ATAN2(real-y, real-x)

Returns the arc tangent of y ÷ x, using the signs of both arguments to determine the correct quadrant of the angle. The result is given in radians, in the range -PI# to PI#.

Examples

PRINT ATAN2(1, 1)

Produces approximately 0.785398 (π/4).

PRINT ATAN2(1, -1)

Produces approximately 2.356194 (3π/4).

PRINT ATAN2(-1, -1)

Produces approximately -2.356194 (-3π/4).

PRINT ATAN2(-1, 1)

Produces approximately -0.785398 (-π/4).

REM Compute angle of a vector
dx# = 3
dy# = 4
angle# = ATAN2(dy#, dx#)
PRINT "Angle = "; angle#; " radians"

Notes

Unlike ATAN, which only returns results in -π/2 … π/2, ATAN2 resolves the full circle by considering both x and y signs.
Input range: both arguments may be any real numbers.
Return range: -π ≤ result ≤ π radians.
To convert to degrees, multiply by 180 / PI.

See also: ATAN · SIN · COS · TAN