The weights calculated with the UK system always have some negative values which make the estimation impractical, and so in many cases, the weights with nonnegative values are required.

• 然而，用泛克立格方程组计算估计权值时由于未对权的符号作任何限制，从而使得计算出的权值经常出现负权现象，而负权的存在有许多弊端，所以在许多应用中有必要对权值作非负要求。