Errors

When an MOI call fails on a model, precise errors should be thrown when possible instead of simply calling error with a message. The docstrings for the respective methods describe the errors that the implementation should thrown in certain situations. This error-reporting system allows code to distinguish between internal errors (that should be shown to the user) and unsupported operations which may have automatic workarounds.

When an invalid index is used in an MOI call, an InvalidIndex should be thrown:

When an invalid result index is used to retrieve an attribute, a ResultIndexBoundsError should be thrown:

MathOptInterface.ResultIndexBoundsErrorType
struct ResultIndexBoundsError{AttrType} <: Exception
    attr::AttrType
    result_count::Int
end

An error indicating that the requested attribute attr could not be retrieved, because the solver returned too few results compared to what was requested. For instance, the user tries to retrieve VariablePrimal(2) when only one solution is available, or when the model is infeasible and has no solution.

See also: check_result_index_bounds.

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As discussed in JuMP mapping, for scalar constraint with a nonzero function constant, a ScalarFunctionConstantNotZero exception may be thrown:

Some VariableIndex constraints cannot be combined on the same variable:

As discussed in AbstractCallback, trying to get attributes inside a callback may throw:

MathOptInterface.OptimizeInProgressType
struct OptimizeInProgress{AttrType<:AnyAttribute} <: Exception
    attr::AttrType
end

Error thrown from optimizer when MOI.get(optimizer, attr) is called inside an AbstractCallback while it is only defined once optimize! has completed. This can only happen when is_set_by_optimize(attr) is true.

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Trying to submit the wrong type of AbstractSubmittable inside an AbstractCallback (e.g., a UserCut inside a LazyConstraintCallback) will throw:

The rest of the errors defined in MOI fall in two categories represented by the following two abstract types:

MathOptInterface.NotAllowedErrorType
NotAllowedError <: Exception

Abstract type for error thrown when an operation is supported but cannot be applied in the current state of the model.

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The different UnsupportedError and NotAllowedError are the following errors:

MathOptInterface.SetAttributeNotAllowedType
struct SetAttributeNotAllowed{AttrType} <: NotAllowedError
    attr::AttrType
    message::String # Human-friendly explanation why the attribute cannot be set
end

An error indicating that the attribute attr is supported (see supports) but cannot be set for some reason (see the error string).

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MathOptInterface.AddVariableNotAllowedType
struct AddVariableNotAllowed <: NotAllowedError
    message::String # Human-friendly explanation why the attribute cannot be set
end

An error indicating that variables cannot be added to the model.

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MathOptInterface.UnsupportedConstraintType
struct UnsupportedConstraint{F<:AbstractFunction, S<:AbstractSet} <: UnsupportedError
    message::String # Human-friendly explanation why the attribute cannot be set
end

An error indicating that constraints of type F-in-S are not supported by the model, i.e. that supports_constraint returns false.

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MathOptInterface.AddConstraintNotAllowedType
struct AddConstraintNotAllowed{F<:AbstractFunction, S<:AbstractSet} <: NotAllowedError
    message::String # Human-friendly explanation why the attribute cannot be set
end

An error indicating that constraints of type F-in-S are supported (see supports_constraint) but cannot be added.

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MathOptInterface.ModifyConstraintNotAllowedType
struct ModifyConstraintNotAllowed{F<:AbstractFunction, S<:AbstractSet,
                                  C<:AbstractFunctionModification} <: NotAllowedError
    constraint_index::ConstraintIndex{F, S}
    change::C
    message::String
end

An error indicating that the constraint modification change cannot be applied to the constraint of index ci.

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MathOptInterface.ModifyObjectiveNotAllowedType
struct ModifyObjectiveNotAllowed{C<:AbstractFunctionModification} <: NotAllowedError
    change::C
    message::String
end

An error indicating that the objective modification change cannot be applied to the objective.

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MathOptInterface.DeleteNotAllowedType
struct DeleteNotAllowed{IndexType <: Index} <: NotAllowedError
    index::IndexType
    message::String
end

An error indicating that the index index cannot be deleted.

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MathOptInterface.SubmitNotAllowedType
struct SubmitNotAllowed{SubmitTyp<:AbstractSubmittable} <: NotAllowedError
    sub::SubmitType
    message::String # Human-friendly explanation why the attribute cannot be set
end

An error indicating that the submittable sub is supported (see supports) but cannot be added for some reason (see the error string).

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Note that setting the ConstraintFunction of a VariableIndex constraint is not allowed: