PHP : Function Reference : Mathematical Functions : atan
joelperr
to obtain the direction of the line, you are better to use the <? atan2((y2y1)/(x2x1)) ?> function, since the regular atan function will only return arguments in the halfplane, ie. if y2y1 and x2x1 are negative, atan will give you an angle measurement less than 90 degrees, while it really should be between 180 and 270
jmartin
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)));
darren_wheatley
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
