# Push!() giving Method type error
**URL:** https://discourse.julialang.org/t/push-giving-method-type-error/76322
**Category:** New to Julia
**Tags:** question
**Created:** [February 12, 2022, 11:08pm UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322 "2022-02-12T23:08:33Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Brian\_Becsi](https://discourse.julialang.org/u/Brian_Becsi)
#### Post date: [February 12, 2022, 11:08pm UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/1 "2022-02-12T23:08:33Z")
I am getting a Method error, specifically a type conversion error, specifically Array{Float64,2} to type Int64.
I don’t understand types very well yet, and definitely don’t understand why push!() would be trying to convert to an integer. Here’s my code, “principal\_minor.jl” is working well in the REPL.
```julia
using Symbolics
using Latexify
using SymPy
using LinearAlgebra
include("principal_minor.jl")
function characteristic_polynomial(A)
z = size(A)
n = z[1]
p = [1]
for i = 1:n
p_0 = (-1)^i*sum(principal_minor(A,i))
#print(typeof(p_0))
push!(p, p_0)
end
return p
end
```
I’ve tried casting a few of the arguments but didn’t work. Any feedback is appreciated, especially quick tips about dealing with these type errors as they have been the roadblock I come across the most.
Thanks for reading!
---
### Author:  [@oheil](https://discourse.julialang.org/u/oheil)
#### Post date: [February 12, 2022, 11:34pm UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/2 "2022-02-12T23:34:33Z")
p is of type Vector{Int} and you try to push! something like a Array{Float64,2} (p\_0) into this array.
```julia
julia> p = [1]
1-element Vector{Int64}:
1
```
Your code is not a MWE (minimal working example) so it’s not clear what p\_0 is.
What is the output of `print(typeof(p_0))`?
For now a naiv solution can be not to initialize `p` as you do it, but e.g.:
```julia
function characteristic_polynomial(A)
z = size(A)
n = z[1]
for i = 1:n
p_0 = (-1)^i*sum(principal_minor(A,i))
if ! @isdefined p
p=Array{typeof(p_0)}(undef,0)
end
push!(p, p_0)
end
return p
end
```
This assumes that the type of p\_0 is always the same.
---
### Author:  [@Brian\_Becsi](https://discourse.julialang.org/u/Brian_Becsi)
#### Post date: [February 13, 2022, 12:01am UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/3 "2022-02-13T00:01:16Z")
thanks. I will look into the details of your response and follow up.
---
### Author:  [@Brian\_Becsi](https://discourse.julialang.org/u/Brian_Becsi)
#### Post date: [February 13, 2022, 1:43am UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/4 "2022-02-13T01:43:17Z")
exactly as you said. I fixed it by changing `sum(A)` to `sum(sum(principal_subminor(A,i)))`.
while this works for arrays with entries that are matrices, I know it won’t work for tensors of higher dimension, though I feel like I could write a function to do so. regardless, not relevant in this characteristic polynomial computation at the moment.
thanks for the response.
### Edited that is, `sum(sum(principal_subminor(A,i))`
---
### Author:  [@lawless-m](https://discourse.julialang.org/u/lawless-m)
#### Post date: [February 13, 2022, 8:01am UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/5 "2022-02-13T08:01:41Z")
small suggestion
```julia
z = size(A)
n = z[1]
for i = 1:n
```
can become
`for i in 1:size(A, 1)`
---
### Author:  [@gustaphe](https://discourse.julialang.org/u/gustaphe)
#### Post date: [February 13, 2022, 8:52am UTC](https://discourse.julialang.org/t/push-giving-method-type-error/76322/6 "2022-02-13T08:52:07Z")
If you want there’s always the option of playing the broadcasting game:
```julia
p = (-1).^(1:size(A, 1)) .* sum.(principal_minor.(Ref(A), 1:size(A, 1)))
```