Returns the arc tangent of the argument.
math:atan( $arg as xs:double?xs:double?If $arg is the empty sequence, the function returns the empty sequence.
Otherwise the result is the arc tangent of $arg, as defined
in the specification of the
atan function applied to 64-bit binary floating point values.
The result is in the range -π/2
to +π/2 radians.
The expression math:atan(()) returns ().
The expression math:atan(0) returns 0.0e0.
The expression math:atan(-0.0e0) returns -0.0e0.
The expression math:atan(1.0e0) returns 0.7853981633974483e0.
The expression math:atan(-1.0e0) returns -0.7853981633974483e0.
The expression math:atan(xs:double('NaN')) returns xs:double('NaN').
The expression math:atan(xs:double('INF')) returns 1.5707963267948966e0.
The expression math:atan(xs:double('-INF')) returns -1.5707963267948966e0.
The treatment of the underflow exception is defined in .
If $arg is positive or negative zero, the result is $arg.
If $arg is NaN then the result is NaN.
In other cases the result is an xs:double value representing an angle
θ in radians in the range -π
/2 <=
θ
<= +
π
/2.
