std::atan

 

C++

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Technical Specifications

 

Numerics library

Common mathematical functions

Floating-point environment

Complex numbers

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Compile-time rational arithmetic (C++11)

Generic numeric operations

iota (C++11)

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Common mathematical functions

Functions
Basic operations
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
Exponential functions
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
Power functions
sqrt cbrt (C++11)	hypot (C++11) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Error and gamma functions
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Nearest integer floating point operations
ceil floor roundlroundllround (C++11)(C++11)(C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11)(C++11)(C++11)
Floating point manipulation functions
ldexp scalbnscalbln (C++11)(C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11)(C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

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 [-

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, and 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	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