PHP 7.2.7 Released

# atan

(PHP 4, PHP 5, PHP 7)

atanArc tangente

### Description

float atan ( float \$arg )

Retourne l'arc tangent de arg, en radians. atan() est la fonction inverse de tan(), ce qui signifie que a==tan(atan(a)) pour toute valeur qui soit dans l'intervalle de validité de atan().

### Liste de paramètres

arg

L'argument à traiter

### Valeurs de retour

L'arc tangent de arg, en radians.

### User Contributed Notes 4 notes

Anonymous
3 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.
darren_wheatley at hotmail dot com
14 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
12 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
Ts.Saltan
2 years ago
arcctg function

function actg(\$arg){
return acos(\$arg/(sqrt(1 + \$arg * \$arg)));
}