什麼是 log ??

我們知道 10^2 = 100，10^3 = 1000
反過來說，10 的多少次方是100 呢？10的多少次方是1000呢？
由於 10^2 = 100，因此我們說：log 100 = 2
簡單來說，log 就是「次方」的相反，正如加是減的相反一樣。

log 其中一個用處就是把很大的數字 "scale down"，用一個小的數字來代表，方便描述或使用。

例如地震的強度與地殼震動所產生的能量有關，但這些能量的大小往往是10的 8 - 9 次方，在日常生活中，我們很難用那麼大的數字去把這個強度告訴其他人：「這個地震的強度是 10 的 8 次方…」因此便有「黎克特制」的出現，就是利用 log 把這些數字「縮小」，讓人易於描述。

In mathematics, a logarithm (to base b) of a number x is the exponent y of the power by such that x = by. The value used for the base b must be neither 0 nor 1 (nor a root of 1 in the case of the extension to complex numbers), and is typically 10, e, or 2. The base-b logarithm is usually written as
[logb(x)]

When x and b are further restricted to positive real numbers, the logarithm is a unique real number.


The function [logb(x)] depends on both b and x, but the term logarithm function (or logarithmic function) in standard usage refers to a function of the form logb(x) in which the base b is fixed and so the only argument is x. Thus there is one logarithm function for each value of the base b (which must be positive and must differ from 1). Viewed in this way, the base-b logarithm function is the inverse function of the exponential function bx. The word "logarithm" is often used to refer to a logarithm function itself as well as to particular values of this function.

注意:個logb(x)的b係個底數,電腦有問題