ConstraintSolver.jl

This package aims to be a constraint solver completely written in Julia. The concepts are more or less fully described on my blog OpenSourc.es. There is of course also the general user manual here which explains how to solve your model.

• Easily extendable
• Teaching/Learning about constraint programming

You can install this julia package using ] add ConstraintSolver or if you want to change code you might want to use ] dev ConstraintSolver.

You can easily use this package with the same modeling package as you might be used to for solving (non)linear problems in Julia: JuMP.jl.

using JuMP

grid = [6 0 2 0 5 0 0 0 0;
        0 0 0 0 0 3 0 4 0;
        0 0 0 0 0 0 0 0 0;
        4 3 0 0 0 8 0 0 0;
        0 1 0 0 0 0 2 0 0;
        0 0 0 0 0 0 7 0 0;
        5 0 0 2 7 0 0 0 0;
        0 0 0 0 0 0 0 8 1;
        0 0 0 6 0 0 0 0 0]

using ConstraintSolver
# define a shorter name ;)
const CS = ConstraintSolver

# creating a constraint solver model and setting ConstraintSolver as the optimizer.
m = Model(CS.Optimizer) 
# define the 81 variables
@variable(m, 1 <= x[1:9,1:9] <= 9, Int)
# set variables if fixed
for r=1:9, c=1:9
    if grid[r,c] != 0
        @constraint(m, x[r,c] == grid[r,c])
    end
end

for rc = 1:9
    @constraint(m, x[rc,:] in CS.AllDifferent())
    @constraint(m, x[:,rc] in CS.AllDifferent())
end

for br=0:2
    for bc=0:2
        @constraint(m, vec(x[br*3+1:(br+1)*3,bc*3+1:(bc+1)*3]) in CS.AllDifferent())
    end
end

optimize!(m)

# retrieve grid
grid = convert.(Int, JuMP.value.(x))

You can see a list of currently supported constraints in the docs. In general the solver works only with bounded discrete variables and supports these constraints

• linear constraints
• all different
• table
• indictoar
• reified
• boolean

A list of example problems can be found on the website by Håkan Kjellerstrand.

If you're interested in how the solver works you can checkout my blog opensourc.es. There are currently around 30 blog posts about the constraint solver and a new one is added about once per month.

I'm a MSc student in computer science so I don't have much knowledge on how constraint programming works but I'm keen to find out ;)

If you find a bug or improvement please open an issue or make a pull request. Additionally if you use the solver regularly or are interested in further development please checkout my Patreon page or click on the support button at the top of this website. ;)