Hi,
I successfully build a lp model. Now i want to repeat the model several times and decrease one scalar (‘CAP’) in decrements of five till it reaches 30. I tried to implement a loop and an if statement but it doesnt work. Below I put the running model with the start scalar CAP of 60.
*Task
******
sets
I Set of customers incl. the depot /0*20/
;
alias(v,i,j);
parameter
d(i) Demand of customer i /0 0, 1 20, 2 10, 3 15, 4 10, 5 20, 6 15, 7 20, 8 10, 9 15, 10 10,
11 10, 12 15, 13 20, 14 10, 15 20, 16 10, 17 20, 18 15, 19 20, 20 10/
a(i) /0 0, 1 360, 2 360, 3 360, 4 360, 5 360, 6 480, 7 480, 8 480, 9 480, 10 480,
11 360, 12 360, 13 360, 14 360, 15 360, 16 480, 17 480, 18 480, 19 480, 20 480/
b(i) /0 0, 1 600, 2 600, 3 600, 4 600, 5 600, 6 720, 7 720, 8 720, 9 720, 10 720,
11 600, 12 600, 13 600, 14 600, 15 600, 16 720, 17 720, 18 720, 19 720, 20 720/
s(i) /0 0, 1 10, 2 5, 3 15, 4 20, 5 5, 6 10, 7 5, 8 15, 9 20, 10 5,
11 10, 12 5, 13 15, 14 20, 15 5, 16 10, 17 20, 18 15, 19 10, 20 20/
;
scalar
CAP Capacity of the trucks /60/
K Truck fleet size /10/
M large number /10000/
;
table
c(i,j) Costs between customer (node) i and customer (node) j
$ONDELIM
$INCLUDE Data_c.csv
$OFFDELIM
table
t(i,j)
$ONDELIM
$INCLUDE Data_t.csv
$OFFDELIM
;
binary variables
x(i,j) is 1 - if node j is served after node i (0 otherwise)
;
positive variable
u(i) Loading of a truck when leaving node i
w(i)
;
variable
F Objective function value (Total costs)
;
equations
of Objective function (minimises the total costs)
pred(j) every customer has only one predecessor node
succ(i) every customer has only one successor node
start every tour starts at the central warehouse
end every tour ends at the central warehouse
load(i,j) calculates the loading when leaving a node
loadres1(i) loading is at least as large as the demand at node i
loadres2(i) loading is at most as large as the capacity of the vehicle
loadres3(i)
loadres4(i)
load2(i,j)
;
of.. F =E= sum((i,j), c(i,j) * x(i,j));
pred(j)$(ord(j)>1).. sum(i, x(i,j)) =E= 1;
succ(i)$(ord(i)>1).. sum(j, x(i,j)) =E= 1;
start.. sum(j, x("0",j)) =E= K ;
end.. sum(i, x(i,"0")) =E= K ;
load(i,j)$(ord(i)>1 and ord(j)>1 and ord(i) <> ord(j)).. u(i) + d(j) - CAP * (1 - x(i,j)) =L= u(j) ;
loadres1(i)$(ord(i)>1).. d(i) =L= u(i) ;
loadres2(i)$(ord(i)>1).. u(i) =L= CAP ;
loadres3(i)$(ord(i)>1).. a(i) =L= w(i) ;
loadres4(i)$(ord(i)>1).. w(i) =L= b(i) ;
load2(i,j)$(ord(i)>1 and ord(j)>1 and ord(i) <> ord(j)).. w(i) + s(i) + t(i,j) - M * (1 - x(i,j)) =L= w(j) ;
model CVRP /all/ ;
option optcr = 0.0;
solve CVRP minimizing F using mip ;
display F.L, x.L, u.L, w.L ;
Thank you very much in advance for any help 