[julia-users] Using Cartesian to define multidimensional convolution

[Derek Thomas]

Hi all,

I'm trying to implement a multidimensional convolution defined like this in 
2d:
  
"We initialize to zero a matrix c and add to it, starting at the (i,j)th 
position, submatrices b[i, j] * a[:, :] padded with zeros."

I have this function:
stagedfunction convn{T,N}(A::Array{T,N}, B::Array{T,N})
    quote
        retsize = [size(A)...] + [size(B)...]
        retsize = tuple(retsize...)
        ret = zeros(T, retsize)
        @nloops $N i A begin
            @nloops $N j B begin
                (@nref $N ret k->(i_d + j_d)) = (@nref A i) * (@nref B j)
            end
        end
        return ret
    end
end

but I'm getting a cryptic ERROR: wrong number of arguments message to this 
input

A = randn(5, 5)

convn(A, A)

Any help is appreciated.  Thanks,

Derek