# std::cos(std::complex)

< cpp‎ | numeric‎ | complex

C++
 Language Standard library headers Concepts Utilities library Strings library Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11) Technical Specifications

Numerics library
 Common mathematical functions Floating-point environment Complex numbers Numeric arrays Pseudo-random number generation Compile-time rational arithmetic (C++11) Generic numeric operations iota (C++11) accumulate inner_product adjacent_difference partial_sum

std::complex
Member functions
Non-member functions
 real imag abs arg norm conj proj (C++11) polar operator""ioperator""ifoperator""il (C++14)(C++14)(C++14)
Exponential functions
Power functions
Trigonometric functions
 sin cos tan
 asin (C++11) acos (C++11) atan (C++11)
Hyperbolic functions
 asinh (C++11) acosh (C++11) atanh (C++11)

 Defined in header `` template< class T > complex cos( const complex& z );

Computes complex cosine of a complex value `z`.

## Contents

### Parameters

 z - complex value

### Return value

If no errors occur, the complex cosine of `z` is returned.

Errors and special cases are handled as if the operation is implemented by `std::cosh(i*z)`, where `i` is the imaginary unit.

### Notes

The cosine is an entire function on the complex plane, and has no branch cuts.

Mathematical definition of the cosine is cos z =
 eiz+e-iz 2

### Example

```#include <iostream>
#include <cmath>
#include <complex>

int main()
{
std::cout << std::fixed;
std::complex<double> z(1, 0); // behaves like real cosine along the real line
std::cout << "cos" << z << " = " << std::cos(z)
<< " ( cos(1) = " << std::cos(1) << ")\n";

std::complex<double> z2(0, 1); // behaves like real cosh along the imaginary line
std::cout << "cos" << z2 << " = " << std::cos(z2)
<< " (cosh(1) = " << std::cosh(1) << ")\n";
}```

Output:

```cos(1.000000,0.000000) = (0.540302,-0.000000) ( cos(1) = 0.540302)
cos(0.000000,1.000000) = (1.543081,-0.000000) (cosh(1) = 1.543081)```