Available in all subroutines.

Computes the principal value of the arc tangent of its argument x.


x - Floating point value.

Return Value

Upon successful completion, this function returns the arc tangent of x in the range -math.PI_2 to math.PI_2 radians inclusive.

If x is math.NAN, a NaN will be returned.

If x is ±0, x will be returned.

If x is math.POS_INFINITY or math.NEG_INFINITY, ±math.PI_2 will be returned.

If x is subnormal, a range error occurs and x will be returned.


If the x argument is subnormal, then fastly.error will be set to ERANGE.


declare local FLOAT;
set = math.atan(1);