/*							cosh.c
 *
 *	Hyperbolic cosine
 *
 *
 *
 * SYNOPSIS:
 *
 * double x, y, cosh();
 *
 * y = cosh( x );
 *
 *
 *
 * DESCRIPTION:
 *
 * Returns hyperbolic cosine of argument in the range MINLOG to
 * MAXLOG.
 *
 * cosh(x)  =  ( exp(x) + exp(-x) )/2.
 *
 *
 *
 * ACCURACY:
 *
 *                      Relative error:
 * arithmetic   domain     # trials      peak         rms
 *    DEC       0,2         20000       2.9e-17     8.6e-18
 *    IEEE     +-MAXLOG     30000       2.6e-16     5.7e-17
 *
 *
 * ERROR MESSAGES:
 *
 *   message         condition      value returned
 * cosh overflow    |x| > MAXLOG       MAXNUM
 *
 *
 */

/*							cosh.c */

/*
Cephes Math Library Release 2.0:  April, 1987
Copyright 1985, 1987 by Stephen L. Moshier
Direct inquiries to 30 Frost Street, Cambridge, MA 02140
*/

#include "mconf.h"
extern double MAXLOG, MAXNUM;

double cosh(x)
double x;
{
double y;
double exp(), ldexp();

if( x < 0 )
	x = -x;
if( x > MAXLOG )
	{
	mtherr( "cosh", OVERFLOW );
	return( MAXNUM );
	}	
y = exp(x);
y = y + 1.0/y;
y = ldexp( y, -1 );
return( y );
}