# Function with array of matrices as input in Julia 0.5
**URL:** https://discourse.julialang.org/t/function-with-array-of-matrices-as-input-in-julia-0-5/1004
**Category:** General Usage
**Created:** [December 16, 2016, 9:11pm UTC](https://discourse.julialang.org/t/function-with-array-of-matrices-as-input-in-julia-0-5/1004 "2016-12-16T21:11:34Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@lanaperisa](https://discourse.julialang.org/u/lanaperisa)
#### Post date: [December 16, 2016, 9:11pm UTC](https://discourse.julialang.org/t/function-with-array-of-matrices-as-input-in-julia-0-5/1004/1 "2016-12-16T21:11:34Z")
Been struggling with something for a while. I use a lot of arrays of matrices so I wanted to create a typealias for it like this:
```julia
typealias MatrixCell{T<:Number} Array{Matrix{T},1}
```
This way I can easily create an array of matrices of predefined length, for example
```julia
A=MatrixCell(2); A[1]=rand(4,4);A[2]=rand(2,2);
```
However, if I define a function like this:
```julia
function test{T<:Number}(A::MatrixCell{T})
println(typeof(A));
end
```
calling
```julia
test(A)
```
gives following error:
```julia
ERROR: MethodError: no method matching test(::Array{Array{T<:Number,2},1})
Closest candidates are:
test{T<:Number}(::Array{Array{T<:Number,2},1}) at REPL[3]:2
```
Now this is really confusing, since the methods match.
I can work around by removing T\<:Number from both MatrixCell and function defintion, but then the function does not work with arrays defined as
```julia
B=[rand(4,3),rand(3,3)]
```
Any ideas? Thanks!
---
### Author:  [@mbauman](https://discourse.julialang.org/u/mbauman)
#### Post date: [December 16, 2016, 9:35pm UTC](https://discourse.julialang.org/t/function-with-array-of-matrices-as-input-in-julia-0-5/1004/2 "2016-12-16T21:35:41Z")
This is a corner-case of type-invariance with the current type system. You should find that it behaves as you expect if you give your `MatrixCell` a concrete element type:
```julia
A=MatrixCell{Float64}(2)
```
This is definitely tricky and I think it should be both less surprising and more obvious with the type-system revamp that’s slated for 0.6.
---
### Author:  [@lanaperisa](https://discourse.julialang.org/u/lanaperisa)
#### Post date: [December 16, 2016, 9:56pm UTC](https://discourse.julialang.org/t/function-with-array-of-matrices-as-input-in-julia-0-5/1004/3 "2016-12-16T21:56:11Z")
OK, thanks for the reply. I just realized I can remove T\<:Number from MatrixCell and the function and then define another method of the function to work with arrays defined as
```julia
B=[rand(4,3),rand(3,3)]
```
in the following way:
```julia
test{T<:Number}(A::Array{Matrix{T},1})=test(MatrixCell(A))
```
This way I have the function working for array of matrices defined both ways.
Sharing always helps 😉