Having nothing as an outcome using GLPK and JuMP

Specific Domains Optimization (Mathematical)
1

i have this piece of code for optimization:

using JuMP
using GLPK

function scan_maker(A)
    m= Model(GLPK.Optimizer)
    

    level = size(A, 2)
    v = zeros(Int, level)
    ub = zeros(Int, level)
    lb = zeros(Int, level)

    @variable(m, x[1:level])
    @constraint(m, con, A*x.>=0)

    function setc(a)
        set_normalized_rhs.(con, float.(a))
    end
    
    function scan(c::Channel)
        i = 1
        init = 1
        while i > 0
            if i >= init
                @objective(m, Max, x[i])
                res = JuMP.optimize!(m)
                if termination_status(m) == MOI.OPTIMAL || termination_status(m) == MOI.DUAL_INFEASIBLE
                    ub[i] = round(Int, getvalue(x[i]))
                    set_objective_sense(m, MOI.MIN_SENSE)
                    res = JuMP.optimize!(m)
                    @assert termination_status(m) == MOI.OPTIMAL || termination_status(m) == MOI.DUAL_INFEASIBLE
                    lb[i] = round(Int, getvalue(x[i]))

                    v[i] = lb[i]
                    init += 1
                else
                    @assert termination_status(m) == MOI.INFEASIBLE
                    i -= 1
                    continue
                end
            elseif v[i] < ub[i]
                v[i] += 1
            else
                set_upper_bound(x[i], Inf)
                set_lower_bound(x[i], -Inf)
                init -= 1
                i -= 1
                continue
            end

            if i >= level
                put!(c, v)
                continue
            else
                set_upper_bound(x[i], v[i])
                set_lower_bound(x[i], v[i])
                i += 1
            end
        end
        close(c)
    end
    
    return setc, scan
end

the code works quite well except for the first nested function setc when i call it it shows nothing in the output and i don’t know with what i should change set_normalized_rhs
because when i do this :

A=[2 2;1 1;4 3]
a=[2,3,7]
b, d= scan_maker(A)

b(a)

i get this

3-element Array{Nothing,1}:
 nothing
 nothing
 nothing
2

What do you expect b(a) to return?

You’re broadcasting a function (set_normalized_rhs) that returns nothing over three elements, so you get a vector of 3 nothings.

1 Like
5

What @odow is saying is that the result of of set_normalized_rhs is always nothing. Since setc returns the results of set_normalized_rhs, you get nothings. So your code needs to be changed in order to return something else. What do you want it to return?

1 Like
6

oh now i get it, well i was using on JuMP@0.18 this: model.linconstr.lb where lb is the lower bound, now i switched to set_normalized_rhs, so basically i’m expecting to get the lower bound.

1 Like
7

using on JuMP@0.18 this: model.linconstr.lb where lb is the lower bound, now i switched to set_normalized_rhs , so basically i’m expecting to get the lower bound according to the constraint

8

The lower bound will be a, because you’re setting it. Why do you need it returned from setc? You’re passing it in as an argument.