structsym.jl

function isstructsym(A::SparseMatrixCSC)
    m, n = size(A)
    if m != n; return false; end

    colptr = A.colptr
    rowval = A.rowval
    nzval = A.nzval
    tracker = copy(A.colptr)
    @inbounds for col = 1:A.n
        for p = tracker[col]:colptr[col+1]-1
            val = nzval[p]
            row = rowval[p]
            row < col && return false
            if row > col
                row2 = rowval[tracker[row]]
                row2 > col && return false
                if row2 == col
                    tracker[row] += 1
                end
            end
        end
    end
    return true
end