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# ColgenInstance:get(++What, -Value)

Obtain global problem information.
*What*
- Specification for information wanted (atom)
*Value*
- Returned value of What

## Description

Retrieve information about solver constraints and results, for the
colgen instance ColgenInstance. What can take one of the following values:

`dual(+Id)`
- Returns the floating-point value of the
current dual value for the constraint having identifier Id. See
also
`sp_obj` below.

`sp_obj(+Id)`
- Returns the sub problem objective terms currently associated
associated with the constraint having identifier Id. This will
be a term
`Val*Var` where Val is the current dual value
for the constraint as also returned by
`ColgenInstance:get(dual(Id), Val)` and Var is the
subproblem variable in the implicit sum term of the
constraint. It is the users responsibility to get all relevant
terms of the current cost function and ensure that subproblem
solutions posted to the colgen instance have a non-negative
cost.

`vars`
- Returns a list of all variables currently
associated with the colgen instance
`ColgenInstance`.

`non_zero_vars`
- Returns a list of all variables currently associated with
the colgen instance
`ColgenInstance` that have a non-zero
optimal solution. This may be more efficient than retrieving all
problem variables after solution, since very many variables can
be generated and most will have a zero value in the optimal
solution.

`frac_vars`
- Returns a list of all variables currently associated with
the colgen instance
`ColgenInstance` that have a
fractional optimal solution. This is intended for use primarily
in user-defined problem branching predicates.