From ec14d3275664ab6b6d93b716904078f72b9d64f1 Mon Sep 17 00:00:00 2001
From: tqchen <tianqi.tchen@gmail.com>
Date: Wed, 30 Apr 2014 22:11:26 -0700
Subject: [PATCH] add softmax

---
 regrank/xgboost_regrank_obj.h   |  1 +
 regrank/xgboost_regrank_obj.hpp | 65 +++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/regrank/xgboost_regrank_obj.h b/regrank/xgboost_regrank_obj.h
index cc2f1eb2b..a494aa763 100644
--- a/regrank/xgboost_regrank_obj.h
+++ b/regrank/xgboost_regrank_obj.h
@@ -107,6 +107,7 @@ namespace xgboost{
         IObjFunction* CreateObjFunction( const char *name ){
             if( !strcmp("reg", name ) ) return new RegressionObj();
             if( !strcmp("rank", name ) ) return new PairwiseRankObj();
+            if( !strcmp("softmax", name ) ) return new SoftmaxObj();
             utils::Error("unknown objective function type");
             return NULL;
         }
diff --git a/regrank/xgboost_regrank_obj.hpp b/regrank/xgboost_regrank_obj.hpp
index 45f05dd2b..fb20f68a0 100644
--- a/regrank/xgboost_regrank_obj.hpp
+++ b/regrank/xgboost_regrank_obj.hpp
@@ -47,6 +47,71 @@ namespace xgboost{
         };
     };
 
+    namespace regrank{
+        // simple softmax rak
+        class SoftmaxObj : public IObjFunction{
+        public:
+            SoftmaxObj(void){
+            }
+            virtual ~SoftmaxObj(){}
+            virtual void SetParam(const char *name, const char *val){
+            }
+            virtual void GetGradient(const std::vector<float>& preds,  
+                                     const DMatrix::Info &info,
+                                     int iter,
+                                     std::vector<float> &grad, 
+                                     std::vector<float> &hess ) {
+                grad.resize(preds.size()); hess.resize(preds.size());
+                const std::vector<unsigned> &gptr = info.group_ptr;
+                utils::Assert( gptr.size() != 0 && gptr.back() == preds.size(), "rank loss must have group file" );
+                const unsigned ngroup = static_cast<unsigned>( gptr.size() - 1 );
+
+                #pragma omp parallel
+                {
+                    std::vector< float > rec;                    
+                    #pragma for schedule(static)
+                    for (unsigned k = 0; k < ngroup; ++k){
+                        rec.clear();
+                        int nhit = 0;
+                        for(unsigned j = gptr[k]; j < gptr[k+1]; ++j ){
+                            rec.push_back( preds[j] );
+                            grad[j] = hess[j] = 0.0f;
+                            nhit += info.labels[j];
+                        }
+                        Softmax( rec );
+                        if( nhit == 1 ){
+                            for(unsigned j = gptr[k]; j < gptr[k+1]; ++j ){
+                                float p = rec[ j - gptr[k] ];
+                                grad[j] = p - info.labels[j];
+                                hess[j] = 2.0f * p * ( 1.0f - p );
+                            }  
+                        }else{
+                            utils::Assert( nhit == 0, "softmax does not allow multiple labels" );
+                        }
+                    }
+                }
+            }
+            virtual const char* DefaultEvalMetric(void) {
+                return "pre@1";
+            }            
+        private:
+            inline static void Softmax( std::vector<float>& rec ){
+                float wmax = rec[0];
+                for( size_t i = 1; i < rec.size(); ++ i ){
+                    wmax = std::max( rec[i], wmax );
+                }
+                double wsum = 0.0f;
+                for( size_t i = 0; i < rec.size(); ++ i ){
+                    rec[i] = expf(rec[i]-wmax);
+                    wsum += rec[i];
+                }
+                for( size_t i = 0; i < rec.size(); ++ i ){
+                    rec[i] /= wsum;
+                }                
+            }
+        };
+    };
+
     namespace regrank{
         // simple pairwise rank 
         class PairwiseRankObj : public IObjFunction{