#!/usr/bin/env ruby

target_file = ARGV.shift
tau = ARGV.shift.to_f
m = ARGV.shift.to_i

tau_m = tau * m

data = []
open(target_file){|src|
	src.each{|line| data << line.to_f}
}

s = 0.0	# s=Y(0)
v = 0.0	# v=Y(m)

(0...m).each{|i|
	s += data[i]
	v += data[i+m]
}

D = []
D << (v-s)/m
(1...(data.size + 1 - 2*m)).each{|i|
	D << D.last + (data[i-1] - 2*data[i+m-1] + data[i+2*m-1])/m
}

s = 0.0
(0...(data.size + 1 - 2*m)).each{|i|
	s += D[i]**2
}
puts "AVAR: #{Math::sqrt(s/(data.size + 1 - 2*m)/2)}"