Class: Korba::KeplersEquation

Inherits:
Object
  • Object
show all
Includes:
OrbitUtils
Defined in:
lib/korba/keplers_equation.rb

Constant Summary collapse

MAX_ITERATIONS = 
1000

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from OrbitUtils

#deg_to_rad, #distance, #eccentric_anomaly, #height_at_apogee, #height_at_perigee, #normalize_deg, #normalize_rad, #path_angle, #rad_to_deg, #semi_major_axis, #true_anomaly, #velocity

Constructor Details

#initialize(eccentricity:, mean_anomaly:) ⇒ KeplersEquation

Returns a new instance of KeplersEquation.



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# File 'lib/korba/keplers_equation.rb', line 9

def initialize(eccentricity:, mean_anomaly:)
  super()
  @eccentricity = eccentricity
  @mean_anomaly = mean_anomaly
end

Instance Attribute Details

#eccentricity ⇒ Object (readonly)

Returns the value of attribute eccentricity.



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# File 'lib/korba/keplers_equation.rb', line 7

def eccentricity
  @eccentricity
end

#mean_anomaly ⇒ Object (readonly)

Returns the value of attribute mean_anomaly.



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# File 'lib/korba/keplers_equation.rb', line 7

def mean_anomaly
  @mean_anomaly
end

Instance Method Details

#solve(tolerance = 1e-10) ⇒ Object 



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# File 'lib/korba/keplers_equation.rb', line 16

def solve(tolerance = 1e-10)
  m_rad = deg_to_rad(mean_anomaly)

  if eccentricity < 0.8
    en = m_rad
  else
    en = Math::PI
  end

  MAX_ITERATIONS.times do
    # f(E) = E - e*sin(E) - M
    # f'(E) = 1 - e*cos(E)

    sin_en = Math.sin(en.to_f)
    cos_en = Math.cos(en.to_f)

    f = en - eccentricity * sin_en - m_rad
    f_dot = 1 - eccentricity * cos_en

    # 更新
    delta = f / f_dot
    en = en - delta

    # 収束判定
    break if delta.abs < tolerance
  end

  en
end