Hi

I’m currently trying to run a simple VRPTW (with 30 nodes) gams code. it has Big M in one the equations as u can see:

eq7 (arc1(i,f),k)… s1(f,k)=g=s1(i,k) + t1(i,f) ;

The value of big M extremely effects the solver performance, for example when I set M, 100000000(9 zeros), gams couldnt find a feasible solution withing 3000secs. but a big M with 10 zeros, worked and I could get a feasible solution. the point is it seems this big M,doesnt work with all data sets. so what should I do???

I found this: http://www.gams.com/solvers/cpxindic.htm

so I changed my code to this one:

eq7(arc1(i,f),k)… s1(f,k)=g=s1(i,k) + t1(i,f);

model vrpcd /cost,eq2,eq3,eq4,eq52,eq7,eq8,eq8a,eq91/;

vrpcd.reslim= 3000 ;

option mip= cplex;

file fcpx Cplex Option file / cplex.opt /;

putclose fcpx ‘indic eq7(arc1(i,f),k)$x1(i,f,k) 1’ ;

vrpcd.OptFile = 1;

solve vrpcd using mip minimizing z;

but then I get this error:

Row ‘eq7(1.7.a)’ infeasible, all entries at implied bounds.

No solution exists.

problem is integer infeasible

can anyone help me with this plz?

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