exs.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
 * are met:
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 */

/**
 * @file  exs.c
 * @brief Exsecant function
 */

#include "prim.h"

/**
 * @brief   Exsecant function
 * @details
 * <pre>
 * exsec(x) = sec(x)-1
 *          = (1-cos(x))/cos(x)
 *          = ver(x)/cos(x)
 *          = ver(x)*sec(x)
 *          = 2*sin(x/2)*sin(x/2)*sec(x)
 * </pre>
 */
double exs(double x)
{
    return ver(x) * sec(x);
}