From f9805be8566c329bf62aabdc89325ddfb7c682c1 Mon Sep 17 00:00:00 2001
From: Davis King <davis@dlib.net>
Date: Mon, 17 Dec 2012 20:33:34 -0500
Subject: [PATCH] Fixed a bug which triggered when the last weight was forced
 to 1.

---
 dlib/svm/svm_c_linear_dcd_trainer.h | 40 ++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/dlib/svm/svm_c_linear_dcd_trainer.h b/dlib/svm/svm_c_linear_dcd_trainer.h
index f519f8e39..64ca66e44 100644
--- a/dlib/svm/svm_c_linear_dcd_trainer.h
+++ b/dlib/svm/svm_c_linear_dcd_trainer.h
@@ -301,7 +301,7 @@ namespace dlib
 
                 for (long i = new_idx; i < x.size(); ++i)
                 {
-                    Q.push_back(dlib::dot(x(i),x(i)));
+                    Q.push_back(length_squared(x(i)));
 
                     if (have_bias)
                     {
@@ -318,6 +318,44 @@ namespace dlib
                     w(dims-1) = 1;
             }
 
+            template <typename T>
+            typename enable_if<is_matrix<T>,scalar_type>::type length_squared (const T& x) const
+            {
+                if (!last_weight_1)
+                {
+                    return dlib::dot(x,x);
+                }
+                else
+                {
+                    // skip the last dimension
+                    return dlib::dot(colm(x,0,x.size()-1), 
+                                     colm(x,0,x.size()-1));
+                }
+
+            }
+
+            template <typename T>
+            typename disable_if<is_matrix<T>,scalar_type>::type length_squared (const T& x) const
+            {
+                if (!last_weight_1)
+                {
+                    return dlib::dot(x,x);
+                }
+                else
+                {
+                    scalar_type temp = 0;
+                    typename T::const_iterator i;
+                    for (i = x.begin(); i != x.end(); ++i)
+                    {
+                        // skip the last dimension
+                        if (static_cast<long>(i->first) < dims-1)
+                            temp += i->second*i->second;
+                    }
+                    return temp;
+                }
+            }
+
+
             bool did_init;
             bool have_bias;
             bool last_weight_1;