Class: Spliner::Spliner

Inherits:
Object
  • Object
show all
Defined in:
lib/spliner/spliner.rb

Overview

Spliner::Spliner provides cubic spline interpolation based on provided key points on a X-Y curve.

Example

require 'spliner'
# Initialize a spline interpolation with x range 0.0..2.0
my_spline = Spliner::Spliner.new [0.0, 1.0, 2.0], [0.0, 1.0, 0.5]
# Perform interpolation on 31 values ranging from 0..2.0
x_values = (0..30).map {|x| x / 30.0 * 2.0 }
y_values = x_values.map {|x| my_spline[x] }

Algorithm based on en.wikipedia.org/wiki/Spline_interpolation

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(key_points, options) ⇒ Spliner #initialize(x, y, options) ⇒ Spliner

Creates a new Spliner::Spliner object to interpolate between the supplied key points.

The key points shoul be in increaing X order. When duplicate X values are encountered, the spline is split into two or more discontinuous sections.

The extrapolation method may be :linear by default, using a linear extrapolation at the curve ends using the curve derivative at the end points. The :hold method will use the Y value at the nearest end point of the curve.

Overloads:

  • #initialize(key_points, options) ⇒ Spliner

    Parameters:

    • key_points (Hash{Float => Float}) —

      keys are X values in increasing order, values Y

    • options (Hash)

    Options Hash (options):

    • :extrapolate (Range, String) — default: '0%' —

      either a range or percentage, eg ‘10.0%’

    • :emethod (Symbol) — default: :linear —

      extrapolation method

  • #initialize(x, y, options) ⇒ Spliner

    Parameters:

    • x (Array(Float), Vector) —

      the X values of the key points

    • y (Array(Float), Vector) —

      the Y values of the key points

    • options (Hash)

    Options Hash (options):

    • :extrapolate (Range, String) — default: '0%' —

      either a range or percentage, eg ‘10.0%’

    • :emethod (Symbol) — default: :linear —

      extrapolation method



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# File 'lib/spliner/spliner.rb', line 47

def initialize(*param)
  # sort parameters from two alternative initializer signatures
  x, y = nil
  case param.first
  when Array, Vector
    xx,yy, options = param
    x = xx.to_a
    y = yy.to_a
  else
    points, options = param
    x = points.keys
    y = points.values
  end
  options ||= {}

  @sections = split_at_duplicates(x).map {|slice| SplinerSection.new x[slice], y[slice] }

  # Handle extrapolation option parameter
  options[:extrapolate].tap do |ex|
    case ex
    when /^\d+(\.\d+)?\s?%$/
      percentage = ex[/\d+(\.\d+)?/].to_f
      span = x.last - x.first
      extra = span * percentage * 0.01
      @range = (x.first - extra)..(x.last + extra)
    when Range
      @range = ex
    when nil
      @range = x.first..x.last
    else
      raise 'Unable to use extrapolation parameter'
    end
  end
  @extrapolation_method = options[:emethod] || :linear
end

Instance Attribute Details

#range ⇒ Object (readonly)

Returns the value of attribute range.



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# File 'lib/spliner/spliner.rb', line 20

def range
  @range
end

Instance Method Details

#get(v) ⇒ Object Also known as: []

returns an interpolated value



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# File 'lib/spliner/spliner.rb', line 93

def get(v)
  i = @sections.find_index {|section| section.range.member? v }
  if i
    @sections[i].get v
  elsif range.member? v
    extrapolate(v)
  else
    nil
  end
end

#sections ⇒ Object

The number of non-continuous sections used



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# File 'lib/spliner/spliner.rb', line 107

def sections
  @sections.size
end