lambdaRank: lambda calculate wrong

[aker218]

    delta = abs(single_dcgs[(i,j)] + single_dcgs[(j,i)] - single_dcgs[(i,i)] -single_dcgs[(j,j)])/IDCG

for this line，you mean the ith document in true_scores should be position i ? after checking the data, it seems wrong, maybe we should sort true socres and save the position of documents in true score which can be used here.