# In-place SciMLOperators

**URL:** <https://discourse.julialang.org/t/in-place-scimloperators/130457>\
**Category:** Performance\
**Tags:** question, sciml, scmlop\
**Created:** [July 3, 2025, 5:19pm UTC](https://discourse.julialang.org/t/in-place-scimloperators/130457 "2025-07-03T17:19:02Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![fdekerme](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fdekerme/32/43574_2.png) [@fdekerme](https://discourse.julialang.org/u/fdekerme)\
**Post date:** [July 3, 2025, 5:19pm UTC](https://discourse.julialang.org/t/in-place-scimloperators/130457/1 "2025-07-03T17:19:02Z")

</div>

Hello 😀,  
Can anyone tell me more about SciMLOperators.jl’s in-place operations?

```julia
using SciMLOperators
using BenchmarkTools

function Afunc!(w,v,u,p,t)
    w[1] = -2v[1] + v[2]
    for i in 2:4
        w[i] = v[i-1] - 2v[i] + v[i+1]
    end
    w[5] = v[4] - 2v[5]
    nothing
end

function Afunc!(v,u,p,t)
    w = zeros(5)
    Afunc!(w,v,u,p,t)
    w
end

mfopA = FunctionOperator(Afunc!, zeros(5), zeros(5), isinplace=true, outofplace=false, isconstant=true, islinear=true)
res = zeros(5)
v = rand(5)
@btime mfopA * v
@btime mul!(res, mfopA, v)
@btime res = mfopA(v, nothing, nothing, nothing)

```

give the following results:

```julia
julia> @btime mfopA * v
  26.439 ns (2 allocations: 96 bytes)
5-element Vector{Float64}:
  0.11998935724715909
 -0.8311223582350354
  0.462012816005153
 -0.0787003727323099
  0.05822953891971461

julia> @btime mul!(res, mfopA, v)
  13.179 ns (0 allocations: 0 bytes)
5-element Vector{Float64}:
  0.11998935724715909
 -0.8311223582350354
  0.462012816005153
 -0.0787003727323099
  0.05822953891971461

julia> @btime res = mfopA(v, nothing, nothing, nothing)
  30.402 ns (3 allocations: 272 bytes)
5-element Vector{Float64}:
  0.11998935724715909
 -0.8311223582350354
  0.462012816005153
 -0.0787003727323099
  0.05822953891971461

```

So the only in-place non allocating version is `mul!(res, mfopA, v)`.  
My questions are:

- Why/when should I indicate `isinplace=true` in the FunctionOperator definition?
- If I am not wrong, it is stated [here](https://docs.sciml.ai/SciMLOperators/stable/interface/#SciMLOperators.AbstractSciMLOperator) that `v_mat = F(u_mat, p, t) # == mul!(v_mat, F, u_mat)`, so why it is not the case in my example?
- I don’t get the point with `cache_operator` function. When should I use it?

Thanks a lot!  
fdekerm