atan

(PHP 4, PHP 5)

atan — 反正切

说明

float atan ( float $arg )

返回 arg 的反正切值，单位是弧度。atan() 是 tan() 的反函数，它的意思是在 atan() 范围里的每个值都是 a==tan(atan(a))。

参见: atanh()、 asin() 和 acos()。

PHP手册 - N: 反正切

用户评论:

joelperr at kiwi-interactif dot com (12-Jan-2006 01:12)

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

darren_wheatley at hotmail dot com (28-Nov-2003 02:24)

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

jmartin at columbiaservices dot net (21-Nov-2003 08:10)

I looked for hours trying to come up with a formula to solve the direction that a line was heading (in degrees) when x1,y1 were the starting points, and x2,y2 are the ending points. Here is the equasion I was given, I hope this helps anyone in need of the same one. $angle = rad2deg(atan2(($y2 - $y1), ($x2 - x1)));