In Matlab:
>> A = [1 2; 3 4]
A =
1 2
3 4
>> save file_with_A
In Julia:
julia> using MAT
julia> file = matopen("file_with_A.mat")
MAT.MAT_v5.Matlabv5File(IOStream(<file file_with_A.mat>), false, #undef)
julia> read(file,"A")
2×2 Matrix{Float64}:
1.0 2.0
3.0 4.0
julia> close(file)