# std::cosh(std::complex)

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< cpp‎ | numeric‎ | complex

Defined in header `<complex>` |  |
template< class T > complex<T> cosh( const complex<T>& z ); |  | (since C++11)

Computes complex hyperbolic cosine of a complex value `z`.

### Parameters

z | - | complex value

### Return value

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

### Error handling and special values

Errors are reported consistent with math_errhandling

If the implementation supports IEEE floating-point arithmetic,

- std::cosh ( std::conj (z)) == std::conj ( std::cosh (z))
- std::cosh (z) == std::cosh (-z)
- If `z` is `(+0,+0)`, the result is `(1,+0)`
- If `z` is `(+0,+∞)`, the result is `(NaN,±0)` (the sign of the imaginary part is unspecified) and FE_INVALID is raised
- If `z` is `(+0,NaN)`, the result is `(NaN,±0)` (the sign of the imaginary part is unspecified)
- If `z` is `(x,+∞)` (for any finite non-zero x), the result is `(NaN,NaN)` and FE_INVALID is raised
- If `z` is `(x,NaN)` (for any finite non-zero x), the result is `(NaN,NaN)` and FE_INVALID may be raised
- If `z` is `(+∞,+0)`, the result is `(+∞,+0)`
- If `z` is `(+∞,y)` (for any finite non-zero y), the result is `+∞cis(y)`
- If `z` is `(+∞,+∞)`, the result is `(±∞,NaN)` (the sign of the real part is unspecified) and FE_INVALID is raised
- If `z` is `(+∞,NaN)`, the result is `(+∞,NaN)`
- If `z` is `(NaN,+0)`, the result is `(NaN,±0)` (the sign of the imaginary part is unspecified)
- If `z` is `(NaN,+y)` (for any finite non-zero y), the result is `(NaN,NaN)` and FE_INVALID may be raised
- If `z` is `(NaN,NaN)`, the result is `(NaN,NaN)`

where cis(y) is cos(y) + i sin(y)

### Notes

Mathematical definition of hyperbolic cosine is cosh z =

ez +e-z
2

Hyperbolic cosine is an entire function in the complex plane and has no branch cuts. It is periodic with respect to the imaginary component, with period 2πi

### Examples

Run this code

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

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

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

Output:

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

### See also

sinh(std::complex) | computes hyperbolic sine of a complex number (sh(z)) (function template)
tanh(std::complex) | computes hyperbolic tangent of a complex number (function template)
acosh(std::complex) (C++11) | computes area hyperbolic cosine of a complex number (function template)
coshcoshfcoshl (C++11)(C++11) | computes hyperbolic cosine (ch(x)) (function)
cosh(std::valarray) | applies the function std::cosh to each element of valarray (function template)

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