Add simple functionality for filling diagonal with the same matrix

[thomasgudjonwright]

Maybe this is unnecessary, or maybe there is an easy way to do this already, but could it be beneficial to add functionality like this?

julia> x = rand(2,2)
2×2 Matrix{Float64}:
 0.378402  0.484365
 0.799401  0.019679

julia> x_diag = BlockDiagonal(x, 2)
4×4 BlockDiagonal{Float64, Matrix{Float64}}:
 0.378402  0.484365  0.0       0.0
 0.799401  0.019679  0.0       0.0
 0.0       0.0       0.378402  0.484365
 0.0       0.0       0.799401  0.019679

julia> BlockDiagonal(x, 2) == BlockDiagonal([x, x])
true

So far the best way to do this at this point I have found is this:

julia> BlockDiagonal(FillArrays.fill(x,2))
4×4 BlockDiagonal{Float64, Matrix{Float64}}:
 0.378402  0.484365  0.0       0.0
 0.799401  0.019679  0.0       0.0
 0.0       0.0       0.378402  0.484365
 0.0       0.0       0.799401  0.019679

[mzgubic]

🤷 idk, I'd just do BlockDiagonal([x for _ in 1:3])

[ay111]

I want to suggest that you may consider adding a functionality of the form BlockDiagonal([(X1,m1), (X2, m2), . . . , (Xn, mn)]) such that it can be easier to form a block diagonal matrix with matrix X1, n1 times followed by X2, n2 times and so on. You may also consider a general form BlockDiagonal([(X1,m1,d1), (X2, m2, d2), . . . , (Xn, mn, dn)]) to form a block matrix that will place X1 in diagonal d1, n1 times then X2 in diagonal d2, n2 times and so on.