PHP Functions Essential Reference

atan2

float atan2(float x, float y) 

Returns the arctangent based on an XY coordinate.

Returns:

Arctangent as a float

Description:

This function returns the value of the arctangent of the point denoted by the x and y parameters. The return value is in radians, in the range -pi to pi (approximately -3.14 to 3.14).

Version:

PHP 3 since 3.0.5, PHP 4

See also:

acos() 
asin() 
atan() 
cos() 
sin() 
tan() 

Example:

Calculate the arctangent of a coordinate

$tanx = -1; $tany = 1; echo "The arctangent of $tanx/$tany is ", atan2($tanx, $tany);