# atan

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

atan逆正接（アークタンジェント）

### 説明

atan(float `\$num`): float

`num` のアークタンジェントをラジアンで返します。 atan() is the は tan() の逆関数で、 atan() がとりうる範囲内のすべての `num` について `\$num == tan(atan(\$num))` が成立します。

`num`

### 戻り値

`num` のアークタンジェントをラジアンで返します。

### 参考

• tan() - 正接（タンジェント）
• atanh() - 逆双曲線正接（アークハイパボリックタンジェント）
• asin() - 逆正弦（アークサイン）
• acos() - 逆余弦（アークコサイン）

### User Contributed Notes 4 notes

11
Anonymous
9 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
19 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
17 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`
-8
Ts.Saltan
7 years ago
`arcctg functionfunction actg(\$arg){ return acos(\$arg/(sqrt(1 + \$arg * \$arg)));}` 