function A = toMatrix(bm)
    if ~blockmatrix.isBlockmatrix(bm)
        error('blockmatrix:toMatrix:NotABlockmatrix', 'Input is not a blockmatrix');
    end

    div = blockmatrix.getDivision(bm);
    n = div{1};
    m = div{2};

    N = sum(n);
    M = sum(m);

    A = sparse(N,M);

    n_ind = [0 cumsum(n)];
    m_ind = [0 cumsum(m)];

    for i = 1:size(bm,1)
        for j = 1:size(bm,2)
            if isempty(bm{i,j})
                continue
            end
            % TODO: If this ever fails for large matrices. Try cell2mat instead.
            A(n_ind(i)+1:n_ind(i+1),m_ind(j)+1:m_ind(j+1)) = bm{i,j};
        end
    end
end