NAME

std::atan,std::atanf,std::atanl - std::atan,std::atanf,std::atanl

Synopsis

Defined in header <cmath>
float atan ( float arg );
float atanf( float arg ); (since C++11)
double atan ( double arg ); (1) (2)
long double atan ( long double arg );
long double atanl( long double arg ); (3) (since C++11)
double atan ( IntegralType arg ); (4) (since C++11)

1-3) Computes the principal value of the arc tangent of arg
4) A set of overloads or a function template accepting an argument of any integral
type. Equivalent to 2) (the argument is cast to double).

Parameters

arg - value of a floating-point or Integral type

Return value

If no errors occur, the arc tangent of arg (arctan(arg)) in the range [-

π
2

, +

π
2

] radians, is returned.

If a range error occurs due to underflow, the correct result (after rounding) is
returned.

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

* If the argument is ±0, it is returned unmodified
* If the argument is +∞, +π/2 is returned
* If the argument is -∞, -π/2 is returned
* if the argument is NaN, NaN is returned

Notes

POSIX specifies that in case of underflow, arg is returned unmodified, and if that
is not supported, an implementation-defined value no greater than DBL_MIN, FLT_MIN,
and LDBL_MIN is returned.

Examples

// Run this code

#include <iostream>
#include <cmath>

int main()
{
std::cout << "atan(1) = " << atan(1) << " 4*atan(1) = " << 4*atan(1) << '\n';
// special values
std::cout << "atan(Inf) = " << atan(INFINITY)
<< " 2*atan(Inf) = " << 2*atan(INFINITY) << '\n'
<< "atan(-0.0) = " << atan(-0.0) << '\n'
<< "atan(+0.0) = " << atan(0) << '\n';
}

Output:

atan(1) = 0.785398 4*atan(1) = 3.14159
atan(Inf) = 1.5708 2*atan(Inf) = 3.14159
atan(-0.0) = -0
atan(+0.0) = 0

See also

asin
asinf computes arc sine (\({\small\arcsin{x} }\)arcsin(x))
asinl (function)
(C++11)
(C++11)
acos
acosf computes arc cosine (\({\small\arccos{x} }\)arccos(x))
acosl (function)
(C++11)
(C++11)
atan2
atan2f arc tangent, using signs to determine quadrants
atan2l (function)
(C++11)
(C++11)
tan
tanf computes tangent (\({\small\tan{x} }\)tan(x))
tanl (function)
(C++11)
(C++11)
atan(std::complex) computes arc tangent of a complex number (\({\small\arctan{z}
(C++11) }\)arctan(z))
(function template)
atan(std::valarray) applies the function std::atan to each element of valarray
(function template)