n.反正切
Expression to compute the arctangent of (float). 要计算反正切的表达式(浮点小数型)。
Computes the arctangent (in radians) of the specified argument. 计算指定参数的反正切(按弧度)。
The atan() function returns the arctangent of a number as a numeric value between -PI/2 and PI/2 radians. 函数的作用是:返回一个指定数值参数的反正切值。
The method sets up a mapping table which directly relates to the dynamic display range and has only 256 entries using an inverse mapping method instead of calculating the arctangent value directly. 该方法并不直接计算反正切值,而是采取反向映射的办法,建立一个直接和显示动态范围有关、长度仅为256的映射表。