quadratic: 1.来自 Wikipedia： In mathematics, the term quadratic describes something that pertains to squares (平方/二次幂), to the operation (运算)of squaring, to terms of the second degree (次/幂), or equations or formulas that involve such terms. Quadratus is Latin for square. 2.来自iCIBA: an equation in which the highest power (幂，乘方) of an unknown quantity is a square ...
形如 x n + 1 = a 2 x n 2 + a 1 x n + a 0 的递推公式被称为 quadratic map, 它是 quadratic recurrence equation 的特例 (quadratic map 是没有交叉项的 quadratic recurrence equation) . 一些 quadratic map 存在通项公式 (即存在 x n 的解析解), 但大部分是不存在的.
