# atan

(PHP 4, PHP 5, PHP 7)

atan역탄젠트

### 설명

float atan ( float `\$arg` )

`arg` 라디안의 역탄젠트 값을 반환합니다. atan()tan()의 역함수로, atan()의 범위 안에 있는 모든 값에 대하여 a==tan(atan(a))가 성립합니다.

`arg`

계산할 인수

### 반환값

`arg` 라디안의 역탄젠트.

### User Contributed Notes 4 notes

12
Anonymous
7 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 machinetan(atan(1000)) returns 1000.0000000001.atan(tan(0)) returns 0 (correct).atan(tan(M_PI)) returns -1.2246467991474E-16 instead of 0. ```
darren_wheatley at hotmail dot com
18 years ago
``` Arc Tan curve manipulation.I used this formula to help with increasing and then diminishing return for y given an increasing x for a game.Ie: Food production (output) is y. Food research is x.The more research you put into x the more you produce, however after a certain point you get less reward. y = atan(x - pi()) + pi()/2;The + pi()/2 moves it up the y axis so you'd add more if you want it to start higher.The x - pi() moves it to the right so you'd minus more to move it more.If you want stretched along the y axis change it to 2 * atan( ...... )Dunno how useful it is... but it's there.Daz ```
joelperr at kiwi-interactif dot com
16 years ago
``` to obtain the direction of the line, you are better to use the <? atan2((y2-y1)/(x2-x1)) ?> function, since the regular atan function will only return arguments in the half-plane, ie. if y2-y1 and x2-x1 are negative, atan will give you an angle measurement less than 90 degrees, while it really should be  between 180 and 270 ```
-7
Ts.Saltan
6 years ago
``` arcctg functionfunction actg(\$arg){    return acos(\$arg/(sqrt(1 + \$arg * \$arg)));} ```