n.反正切

Expression to compute the arctangent of (float). 要計(jì)算反正切的表達(dá)式（浮點(diǎn)小數(shù)型）。

Computes the arctangent (in radians) of the specified argument. 計(jì)算指定參數(shù)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. 函數(shù)的作用是：返回一個(gè)指定數(shù)值參數(shù)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. 該方法并不直接計(jì)算反正切值,而是采取反向映射的辦法,建立一個(gè)直接和顯示動(dòng)態(tài)范圍有關(guān)、長(zhǎng)度僅為256的映射表。