSTOMERS} do;
minDistance = constant('BIG');
argminDistance = .;
for {j in FACILITIES} do;
if minDistance > Distance[i,j] then do;
minDistance = Distance[i,j];
argminDistance = j;
end;
end;
for {j in FACILITIES} W[i,j] = 0;
W[i,argminDistance] = demand[i];
CUSTOMERS_j[argminDistance] = CUSTOMERS_j[argminDistance] union {i};
end;
put _OBJ_=;
/* post-processing: solve each facility separately */
min SingleFacilityObjective {j in FACILITIES} =
sum {i in CUSTOMERS_j[j]} demand[i]*Distance[i,j];
problem SingleFacilityProblem {j in FACILITIES} include
{d in DIMS} X[j,d]
SingleFacilityObjective[j];
for {j in FACILITIES} do;
put j=;
use problem SingleFacilityProblem[j];
solve;
end;
put (sum {j in FACILITIES} SingleFacilityObjective[j])=;
print X;
create data Xdata from [j]=FACILITIES {d in DIMS} <col('X'||d)=X[j,d].sol>;
create data assignments from [j i]={j in FACILITIES, i in CUSTOMERS_j[j]} W[i,j]
x1=a[i,1] y1=a[i,2] x2=X[j,1] y2=X[j,2];
quit; i
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