PuLP LP File Dummy Constraints

[Ilia Karmanov]

For some reason when I output my lp with pulp I notice dummy constraints:

_dummy: __dummy = 0

_C362: __dummy <= 1

..

_dummy: __dummy = 0

_C369: __dummy <= 1

I don't get these when I create the problem using gurobi-python API. However, my solution seems to be unaffected (I guess the dummy constraints are forced to 0 trivially) however I dont understand why they appear.

The constraint that causes this is not particularly special ... maybe I can try writing it to a text-file to see what I get:

for k, v in mydictionary.items():
    if len(v) > 1:
        for s in g[:-1]:
            model += pulp.lpSum(x[t, s] for tin v if sin compatible[mydf.loc[turn].Size]) <= 1

[Fernando Badilla Veliz]

Can't really answer without looking at the model itself, but normally some preprocessing is made discarding unused variables hence the dummies. (Here you can mess with the solver options)

You could complete the for loop for marking each combination of indices when the x variable is used or not. Something like printing everywhere when the complete clause is true and when the clause is false.

Pseudocode really bad written:

for k, v in mydictionary.items():
    if len(v) > 1:
        for s in g[:-1]:
            model += pulp.lpSum(x[t, s] for tin v if sin compatible[mydf.loc[turn].Size]) <= 1

for tin v if sin compatible[mydf.loc[turn].Size


print "using" k,v,t,s

this for need decomposition also...

else:

print "not using" k,v,t,s

Goodluck!

Fdo Bad Vel

+56 9 93099326

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[Rennan Chagas]

Hey guys!

I have the same problem here

there is a constraint set that gives me __dummy <= number constraints. I already printed variables, parameters and indices and everything looks ok

for v in vessellist:

if int(v.id) < len(Vessels)/2:

for k in routelist:

for t in range(k.freq):

prob += v.eta*Y[v.id][k.id][t] <= k.depart[t], 'Rdepart_'+str(v.id)+"_"+str(k.id)+"_"+str(t)

Here is a example of the output lp file

Rdepart_1_1_0: __dummy <= 17

Rdepart_1_1_1: __dummy <= 101

Rdepart_1_2_0: __dummy <= 76

Rdepart_1_2_1: __dummy <= 160

And this is what it should be

Rdepart_1_1_0: 0.0 Y_1_1_0 <= 17.0

Rdepart_1_1_1: 0.0 Y_1_1_1 <= 101.0

Rdepart_1_2_0: 0.0 Y_1_2_0 <= 76.0

Rdepart_1_2_1: 0.0 Y_1_2_1 <= 160.0

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