# JuMP broadcasting in @constraint involving expressions throws error

**URL:** <https://discourse.julialang.org/t/jump-broadcasting-in-constraint-involving-expressions-throws-error/82044>\
**Category:** Optimization (Mathematical)\
**Tags:** jump, optimization\
**Created:** [June 1, 2022, 10:11am UTC](https://discourse.julialang.org/t/jump-broadcasting-in-constraint-involving-expressions-throws-error/82044 "2022-06-01T10:11:51Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Shuhua](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/shuhua/32/27618_2.png) [@Shuhua](https://discourse.julialang.org/u/Shuhua)\
**Post date:** [June 1, 2022, 10:11am UTC](https://discourse.julialang.org/t/jump-broadcasting-in-constraint-involving-expressions-throws-error/82044/1 "2022-06-01T10:11:51Z")

</div>

An example is given below.

```julia
using JuMP
model = JuMP.Model()
@expression(model, x, zeros(AffExpr, 1, 4))
@expression(model, y, zeros(AffExpr, 2, 4))
@constraint(model, y .>= x) # A: OK
@constraint(model, x .<= y) # B: error

```

The above code B throws an error:

```julia
DimensionMismatch("destination axes (Base.OneTo(1), Base.OneTo(4)) are not compatible with source axes (Base.OneTo(2), Base.OneTo(4))")

```

However, if `x` and `y` are variable containers, then both code A and B are correct.  
Is broadcasting in `@constraint` involving expressions undirectional? (there is the so-called source and destination in the error info)

Any help is much appreciated. @odow

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [June 1, 2022, 7:48pm UTC](https://discourse.julialang.org/t/jump-broadcasting-in-constraint-involving-expressions-throws-error/82044/2 "2022-06-01T19:48:46Z")

</div>

That looks like a bug:

```julia
julia> model = JuMP.Model()
A JuMP Model
Feasibility problem with:
Variables: 0
Model mode: AUTOMATIC
CachingOptimizer state: NO_OPTIMIZER
Solver name: No optimizer attached.

julia> @expression(model, x, zeros(AffExpr, 1, 4))
1×4 Matrix{AffExpr}:
 0 0 0 0

julia> @expression(model, y, zeros(AffExpr, 2, 4))
2×4 Matrix{AffExpr}:
 0 0 0 0
 0 0 0 0

julia> @constraint(model, y .>= x) # A: OK
2×4 Matrix{ConstraintRef{Model, MathOptInterface.ConstraintIndex{MathOptInterface.ScalarAffineFunction{Float64}, MathOptInterface.GreaterThan{Float64}}, ScalarShape}}:
 0 ≥ 0.0 0 ≥ 0.0 0 ≥ 0.0 0 ≥ 0.0
 0 ≥ 0.0 0 ≥ 0.0 0 ≥ 0.0 0 ≥ 0.0

julia> @constraint(model, x .<= y)
ERROR: DimensionMismatch("destination axes (Base.OneTo(1), Base.OneTo(4)) are not compatible with source axes (Base.OneTo(2), Base.OneTo(4))")
Stacktrace:
 [1] throwdm(axdest::Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}}, axsrc::Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}})
   @ Base.Broadcast ./broadcast.jl:1060
 [2] copyto!
   @ ./broadcast.jl:972 [inlined]
 [3] copyto!
   @ ./broadcast.jl:936 [inlined]
 [4] broadcast!(op::typeof(MutableArithmetics.sub_mul), A::Matrix{AffExpr}, args::Matrix{AffExpr})
   @ MutableArithmetics ~/.julia/packages/MutableArithmetics/VLWSd/src/broadcast.jl:117
 [5] broadcast_fallback!
   @ ~/.julia/packages/MutableArithmetics/VLWSd/src/broadcast.jl:173 [inlined]
 [6] broadcast!!(::typeof(MutableArithmetics.sub_mul), ::Matrix{AffExpr}, ::Matrix{AffExpr})
   @ MutableArithmetics ~/.julia/packages/MutableArithmetics/VLWSd/src/broadcast.jl:145
 [7] macro expansion
   @ ~/.julia/packages/MutableArithmetics/VLWSd/src/rewrite.jl:294 [inlined]
 [8] macro expansion
   @ ~/.julia/dev/JuMP/src/macros.jl:823 [inlined]
 [9] top-level scope
   @ REPL[6]:1

```

In general though, that broadcasting could be confusing. You’re probably better to use explicit indexing:

```julia
@constraint(model, [i=1:2, j=1:4], x[1, j] <= y[i, j])

```

Edit: opened an issue: [Broadcasting mismatched expressions in constraint fails · Issue #158 · jump-dev/MutableArithmetics.jl · GitHub](https://github.com/jump-dev/JuMP.jl/issues/2997)