sech.c

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/*-
 * Copyright (c) 2014-2018 Carsten Sonne Larsen <cs@innolan.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
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/**
 * @file  sech.c
 * @brief Hyperbolic secant function
 */

#include "prim.h"

/**
 * @brief   Hyperbolic secant function
 * @details
 * <pre>
 * sech(x) = 1/cosh(x)
 * </pre>
 */
double sech(double x)
{
    double a = cosh(x);
    if (TRIG_INEXACT(a))
    {
        return NAN;
    }
    return 1.0 / a;
}