# Plotting function returning complex vector

**URL:** <https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393>\
**Category:** New to Julia\
**Tags:** plotting, vector, complex-numbers\
**Created:** [July 2, 2025, 3:25am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393 "2025-07-02T03:25:18Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![rokke](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rokke/32/222691_2.png) [@rokke](https://discourse.julialang.org/u/rokke)\
**Post date:** [July 2, 2025, 3:25am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/1 "2025-07-02T03:25:18Z")

</div>

I have some functions which each return a constant `n` number of complex values, and would like to plot one as a series of lines on the complex plane. if I do something like  
`plot(real.([f.(0.1:.1:5)...;;]'),-imag.([f.(0.1:.1:5)...;;]'))`  
it technically does give me what I want, but then you lose the vertical axis being labeled as imaginary and the code is also kinda ugly. is there some way I can change the type of the functions or the call to get something more like `plot(f, 0.1:.1:5)`?

---

<div class="post-metadata">

**Author:** ![Sevi](https://avatars.discourse-cdn.com/v4/letter/s/c67d28/32.png) [@Sevi](https://discourse.julialang.org/u/Sevi)\
**Post date:** [July 2, 2025, 5:10am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/2 "2025-07-02T05:10:35Z")

</div>

Here are some loose suggestions:

- Add the labels manually `plot(...; xlabel="Re(z)", ylabel="Im(z)")`
- Just extract the individual vectors of complex numbers and put it as single argument into individual `plot!` calls (that will draw the curve in the complex plane with automatic axis labels).
- Write a custom plot function that does the above (this is probably what I would go for, since it also avoids calling the function `f` twice. Something like

```julia
function plot_complex_vector(f, u; kwargs...)
    results = f.(u)
    ...
    plot(...; kwargs...)
end

```

- Write a [plot recipe](https://docs.juliaplots.org/latest/recipes/) which is basically a function like the one above, but has a bit more standardized handling of extra kwargs etc. but also more overhead to write.

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [July 2, 2025, 5:45am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/3 "2025-07-02T05:45:28Z")

</div>

Wrangling data into larger arrays of the right dimensions in one-liners is always going to look a bit ugly and involve weird tricks like `-imag...'` for brevity. Sometimes a loop (that does more or less what Sevi suggests) is clearer.

---

<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [July 2, 2025, 7:48am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/4 "2025-07-02T07:48:57Z")

</div>

What is the problem when using Plots.jl with:

```julia
t = 0.1:0.1:5
plot(f.(t))

# or if you need the conjugate:
plot(conj(f.(t)))

```

---

<div class="post-metadata">

**Author:** ![rokke](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rokke/32/222691_2.png) [@rokke](https://discourse.julialang.org/u/rokke)\
**Post date:** [July 2, 2025, 7:58am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/5 "2025-07-02T07:58:17Z")

</div>

plot doesn’t seem to like that (`roots()` has same return type as my functions):

```julia
julia> using Plots, PolynomialRoots

julia> f(x) = roots([1,2,3,x])
f (generic function with 1 method)

julia> plot(f.(.1:.1:5))
ERROR: MethodError: no method matching isless(::Float64, ::ComplexF64)
The function `isless` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  isless(::Missing, ::Any)
   @ Base missing.jl:87
  isless(::Any, ::Missing)
   @ Base missing.jl:88
  isless(::AbstractFloat, ::SparseConnectivityTracer.GradientTracer)
   @ SparseConnectivityTracer ~/.julia/packages/SparseConnectivityTracer/YYCo5/src/overloads/gradient_tracer.jl:165
  ...

Stacktrace:
  [1] min(x::ComplexF64, y::Float64)
    @ Base ./operators.jl:499
  [2] expand_extrema!
    @ ~/.julia/packages/Plots/uiCPf/src/axes.jl:425 [inlined]
  [3] #113
    @ ~/.julia/packages/Plots/uiCPf/src/axes.jl:444 [inlined]
  [4] foreach
    @ ./abstractarray.jl:3187 [inlined]
  [5] expand_extrema!(axis::Plots.Axis, v::Vector{ComplexF64})
    @ Plots ~/.julia/packages/Plots/uiCPf/src/axes.jl:444
  [6] expand_extrema!(sp::Plots.Subplot{Plots.GRBackend}, plotattributes::RecipesPipeline.DefaultsDict)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/axes.jl:479
  [7] _expand_subplot_extrema(sp::Plots.Subplot{Plots.GRBackend}, plotattributes::RecipesPipeline.DefaultsDict, st::Symbol)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/pipeline.jl:433
  [8] add_series!(plt::Plots.Plot{Plots.GRBackend}, plotattributes::RecipesPipeline.DefaultsDict)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/pipeline.jl:376
  [9] _process_seriesrecipe(plt::Any, plotattributes::Any)
    @ RecipesPipeline ~/.julia/packages/RecipesPipeline/BGM3l/src/series_recipe.jl:46
 [10] _process_seriesrecipes!(plt::Any, kw_list::Any)
    @ RecipesPipeline ~/.julia/packages/RecipesPipeline/BGM3l/src/series_recipe.jl:27
 [11] recipe_pipeline!(plt::Any, plotattributes::Any, args::Any)
    @ RecipesPipeline ~/.julia/packages/RecipesPipeline/BGM3l/src/RecipesPipeline.jl:99
 [12] _plot!(plt::Plots.Plot, plotattributes::Any, args::Any)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/plot.jl:223
 [13] plot(args::Any; kw...)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/plot.jl:102
 [14] plot(args::Any)
    @ Plots ~/.julia/packages/Plots/uiCPf/src/plot.jl:93
 [15] top-level scope
    @ REPL[3]:1

```

I’m currently stumbling my way through writing a plot recipe, so should prob mark Sevi’s answer as solution instead of just hearting it; but I’m obviously still open to other solutions if people want to throw them at me

---

<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [July 2, 2025, 8:30am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/6 "2025-07-02T08:30:11Z")

</div>

> [@rokke](#):
>
> return a constant `n` number of complex values

The example doesn’t provide a vector of n-complex numbers, but a vector of vectors of complex numbers.  
The following would plot all the roots:

```julia-auto
scatter(reduce(vcat, f.(0.1:0.1:5)))

```

---

<div class="post-metadata">

**Author:** ![rokke](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rokke/32/222691_2.png) [@rokke](https://discourse.julialang.org/u/rokke)\
**Post date:** [July 2, 2025, 8:33am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/7 "2025-07-02T08:33:14Z")

</div>

the function itself just returns a vector of complex numbers; the vector of vectorness comes from using the `.` to distribute through the range

---

<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [July 2, 2025, 8:34am UTC](https://discourse.julialang.org/t/plotting-function-returning-complex-vector/130393/8 "2025-07-02T08:34:02Z")

</div>

Yeah, of course.