いくつかの補間法

interpolations.rb

#!/usr/bin/env ruby
# interpolations.rb interpolates a data set.
# Gist: https://gist.github.com/t-nissie/9f7cd7d4991530a3fac7
# Author: Takeshi Nishimatsu
# Copying:
#    Copyright (c) 2016 by Takeshi Nishimatsu
#    interpolations.rb is distributed in the hope that
#    it will be useful, but WITHOUT ANY WARRANTY.
#    You can copy, modify and redistribute interpolations.rb,
#    but only under the conditions described in
#    the GNU General Public License version 3 (the "GPLv3").
##
class DataSet
  def initialize(fd, using_x=0, using_y=1)
    @x = []
    @y = []
    while line=fd.gets
      ary = line.strip.split(nil)
      @x << ary[using_x].to_f
      @y << ary[using_y].to_f
    end
  end

  def linear_interpolation(x)
    i=0
    while @x[i]<x
      i+=1
    end
    @y[i-1] + (@y[i] - @y[i-1]) * (x - @x[i-1]) / (@x[i] - @x[i-1])
  end
end

if $0 == __FILE__
  d = DataSet.new(open(ARGV[0], "r"))
  p d.linear_interpolation(ARGV[1].to_f)
  d = DataSet.new(open(ARGV[0], "r"),0,2)
  p d.linear_interpolation(ARGV[1].to_f)
end
#Local variables:
#  compile-command: "ruby dislocation.rb"
#End:

test.dat

1 1 3
2 2 3
3 2 4