ELO implementation for PicAFight

gistfile1.rb

# ELO implementation for PicAFight
# using ELO formula from http://en.wikipedia.org/wiki/Elo_rating_system#Mathematical_details and a K value of 32
# all contestants start with ELO rating of 1500

    ra = pic1.elo
    rb = pic2.elo
    
    qa = 10**((ra + 0.0)/400.0) + 0.0
    qb = 10**((rb + 0.0)/400.0) + 0.0

    ea = qa / (qa + qb)
    eb = qb / (qa + qb)

    # a win is worth 1 point, a loss is worth 0 points
    sa = 1 - (params[:win]).to_i
    sb = params[:win].to_i

    ka = 32
    kb = 32

    radelta = ka * (sa - ea)
    rbdelta = kb * (sb - eb)

    ra = ra + radelta
    rb = rb + rbdelta
    
    # store new ELO value back
    pic1.elo = ra.to_i
    pic2.elo = rb.to_i