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    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() は tan() の逆関数です。 つまり、atan() の定義域にある num の全ての値に対して、$num == tan(atan($num)) が成立します。

    パラメータ

    num

    処理する引数。

    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）

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    User Contributed Notes 3 notes

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    11
    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.
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    1
    darren_wheatley at hotmail dot com
    21 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
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    0
    joelperr at kiwi-interactif dot com
    18 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
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