# Between Matrix{Matrix{Any}} and Matrix{Any}
**URL:** https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534
**Category:** General Usage
**Tags:** question, arrays
**Created:** [January 13, 2022, 8:17am UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534 "2022-01-13T08:17:46Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@frydaydeep](https://discourse.julialang.org/u/frydaydeep)
#### Post date: [January 13, 2022, 8:17am UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534/1 "2022-01-13T08:17:46Z")
```julia
function ⊗(A::T,B::T) where T<:Array
[i*B for i in A]
end
a = ⊗(rand(2,2),rand(3,3))
typeof(a)
Matrix{Matrix{Float64}} (alias for Array{Array{Float64, 2}, 2})
```
I know:
```julia
a = kron(rand(2,2),rand(3,3))
```
But I’m trying to get something like:
```julia
reduce(hcat,[collect(1:3) for i in 1:3)
```
which works on a Vector{Vector{Any}} but not on Matrix{Matrix{Any}}.
I tried to play with function cat() and I failed.
I tried cartesian index and I failed.
I mean, it is how our minds treat a matrix right? we can ‘blockrize’ or ‘flatten’ a matrix with very little effort. Can I do that in Julia?
---
### Author:  [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [January 13, 2022, 8:22am UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534/2 "2022-01-13T08:22:02Z")
`hcat` only works for vectors AFAIK. You can flatten a matrix with `A[:]`, then cat it and finally use `reshape` to get it back into the shape you want. Maybe an easier way is using something like [https://github.com/JuliaArrays/BlockArrays.jl](https://github.com/JuliaArrays/BlockArrays.jl)
---
### Author:  [@frydaydeep](https://discourse.julialang.org/u/frydaydeep)
#### Post date: [January 13, 2022, 12:20pm UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534/3 "2022-01-13T12:20:21Z")
Pardon my English but by “flatten” I mean Matrix{Any}
However I figure something out:
```julia
function ⊗(A::T,B::T) where T<:Array
a = [i*B for i in A] # blocked
c = reduce(hcat,[vcat(i...) for i in eachcol(a)])# flatten
a,c
end
A = rand(20,20)
B = rand(30,30)
@btime ⊗(A,B)
@btime kron(A,B)
```
---
### Author:  [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)
#### Post date: [November 2, 2022, 7:14am UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534/4 "2022-11-02T07:14:01Z")
I don’t think it’s very efficient, but just to show Julia’s many possibilities …
```julia
hvcat(size(A),.*(A, [B])...)
```
```julia
reshape(vcat(.*(A, [B])...),size(A).*size(B))
reshape(reduce(vcat, A.*[B]), size(A).*size(B))
```
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [November 2, 2022, 9:28am UTC](https://discourse.julialang.org/t/between-matrix-matrix-any-and-matrix-any/74534/5 "2022-11-02T09:28:22Z")
I can’t recommend the package `TensorCast.jl` highly enough for this kind of array index wrangling:
```julia
A, B = rand(20,20), rand(30,30)
using TensorCast
@cast C[m⊗i,n⊗j] := A[i,j] * B[m,n]
C == kron(A,B) # true
```
In this case there is a built-in `kron` function available, but in most cases it is more complicated for regular users to find an effective solution.