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CPLEX.jl

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CPLEX.jl is a wrapper for the IBM® ILOG® CPLEX® Optimization Studio.

CPLEX.jl has two components:

The C API can be accessed via CPLEX.CPXxx functions, where the names and arguments are identical to the C API. See the CPLEX documentation for details.

Affiliation

This wrapper is maintained by the JuMP community and is not officially supported by IBM. However, we thank IBM for providing us with a CPLEX license to test CPLEX.jl on GitHub. If you are a commercial customer interested in official support for CPLEX in Julia, let them know.

Getting help

If you need help, please ask a question on the JuMP community forum.

If you have a reproducible example of a bug, please open a GitHub issue.

License

CPLEX.jl is licensed under the MIT License.

The underlying solver is a closed-source commercial product for which you must purchase a license.

Free CPLEX licenses are available for academics and students.

Installation

CPLEX.jl requires CPLEX version 12.10, 20.1, or 22.1.

First, obtain a license of CPLEX and install CPLEX solver, following the instructions on IBM's website.

Once installed, set the CPLEX_STUDIO_BINARIES environment variable as appropriate and run Pkg.add("CPLEX"). For example:

# On Windows, this might be:
ENV["CPLEX_STUDIO_BINARIES"] = "C:\\Program Files\\CPLEX_Studio1210\\cplex\\bin\\x86-64_win\\"
# On OSX, this might be:
ENV["CPLEX_STUDIO_BINARIES"] = "/Applications/CPLEX_Studio1210/cplex/bin/x86-64_osx/"
# On Unix, this might be:
ENV["CPLEX_STUDIO_BINARIES"] = "/opt/CPLEX_Studio1210/cplex/bin/x86-64_linux/"

import Pkg
Pkg.add("CPLEX")

!!! note The exact path may differ. Check which folder you installed CPLEX in, and update the path accordingly.

Use with JuMP

Use CPLEX.jl with JuMP as follows:

using JuMP, CPLEX
model = Model(CPLEX.Optimizer)
set_attribute(model, "CPX_PARAM_EPINT", 1e-8)

MathOptInterface API

The CPLEX optimizer supports the following constraints and attributes.

List of supported objective functions:

List of supported variable types:

List of supported constraint types:

List of supported model attributes:

Options

Options match those of the C API in the CPLEX documentation.

Set options using JuMP.set_attribute:

using JuMP, CPLEX
model = Model(CPLEX.Optimizer)
set_attribute(model, "CPX_PARAM_EPINT", 1e-8)

Callbacks

CPLEX.jl provides a solver-specific callback to CPLEX:

using JuMP, CPLEX, Test

model = direct_model(CPLEX.Optimizer())
set_silent(model)

# This is very, very important!!! Only use callbacks in single-threaded mode.
MOI.set(model, MOI.NumberOfThreads(), 1)

@variable(model, 0 <= x <= 2.5, Int)
@variable(model, 0 <= y <= 2.5, Int)
@objective(model, Max, y)
cb_calls = Clong[]
function my_callback_function(cb_data::CPLEX.CallbackContext, context_id::Clong)
    # You can reference variables outside the function as normal
    push!(cb_calls, context_id)
    # You can select where the callback is run
    if context_id != CPX_CALLBACKCONTEXT_CANDIDATE
        return
    end
    ispoint_p = Ref{Cint}()
    ret = CPXcallbackcandidateispoint(cb_data, ispoint_p)
    if ret != 0 || ispoint_p[] == 0
        return  # No candidate point available or error
    end
    # You can query CALLBACKINFO items
    valueP = Ref{Cdouble}()
    ret = CPXcallbackgetinfodbl(cb_data, CPXCALLBACKINFO_BEST_BND, valueP)
    @info "Best bound is currently: $(valueP[])"
    # As well as any other C API
    x_p = Vector{Cdouble}(undef, 2)
    obj_p = Ref{Cdouble}()
    ret = CPXcallbackgetincumbent(cb_data, x_p, 0, 1, obj_p)
    if ret == 0
        @info "Objective incumbent is: $(obj_p[])"
        @info "Incumbent solution is: $(x_p)"
        # Use CPLEX.column to map between variable references and the 1-based
        # column.
        x_col = CPLEX.column(cb_data, index(x))
        @info "x = $(x_p[x_col])"
    else
        # Unable to query incumbent.
    end

