Negative signs in expressions

[joaquimg]

Here is a test:

using JuMP
function test1()
    model = Model()
    N = 1_000_000
    @variable(model, x[1:N])
    GC.gc()
    GC.gc()
    @time for i in 1:5
        @expression(model, sum(-1.0 * x[i] for i in 1:N))
    end
    GC.gc()
    GC.gc()
    @time for i in 1:5
        @expression(model, sum(-x[i] for i in 1:N))
    end
    GC.gc()
    GC.gc()
    @time for i in 1:5
        @expression(model, -sum(x[i] for i in 1:N))
    end
    return
end
test1()

Here are results:

  1.144432 seconds (235 allocations: 223.388 MiB)
  3.954068 seconds (35.00 M allocations: 2.900 GiB, 10.81% gc time)
  2.423065 seconds (475 allocations: 446.777 MiB)

I am actually very surprised that the second options is the slowest.
I first write it thinking it was the right way to do the third.

I think the action here is:

Have option 2 as fast as option 1.
Option 3 is seems a bit harder to detect and work with in a first glance.

[odow]

Second case is fixable:

julia> @macroexpand @expression(model, sum(-x[i] for i in 1:3))
quote
    #= REPL[284]:1 =#
    JuMP._valid_model(model, :model)
    begin
        #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros.jl:399 =#
        let model = model
            #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros.jl:400 =#
            begin
                #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros/@expression.jl:86 =#
                begin
                    #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros.jl:264 =#
                    var"#511###405" = begin
                            #= /Users/oscar/.julia/packages/MutableArithmetics/bmgkg/src/rewrite.jl:374 =#
                            let
                                #= /Users/oscar/.julia/packages/MutableArithmetics/bmgkg/src/rewrite.jl:375 =#
                                begin
                                    #= /Users/oscar/.julia/packages/MutableArithmetics/bmgkg/src/rewrite.jl:371 =#
                                    var"#513###406" = MutableArithmetics.Zero()
                                    for i = 1:3
                                        #= /Users/oscar/.julia/packages/MutableArithmetics/bmgkg/src/rewrite_generic.jl:307 =#
                                        var"#512###407" = (MutableArithmetics.operate!!)(*, -1, x[i])
                                        var"#513###406" = (MutableArithmetics.operate!!)(MutableArithmetics.add_mul, var"#513###406", var"#512###407")
                                    end
                                end
                                #= /Users/oscar/.julia/packages/MutableArithmetics/bmgkg/src/rewrite.jl:376 =#
                                var"#513###406"
                            end
                        end
                    #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros.jl:265 =#
                    var"#514###408" = (JuMP.flatten!)(var"#511###405")
                end
                #= /Users/oscar/.julia/packages/JuMP/CU7H5/src/macros/@expression.jl:89 =#
                JuMP._replace_zero(model, var"#514###408")
            end
        end
    end
end