fixed cpplint issues and updated docs (#2830)

docs/Advanced-Topics.rst

@@ -39,7 +39,7 @@ LambdaRank
 
 -  Use ``label_gain`` to set the gain(weight) of ``int`` label.
 
--  Use ``max_position`` to set the NDCG optimization position.
+-  Use ``lambdarank_truncation_level`` to truncate the max DCG.
 
 Cost Efficient Gradient Boosting
 --------------------------------

docs/Parameters.rst

@@ -99,9 +99,9 @@ Core Parameters
 
       -  ``lambdarank``, `lambdarank <https://papers.nips.cc/paper/2971-learning-to-rank-with-nonsmooth-cost-functions.pdf>`__ objective. `label_gain <#label_gain>`__ can be used to set the gain (weight) of ``int`` label and all values in ``label`` must be smaller than number of elements in ``label_gain``
 
-      -  ``rank_xendcg``, `XE_NDCG_MART <https://arxiv.org/abs/1911.09798>`__ ranking objective function. aliases: ``xendcg``, ``xe_ndcg``, ``xe_ndcg_mart``, ``xendcg_mart``.
+      -  ``rank_xendcg``, `XE_NDCG_MART <https://arxiv.org/abs/1911.09798>`__ ranking objective function, aliases: ``xendcg``, ``xe_ndcg``, ``xe_ndcg_mart``, ``xendcg_mart``
 
-      -  ``rank_xendcg`` is faster than ``lambdarank`` and achieves the similar performance as ``lambdarank``
+      -  ``rank_xendcg`` is faster than and achieves the similar performance as ``lambdarank``
 
       -  label should be ``int`` type, and larger number represents the higher relevance (e.g. 0:bad, 1:fair, 2:good, 3:perfect)
 
@@ -805,9 +805,9 @@ Objective Parameters
 
 -  ``objective_seed`` :raw-html:`<a id="objective_seed" title="Permalink to this parameter" href="#objective_seed">&#x1F517;&#xFE0E;</a>`, default = ``5``, type = int
 
-   -  random seed for objectives, if random process is needed
+   -  used only in ``rank_xendcg`` objective
 
-   -  used in ``rank_xendcg``
+   -  random seed for objectives, if random process is needed
 
 -  ``num_class`` :raw-html:`<a id="num_class" title="Permalink to this parameter" href="#num_class">&#x1F517;&#xFE0E;</a>`, default = ``1``, type = int, aliases: ``num_classes``, constraints: ``num_class > 0``
 
@@ -885,7 +885,7 @@ Objective Parameters
 
    -  used only in ``lambdarank`` application
 
-   -  used for truncating the max_ndcg, refer to "truncation level" in the Sec.3 of `LambdaMART paper <https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/MSR-TR-2010-82.pdf>`__ .
+   -  used for truncating the max DCG, refer to "truncation level" in the Sec. 3 of `LambdaMART paper <https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/MSR-TR-2010-82.pdf>`__
 
 -  ``lambdarank_norm`` :raw-html:`<a id="lambdarank_norm" title="Permalink to this parameter" href="#lambdarank_norm">&#x1F517;&#xFE0E;</a>`, default = ``true``, type = bool
 

include/LightGBM/config.h

@@ -128,8 +128,8 @@ struct Config {
   // descl2 = label is anything in interval [0, 1]
   // desc = ranking application
   // descl2 = ``lambdarank``, `lambdarank <https://papers.nips.cc/paper/2971-learning-to-rank-with-nonsmooth-cost-functions.pdf>`__ objective. `label_gain <#label_gain>`__ can be used to set the gain (weight) of ``int`` label and all values in ``label`` must be smaller than number of elements in ``label_gain``
-  // descl2 = ``rank_xendcg``, `XE_NDCG_MART <https://arxiv.org/abs/1911.09798>`__ ranking objective function. aliases: ``xendcg``, ``xe_ndcg``, ``xe_ndcg_mart``, ``xendcg_mart``.
-  // descl2 = ``rank_xendcg`` is faster than ``lambdarank`` and achieves the similar performance as ``lambdarank``
+  // descl2 = ``rank_xendcg``, `XE_NDCG_MART <https://arxiv.org/abs/1911.09798>`__ ranking objective function, aliases: ``xendcg``, ``xe_ndcg``, ``xe_ndcg_mart``, ``xendcg_mart``
+  // descl2 = ``rank_xendcg`` is faster than and achieves the similar performance as ``lambdarank``
   // descl2 = label should be ``int`` type, and larger number represents the higher relevance (e.g. 0:bad, 1:fair, 2:good, 3:perfect)
   std::string objective = "regression";
 
@@ -706,8 +706,8 @@ struct Config {
 
   #pragma region Objective Parameters
 
+  // desc = used only in ``rank_xendcg`` objective
   // desc = random seed for objectives, if random process is needed
-  // desc = used in ``rank_xendcg``
   int objective_seed = 5;
 
   // check = >0
@@ -768,7 +768,7 @@ struct Config {
 
   // check = >0
   // desc = used only in ``lambdarank`` application
-  // desc = used for truncating the max_ndcg, refer to "truncation level" in the Sec.3 of `LambdaMART paper <https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/MSR-TR-2010-82.pdf>`__ .
+  // desc = used for truncating the max DCG, refer to "truncation level" in the Sec. 3 of `LambdaMART paper <https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/MSR-TR-2010-82.pdf>`__
   int lambdarank_truncation_level = 20;
 
   // desc = used only in ``lambdarank`` application

src/objective/rank_objective.hpp

@@ -69,7 +69,7 @@ class RankingObjective : public ObjectiveFunction {
                                        const double* score, score_t* lambdas,
                                        score_t* hessians) const = 0;
 
-  virtual const char* GetName() const override = 0;
+  const char* GetName() const override = 0;
 
   std::string ToString() const override {
     std::stringstream str_buf;
@@ -91,6 +91,7 @@ class RankingObjective : public ObjectiveFunction {
   /*! \brief Query boundries */
   const data_size_t* query_boundaries_;
 };
+
 /*!
  * \brief Objective function for Lambdrank with NDCG
  */
@@ -262,12 +263,13 @@ class LambdarankNDCG : public RankingObjective {
   double sigmoid_;
   /*! \brief Normalize the lambdas or not */
   bool norm_;
-  /*! \brief truncation position for max ndcg */
+  /*! \brief Truncation position for max DCG */
   int truncation_level_;
   /*! \brief Cache inverse max DCG, speed up calculation */
   std::vector<double> inverse_max_dcgs_;
   /*! \brief Cache result for sigmoid transform to speed up */
   std::vector<double> sigmoid_table_;
+  /*! \brief Gains for labels */
   std::vector<double> label_gain_;
   /*! \brief Number of bins in simoid table */
   size_t _sigmoid_bins = 1024 * 1024;