mandel_coef.rb

def sum_diagonals(m)
  next_i = 1
  r = [m[0][0]]
  until next_i == m[0].size
    i = next_i
    j = 0
    r[next_i] = 0
    until i < 0
      r[next_i] += m[i][j]
      i -= 1
      j += 1
    end
    next_i += 1
  end
  next_i -= 1
  next_j = 1
  until next_j == m[0].size-1
    i = next_i
    j = next_j
    r[next_i+next_j] = 0
    until i < 1 || j >= m[0].size
      r[next_i+next_j] += m[i][j]
      i -= 1
      j += 1
    end
    next_j += 1
  end
  r << 1 << 1
end

a = [1.0,1.0]
a = sum_diagonals(a.product(a).map {|p| p.reduce(:*)}.each_slice(a.size).to_a)