amath  1.8.5
Simple command line calculator
asech.c
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1 /*-
2  * Copyright (c) 2014-2018 Carsten Sonne Larsen <cs@innolan.net>
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29 
30 /**
31  * @file asech.c
32  * @brief Inverse hyperbolic secant function
33  */
34 
35 #include "prim.h"
36 
37 /**
38  * @brief Inverse hyperbolic secant function
39  * @details
40  * <pre>
41  * Method
42  * 1+sqrt(1-x*x)
43  * asech(x) = ln( --------------- )
44  * x
45  * when x <= 0
46  * asech(x) = NaN
47  *
48  * when x > 1
49  * asech(x) = NaN
50  * </pre>
51  */
52 double asech(double x)
53 {
54  double a, b, c, d, e, f;
55 
56  if (TRIG_INEXACT(x) || x < 0.0 || x > 1.0)
57  {
58  return NAN;
59  }
60 
61  a = x * x;
62  b = 1.0 - a;
63  c = sqrt(b);
64  d = 1.0 + c;
65  e = d / x;
66  f = log(e);
67  return f;
68 }
double log(double x)
Natural logarithm function (base e)
Definition: log.c:109
double sqrt(double x)
Square root function.
Definition: sqrt.c:119
double asech(double x)
Inverse hyperbolic secant function.
Definition: asech.c:52
#define TRIG_INEXACT(x)
Definition: prim.h:48
#define NAN
Definition: mathr.h:53