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Source file src/math/sinh.go

Documentation: math

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package math
  
  /*
  	Floating-point hyperbolic sine and cosine.
  
  	The exponential func is called for arguments
  	greater in magnitude than 0.5.
  
  	A series is used for arguments smaller in magnitude than 0.5.
  
  	Cosh(x) is computed from the exponential func for
  	all arguments.
  */
  
  // Sinh returns the hyperbolic sine of x.
  //
  // Special cases are:
  //	Sinh(±0) = ±0
  //	Sinh(±Inf) = ±Inf
  //	Sinh(NaN) = NaN
  func Sinh(x float64) float64
  
  func sinh(x float64) float64 {
  	// The coefficients are #2029 from Hart & Cheney. (20.36D)
  	const (
  		P0 = -0.6307673640497716991184787251e+6
  		P1 = -0.8991272022039509355398013511e+5
  		P2 = -0.2894211355989563807284660366e+4
  		P3 = -0.2630563213397497062819489e+2
  		Q0 = -0.6307673640497716991212077277e+6
  		Q1 = 0.1521517378790019070696485176e+5
  		Q2 = -0.173678953558233699533450911e+3
  	)
  
  	sign := false
  	if x < 0 {
  		x = -x
  		sign = true
  	}
  
  	var temp float64
  	switch true {
  	case x > 21:
  		temp = Exp(x) / 2
  
  	case x > 0.5:
  		temp = (Exp(x) - Exp(-x)) / 2
  
  	default:
  		sq := x * x
  		temp = (((P3*sq+P2)*sq+P1)*sq + P0) * x
  		temp = temp / (((sq+Q2)*sq+Q1)*sq + Q0)
  	}
  
  	if sign {
  		temp = -temp
  	}
  	return temp
  }
  
  // Cosh returns the hyperbolic cosine of x.
  //
  // Special cases are:
  //	Cosh(±0) = 1
  //	Cosh(±Inf) = +Inf
  //	Cosh(NaN) = NaN
  func Cosh(x float64) float64
  
  func cosh(x float64) float64 {
  	if x < 0 {
  		x = -x
  	}
  	if x > 21 {
  		return Exp(x) / 2
  	}
  	return (Exp(x) + Exp(-x)) / 2
  }
  

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