# Encountering Method error when using abs2 function on a Complex{Num}

**URL:** <https://discourse.julialang.org/t/encountering-method-error-when-using-abs2-function-on-a-complex-num/115341>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [June 7, 2024, 3:34pm UTC](https://discourse.julialang.org/t/encountering-method-error-when-using-abs2-function-on-a-complex-num/115341 "2024-06-07T15:34:40Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [June 7, 2024, 3:59pm UTC](https://discourse.julialang.org/t/encountering-method-error-when-using-abs2-function-on-a-complex-num/115341/2 "2024-06-07T15:59:40Z")

</div>

The issue is not with `abs2`. From the stacktrace, we have the lines

```julia
  [1] convert(::Type{Float64}, x::Num)
    @ Base .\number.jl:7
  [2] setindex!(A::Vector{Float64}, x::Num, i1::Int64)
    @ Base .\array.jl:1021

```

We see here that we are attempting to store a `Num` into a `Vector{Float64}` (via `setindex!`, which is used for `x[i] = v` syntax). To do this, we see that to do this we attempt to convert a `Num` to a `Float64` so that we can store it, but the `MethodError` indicates this operation tries `Float64(::Num)` which is not defined.

A MWE is

```julia
using Symbolics
x = zeros(Float64, 1)
v = Num(1.0)
x[1] = v # MethodError

```

We need to tell the system how to do this conversion. [The docs](https://symbolics.juliasymbolics.org/stable/getting_started/#Simplification-and-Substitution) indicate that `Symbolics.value` can be used to extract the value from a `Num`.

So a fix is to instead use

```julia
x[1] = Symbolics.value(v)

```

* * *

In general, try not to post big code for small problems. You should attempt to [localize the problem and create a small example](https://discourse.julialang.org/t/please-read-make-it-easier-to-help-you/14757) showing the error (this can be difficult initially but gets easier the more familiar you become with the language). I provide an example of doing this above.

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_[View the full topic](https://discourse.julialang.org/t/encountering-method-error-when-using-abs2-function-on-a-complex-num/115341)._