Removed the requirement that the lisf be non-empty when used to load an

EKM.  Instead, the load() function now will accept non-empty lisf objects
and throw a non-fatal exception.  This behavior should be slightly less
surprising to users, especially since certain degenerate datasets can give
rise to empty lisf objects when you might not expect it.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404111

dlib/svm/empirical_kernel_map.h

@@ -76,12 +76,16 @@ namespace dlib
             const linearly_independent_subset_finder<kernel_type>& lisf
         )
         {
-            // make sure requires clause is not broken
-            DLIB_ASSERT(lisf.size() > 0,
-                "\tvoid empirical_kernel_map::load(linearly_independent_subset_finder)"
-                << "\n\t You have to give a non-empty set of basis_samples"
-                << "\n\t this: " << this
-                );
+            if (lisf.size() == 0)
+            {
+                std::ostringstream sout;
+                sout << "An empty linearly_independent_subset_finder was supplied to the\n"
+                     << "empirical_kernel_map::load() function.  One reason this might occur\n"
+                     << "is if your dataset contains only zero vectors (or vectors \n"
+                     << "approximately zero).\n";
+                clear();
+                throw empirical_kernel_map_error(sout.str());
+            }
 
             kernel = lisf.get_kernel();
             weights = trans(chol(lisf.get_inv_kernel_marix()));

dlib/svm/empirical_kernel_map_abstract.h

@@ -152,8 +152,6 @@ namespace dlib
             const linearly_independent_subset_finder<kernel_type>& lisf
         );
         /*!
-            requires
-                - lisf.dictionary_size() > 0
             ensures
                 - #out_vector_size() == lisf.dictionary_size() 
                 - #basis_size() == lisf.dictionary_size()
@@ -169,7 +167,8 @@ namespace dlib
                     - for all valid i: (*this)[i] == lisf[i]
             throws
                 - empirical_kernel_map_error
-                    This exception is thrown if we are unable to create a kernel map.
+                    This exception is thrown if we are unable to create a kernel map.  
+                    E.g.  if the lisf.size() == 0.  
                     If this happens then this object will revert back to its initial value.
         !*/