##### Synopsis

    #include <math.h>
    double cosh(double x);

##### Description

cosh calculates the hyperbolic cosine of x.

##### Fast math library behavior

If |x| >~ 709.782, errno is set to EDOM and cosh returns HUGE_VAL.

##### IEC 60559 math library behavior

If x is +?, -?, or NaN, cosh returns |x|.
If |x| >~ 709.782, cosh returns +? or -? depending upon the sign of x.

##### Portability

cosh conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).