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std::atan

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

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 [-

; +

] 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, and implementation-defined value no greater than DBL_MIN, FLT_MIN, and LDBL_MIN is returned.

Examples

#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

asin	computes arc sine (arcsin(x)) (function)
acos	computes arc cosine (arccos(x)) (function)
atan2	arc tangent, using signs to determine quadrants (function)
tan	computes tangent (tan(x)) (function)
atan(std::complex) (C++11)	computes arc tangent of a complex number (arctan(z)) (function template)
atan(std::valarray)	applies the function `std::atan` to each element of valarray (function template)
C documentation for `atan`