X = (A + B) / 2
X = A * {1 - [1 - cos(X * pi)] / 2} + B * [1 - cos(X * pi)] / 2
X = [(B‘ - B) - (A‘ - A)] * X^3 + {(A‘ - A) - [(B‘ - B) - (A‘ - A)]} * X^2 + (B - A‘) * X + A
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几种常见的插值法
原文：http://www.cnblogs.com/betairy-linkzeldagg/p/3775572.html
