# Can I extend other functions to make it compatible with Convex.jl (element-wise operation)

**URL:** <https://discourse.julialang.org/t/can-i-extend-other-functions-to-make-it-compatible-with-convex-jl-element-wise-operation/52565>\
**Category:** Optimization (Mathematical)\
**Tags:** optimization\
**Created:** [December 29, 2020, 10:15am UTC](https://discourse.julialang.org/t/can-i-extend-other-functions-to-make-it-compatible-with-convex-jl-element-wise-operation/52565 "2020-12-29T10:15:22Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![iHany](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ihany/32/18151_2.png) [@iHany](https://discourse.julialang.org/u/iHany)\
**Post date:** [December 29, 2020, 10:15am UTC](https://discourse.julialang.org/t/can-i-extend-other-functions-to-make-it-compatible-with-convex-jl-element-wise-operation/52565/1 "2020-12-29T10:15:22Z")

</div>

I’m using [Convex.jl](https://jump.dev/Convex.jl/stable/) for convex optimisation.

When constructing a function that I need to optimise, I used to extend methods of Convex to make it compatible with other functions, for example,

```julia
# extend Convex method
function Convex.pos(x::Array)
    return max.(x, 0.0)
end

```

Then, `pos(x)` can also be used as `relu` in [Flux](https://fluxml.ai/Flux.jl/stable/).

I wonder if it’s possible to extend “other functions” for this purpose and apply to element-wise operations. For example,

```julia
function Flux.relu(x::Convex.Variable)
    # blahblah...
end

```

and

```julia
relu.(x) # x: array

```

My simple test seems not work:

```julia
julia> function Flux.relu(x::Convex.Variable)
           return pos(x)
       end

julia> x = Variable(3)
Variable
size: (3, 1)
sign: real
vexity: affine
id: 451…306

julia> Flux.relu(x)
max (convex; positive)
├─ 3-element real variable (id: 451…306)
└─ 0

julia> Flux.relu.(x)
ERROR: MethodError: no method matching zero(::Convex.IndexAtom)
Closest candidates are:
  zero(::Type{Pkg.Resolve.VersionWeight}) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/versionweights.jl:15
  zero(::Type{Pkg.Resolve.FieldValue}) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Pkg/src/Resolve/fieldvalues.jl:38
  zero(::Type{ModelingToolkit.TermCombination}) at /home/jinrae/.julia/packages/ModelingToolkit/1qEYb/src/linearity.jl:67
  ...
Stacktrace:
 [1] relu(::Convex.IndexAtom) at /home/jinrae/.julia/packages/NNlib/2Wxlq/src/activation.jl:63
 [2] _broadcast_getindex_evalf at ./broadcast.jl:648 [inlined]
 [3] _broadcast_getindex at ./broadcast.jl:621 [inlined]
 [4] getindex at ./broadcast.jl:575 [inlined]
 [5] copy at ./broadcast.jl:876 [inlined]
 [6] materialize(::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1},Nothing,typeof(relu),Tuple{Array{Any,1}}}) at ./broadcast.jl:837
 [7] top-level scope at REPL[12]:1

```