Function number_diff::atan

pub fn atan(func: Function) -> Function

Creates a Function equal to the arctangent of the passed Function

i.e f(x) ⟹ atan(f(x))

Example:

    let x = function::default();
    let atan_of_x = atan(x);
    assert_eq!(atan_of_x.call(1.), PI/4.);