    # Before querying `callback_value`, you must call:
    CPLEX.load_callback_variable_primal(cb_data, context_id)
    x_val = callback_value(cb_data, x)
    y_val = callback_value(cb_data, y)
    # You can submit solver-independent MathOptInterface attributes such as
    # lazy constraints, user-cuts, and heuristic solutions.
    if y_val - x_val > 1 + 1e-6
        con = @build_constraint(y - x <= 1)
        MOI.submit(model, MOI.LazyConstraint(cb_data), con)
    elseif y_val + x_val > 3 + 1e-6
        con = @build_constraint(y + x <= 3)
        MOI.submit(model, MOI.LazyConstraint(cb_data), con)
    end
end
MOI.set(model, CPLEX.CallbackFunction(), my_callback_function)
optimize!(model)
@test termination_status(model) == MOI.OPTIMAL
@test primal_status(model) == MOI.FEASIBLE_POINT
@test value(x) == 1
@test value(y) == 2

Annotations for automatic Benders' decomposition

Here is an example of using the annotation feature for automatic Benders' decomposition:

using JuMP, CPLEX

function add_annotation(
    model::JuMP.Model,
    variable_classification::Dict;
    all_variables::Bool = true,
)
    num_variables = sum(length(it) for it in values(variable_classification))
    if all_variables
        @assert num_variables == JuMP.num_variables(model)
    end
    indices, annotations = CPXINT[], CPXLONG[]
    for (key, value) in variable_classification
        for variable_ref in value
            push!(indices, variable_ref.index.value - 1)
            push!(annotations, CPX_BENDERS_MASTERVALUE + key)
        end
    end
    cplex = backend(model)
    index_p = Ref{CPXINT}()
    CPXnewlongannotation(
        cplex.env,
        cplex.lp,
        CPX_BENDERS_ANNOTATION,
        CPX_BENDERS_MASTERVALUE,
    )
    CPXgetlongannotationindex(
        cplex.env,
        cplex.lp,
        CPX_BENDERS_ANNOTATION,
        index_p,
    )
    CPXsetlongannotations(
        cplex.env,
        cplex.lp,
        index_p[],
        CPX_ANNOTATIONOBJ_COL,
        length(indices),
        indices,
        annotations,
    )
    return
end

# Problem

function illustrate_full_annotation()
    c_1, c_2 = [1, 4], [2, 3]
    dim_x, dim_y = length(c_1), length(c_2)
    b = [-2; -3]
    A_1, A_2 = [1 -3; -1 -3], [1 -2; -1 -1]
    model = JuMP.direct_model(CPLEX.Optimizer())
    set_optimizer_attribute(model, "CPXPARAM_Benders_Strategy", 1)
    @variable(model, x[1:dim_x] >= 0, Bin)
    @variable(model, y[1:dim_y] >= 0)
    variable_classification = Dict(0 => [x[1], x[2]], 1 => [y[1], y[2]])
    @constraint(model, A_2 * y + A_1 * x .<= b)
    @objective(model, Min, c_1' * x + c_2' * y)
    add_annotation(model, variable_classification)
    optimize!(model)
    x_optimal = value.(x)
    y_optimal = value.(y)
    println("x: $(x_optimal), y: $(y_optimal)")
end

function illustrate_partial_annotation()
    c_1, c_2 = [1, 4], [2, 3]
    dim_x, dim_y = length(c_1), length(c_2)
    b = [-2; -3]
    A_1, A_2 = [1 -3; -1 -3], [1 -2; -1 -1]
    model = JuMP.direct_model(CPLEX.Optimizer())
    # Note that the "CPXPARAM_Benders_Strategy" has to be set to 2 if partial
    # annotation is provided. If "CPXPARAM_Benders_Strategy" is set to 1, then
    # the following error will be thrown:
    # `CPLEX Error  2002: Invalid Benders decomposition.`
    set_optimizer_attribute(model, "CPXPARAM_Benders_Strategy", 2)
    @variable(model, x[1:dim_x] >= 0, Bin)
    @variable(model, y[1:dim_y] >= 0)
    variable_classification = Dict(0 => [x[1]], 1 => [y[1], y[2]])
    @constraint(model, A_2 * y + A_1 * x .<= b)
    @objective(model, Min, c_1' * x + c_2' * y)
    add_annotation(model, variable_classification; all_variables = false)
    optimize!(model)
    x_optimal = value.(x)
    y_optimal = value.(y)
    println("x: $(x_optimal), y: $(y_optimal)")
end