## Allocations.jl

Algorithms for fair item allocation.
Author mlhetland
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Updated Last
1 Year Ago
Started In
September 2021

# Allocations.jl

The Allocations package deals with the fair allocation of indivisible items to a set of agents. For some background on this topic, see, e.g., the Wikipedia entry on fair item allocation, or the surveys by Amanatidis et al. and Suksompong, on the unconstrained and constrained versions of the problem, respectively.

## Installation

To install the package, you can simply import it in the Julia REPL:

julia> using Allocations

Press enter at the resulting prompt to install both the package and its dependencies.

To install a more recent version than the released one, you can use the package manager directly. In the Julia REPL, press ] to enter the Pkg REPL, and then add the package directly from the source:

You can then import the module as before.

## Basic use

To specify an allocation problem instance, create a valuation profile:

julia> V = Profile([1 2 3; 2 3 1])
Additive{Matrix{Int64}} with 2 agents and 3 items:
1  2  3
2  3  1

Profile is an abstract class, and Profile(X::Matrix) is an alias for Additive(X). Once you have a valuation profile, you can use an allocation function (ones called alloc_...), e.g., for finding a maximum Nash welfare (MNW) allocation:

julia> res = alloc_mnw(V);

Note that the first time you call an allocation function, it may take some time to finish, because there's quite a lot of compilation going on behind the scenes. From then on, in the same REPL session, there will be much less overhead.

These functions take a Profile as input and return a named tuple with the field alloc referring to an Allocation:

julia> A = res.alloc
Allocation with 2 agents and 3 items:
1 => {3}
2 => {1, 2}

The bundles of each agent is available through the bundle function:

julia> bundle(A, 2)
Set{Int64} with 2 elements:
2
1

Bundles should not be modified directly, as the Allocation also maintains an inverse mapping, from items to agents. Rather, use the give! and deny! functions.

Some allocation functions may produce other results as well, such as properties of the allocation that are naturally computed as part of the allocation process. For the MNW case, the objective value (the Nash welfare, which is being maximized) is available as mnw:

julia> res.mnw
15.0

The allocation functions also permit a matrix argument as a shortcut, implicitly creating an Additive. For example, you can find a maximin share (MMS) allocation as follows:

julia> alloc_mms([1 1 2 3; 2 1 2 3]).alloc
Allocation with 2 agents and 4 items:
1 => {2, 3}
2 => {1, 4}

## Solver configuration

Several allocation functions use mixed-integer linear programming via JuMP. Depending on the choice of MIP solver, solving even moderately-sized instances may take a significant amount of time. Choosing a different solver (from the default HiGHS.Optimizer) may speed things up considerably. For example, with the appropriate license, one could use use Gurobi as follows:1

Allocations.conf.MIP_SOLVER = Gurobi.Optimizer

It is also possible to supply the Optimizer (or other optimizer factories, e.g., constructed using optimizer_with_attributes) as the solver keyword argument to the relevant allocation functions.

Normally, the MIP solvers will print out quite a lot of information about what they're doing. If you're not interested in this output, you can generally turn it off using some solver-specific flag, supplied to optimizer_with_attributes.2 This is also where you'd supply other parameters, e.g., indicating time limits, acceptable inaccuracies, etc. For example:3

Allocations.conf.MIP_SOLVER = optimizer_with_attributes(
Gurobi.Optimizer,
"LogToConsole" => 0,     # No console output
"TimeLimit" => 60,       # Finish within 60 seconds
"MipGap" => 0.05,        # Permit 5% suboptimality
)

If you're unable to get rid of the output using solver parameters, a simple solution is to just silence all output while allocating:

julia> redirect_stdout(devnull) do
alloc_mnw(V)
end

If that doesn't do the trick, you could add redirect_stderr as well.