atan

(PHP 4, PHP 5, PHP 7, PHP 8)

atan —Arc tangent

Description

atan(float$num):float

Returns the arc tangent ofnum in radians.atan() is the inverse function oftan(), which means that$num == tan(atan($num)) for every value ofnum that is in the domain ofatan().

Parameters

num: The argument to process

Return Values

The arc tangent ofnum in radians.

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User Contributed Notes1 note

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Anonymous ¶

10 years ago

Contrary to the current description, it should hold y == tan(atan(y)) for ALL  y.
However, x == atan(tan(x)) only holds for those x which are in the range of atan, which are those x with -pi/2 < x < pi/2.

Of course, those equalities are limited by precision. On my machine
tan(atan(1000)) returns 1000.0000000001.
atan(tan(0)) returns 0 (correct).
atan(tan(M_PI)) returns -1.2246467991474E-16 instead of 0.