minkowski distance


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by Yonaba

in lua

Source Code

-- Minkowski Distance distance implementation
-- See: http://en.wikipedia.org/wiki/Minkowski_distance

-- Returns the Minkowski distance between two vectors
-- p       : a first vector
-- q       : a second vector
-- n       : the distance order
-- returns : the distance between p and q
local function minkowski_distance(p, q, n)
  assert(#p == #q, 'vectors must have the same length')
  local s = 0
  for i in ipairs(p) do
    s = s + math.abs(p[i] - q[i]) ^ n
  end
  return s ^ (1 / n)
end

return minkowski_distance
-- Tests for minkowski_distance.lua
local mdist = require 'minkowski_distance'

local total, pass = 0, 0

local function dec(str, len)
  return #str < len
     and str .. (('.'):rep(len-#str))
      or str:sub(1,len)
end

local function run(message, f)
  total = total + 1
  local ok, err = pcall(f)
  if ok then pass = pass + 1 end
  local status = ok and 'PASSED' or 'FAILED'
  print(('%02d. %68s: %s'):format(total, dec(message,68), status))
end

-- Fuzzy equality test
local function fuzzyEqual(a, b)
  return math.abs(a-b) < 1e-8
end

run('Minkowski distance test', function()
  assert(mdist({},{}, 1), 0)
  assert(mdist({1,2,3},{4,5,6}, 1), 9)
  assert(fuzzyEqual(mdist({1,2,3},{4,5,6},2), 27^(1/2)))
  assert(not pcall(mdist,{1,2,3},{4,5}))
end)

print(('-'):rep(80))
print(('Total : %02d: Pass: %02d - Failed : %02d - Success: %.2f %%')
  :format(total, pass, total-pass, (pass*100/total)))