什么是 log ??

我们知道 10^2 = 100，10^3 = 1000 反过来说，10 的多少次方是100 呢？10的多少次方是1000呢？ 由于 10^2 = 100，因此我们说：log 100 = 2 简单来说，log 就是「次方」的相反，正如加是减的相反一样。 log 其中一个用处就是把很大的数字 "scale down"，用一个小的数字来代表，方便描述或使用。 例如地震的强度与地壳震动所产生的能量有关，但这些能量的大小往往是10的 8 - 9 次方，在日常生活中，我们很难用那么大的数字去把这个强度告诉其他人：「这个地震的强度是 10 的 8 次方…」因此便有「黎克特制」的出现，就是利用 log 把这些数字「缩小」，让人易于描述。
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 plex 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:个logb(x)的b系个底数
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参考: en. *** /wiki/Logarithm