Removing a constraint in CP-SAT

[Emmanuel Seve]

Hi all,

Is there a command to remove some constraints after the running the solver and re-run the same solver ?

Or the only possibility is to create a new solver ?

Emmanuel

[Laurent Perron]

get the underlying protobuf from the constraint object and call Clear()/clear() on it.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[christoph...@ksb.com]

For certain types of constraints, you can add a clause to the constraint with the "OnlyEnforceIf" function and provide a parameter that is false, or can be made false with another constraint you add, to deactivate the first constraint. This does not work for all types of contraints, however; the AllowedAssigments and ForbiddenAssignments are among those for which it does not work.

[Emmanuel Seve]

Thanks Laurent and Christoph

I think the first solution suit more to my case.

I have seen this example :

# 2. delete a == b # 

assuming that you did a_eq_b = model.Add(a == b) a_eq_b.Proto().Clear()

It is what you mean Laurent ?

a_eq_b should be declared somehow , right ? how ?

what to write a the beginning of the declaration of the constraint ?

"constraint_type"  a_eq_b = model.Add(a == b);

constraint_type = ?

[Laurent Perron]

look at the API

Python: https://google.github.io/or-tools/python/ortools/sat/python/cp_model.html#CpModel.Add

C++: https://google.github.io/or-tools/cpp_sat/classoperations__research_1_1sat_1_1_cp_model_builder.html#aac1d593654ac2c9e311b7337b702216b

Java: https://google.github.io/or-tools/javadoc/com/google/ortools/sat/CpModel.html#addEquality(com.google.ortools.sat.LinearExpr,long)

C#: https://google.github.io/or-tools/dotnet/classGoogle_1_1OrTools_1_1Sat_1_1CpModel.html#aeae42d5e9a6a0fc4a0b12ed903c071a6

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Emmanuel Seve]

Thanks .

I understood that the type is Constraint. So i wrote something like this:

Constraint  a_eq_b = model.Add(a == b); // (In Java)

Which sounds logical for me.

But i get the compilation error message :

cannot find symbol [ERROR]   symbol:   class Constraint

Something missing ?

[Laurent Perron]

using/import ?

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Emmanuel Seve]

Indeed, the compilation error disappear if i add :

import com.google.ortools.sat.Constraint;

[Emmanuel Seve]

But after when i tried to remove a constraint, the name of the constraint is not known

i tried :

Elim2.Proto().Clear();

model.Elim2.Proto().Clear();

model.Constraint.Elim2.Proto().Clear();

model.constraint.Elim2.Proto().Clear();

nothing works

[Emmanuel Seve]

Elim2 is the naùme of my constraint

Constraint Elim2 = model.addLessThan(LinearExpr.scalProd(FT_elim2,CoeffFT2),N_U);

[Laurent Perron]

what does it mean the name is not known?

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Emmanuel Seve]

cannot find symbol
[ERROR]   symbol:   variable Elim2
[ERROR]   location: variable model of type com.google.ortools.sat.CpModel

[Emmanuel Seve]

The variable Elim2 was not created in my program. 

But i still have a compilation errors even if the constraint Elim2 exists

Elim2.Proto().Clear(); => with or without capital letters : 

cannot find symbol [ERROR]   symbol:   method Proto()  (same with the method Clear if i remove .Proto()