Atan2

In a variety of computer languages, the function atan2 is the arctangent function with two arguments. For any real number (e.g., floating point) arguments x and y not both equal to zero, atan2(y, x) is the angle in radians between the positive x-axis of a plane and the point given by the coordinates (x, y) on it. The angle is positive for counter-clockwise angles (upper half-plane, y > 0), and negative for clockwise angles (lower half-plane, y < 0).

The purpose of using two arguments instead of one, i.e. just computing a atan(y/x), is to gather information on the signs of the inputs in order to return the appropriate quadrant of the computed angle, which is not possible for the single-argument arctangent function. It also avoids the problem of division by zero, as atan2(y, 0) will return a valid answer as long as y is non-zero.

The atan2 function was first introduced in computer programming languages, but now it is also common in other fields of science and engineering. It dates back at least as far as the FORTRAN programming language and is currently found in many modern programming languages. Among these languages are: C's math.h standard library, the Java Math library, .NET's System.Math (usable from C#, VB.NET, etc.), the Python math module, the Ruby Math module, and elsewhere. In addition, many scripting languages, such as Perl, include the C-style atan2(y,x) function.

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