The mathLib.atan2() system function computes the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value.
mathLib.atan2( y FLOAT in, x FLOAT in) returns (result FLOAT)
x INT = 5; y INT = 1; result FLOAT = mathLib.atan2(y, x); // result is 0.19739555984988078