quadratic 意为「二次的」,为什么其前缀是通常与数字 4 有关的 quad-? - 知乎 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
通过递推公式求通项公式? - 知乎 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