No method for multiplying compatible BlockSkyLineMatrix and BandedMatrix

[TSGut]

Matrix multiplication is apparently not currently defined for BlockSkyLineMatrix and BandedMatrix even when dimensions should be compatible (i.e m x n array times n x k array).

Not entirely sure if this belongs in BandedMatrices or BlockBandedMatrices but I tend towards the latter so I'll put this here for now.

Here's a simple snippet that reproduces the error:

using BandedMatrices, BlockBandedMatrices

# generate some simple arrays
function M1(N::Integer)
    M = BlockBandedMatrix(Zeros(sum(1:N),N), (1:N,Ones{Int}(N)), (0,0))
        for n=1:N
            for j=1:n
                view(M, Block(n,n))[j,1] = 1.
            end
        end
    return M
end
function M2(N::Integer)
    M=BandedMatrix{Float64}(undef, (N, N), (0,1))
    for n=1:N-1
        M[n,n]=1.
        M[n,n+1]=1.
    end
    M[N,N]=1.
    return M
end

# works as intended, 55x10 * 10x10 * 10x1 array gives 55x1 array
N = 10
M1(N)
M2(N)
testvec = Ones(N,1)
M1(N)*(M2(N)*testvec)

# doesn't work:
M1(N)*M2(N)*testvec
# because this doesn't work
M1(N)*M2(N)

# also doesn't work:
M2(sum(1:N))*M1(N)*testvec
#while this does:
M2(sum(1:N))*(M1(N)*testvec)

[dlfivefifty]

Can you post the output?

[TSGut]

Sure, it gives a method error due to ambiguity. The first one I mentioned which doesn't work outputs

M1(N)*M2(N)
ERROR: MethodError: *(::BlockSkylineMatrix{Float64,Fill{Int64,1,Tuple{Base.OneTo{Int64}}},Fill{Int64,1,Tuple{Base.OneTo{Int64}}}}, ::BandedMatrix{Float64,Array{Float64,2},Base.OneTo{Int64}}) is ambiguous. Candidates:
  *(A::AbstractArray{T,2} where T, B::BandedMatrices.AbstractBandedMatrix, C...) in BandedMatrices at /home/timon/.julia/packages/LazyArrays/jsu0l/src/linalg/lazymul.jl:20
  *(A::BlockBandedMatrices.AbstractBlockBandedMatrix, B::AbstractArray{T,2} where T, C...) in BlockBandedMatrices at /home/timon/.julia/packages/LazyArrays/jsu0l/src/linalg/lazymul.jl:18
Possible fix, define
  *(::BlockBandedMatrices.AbstractBlockBandedMatrix, ::BandedMatrices.AbstractBandedMatrix, ::Vararg{Any,N} where N)

More or less the same for M2(sum(1:N))*M1(N)*testvec:

M2(sum(1:N))*M1(N)*testvec
ERROR: MethodError: *(::BandedMatrix{Float64,Array{Float64,2},Base.OneTo{Int64}}, ::BlockSkylineMatrix{Float64,Fill{Int64,1,Tuple{Base.OneTo{Int64}}},Fill{Int64,1,Tuple{Base.OneTo{Int64}}}}, ::Ones{Float64,2,Tuple{Base.OneTo{Int64},Base.OneTo{Int64}}}) is ambiguous. Candidates:
  *(A::AbstractArray{T,2} where T, B::BlockBandedMatrices.AbstractBlockBandedMatrix, C...) in BlockBandedMatrices at /home/timon/.julia/packages/LazyArrays/jsu0l/src/linalg/lazymul.jl:20
  *(A::BandedMatrices.AbstractBandedMatrix, B::AbstractArray{T,2} where T, C...) in BandedMatrices at /home/timon/.julia/packages/LazyArrays/jsu0l/src/linalg/lazymul.jl:18
Possible fix, define
  *(::BandedMatrices.AbstractBandedMatrix, ::BlockBandedMatrices.AbstractBlockBandedMatrix, ::Vararg{Any,N} where N)