fix: resolve LSI dimension mismatch with native Ruby SVD

Native Ruby SVD returns transposed matrix dimensions when
row_size < column_size (common case: few terms, many documents).
This caused ExceptionForMatrix::ErrDimensionMismatch during
classification with 10+ similar documents.

Two changes:
- Transpose reduced matrix when dimensions don't match input
- Iterate over column_size (documents) not row_size (terms)

Fixes #72

Author: cardmagic

lib/classifier/lsi.rb

@@ -144,7 +144,7 @@ def build_index(cutoff = 0.75)
         tdm = Matrix.rows(tda).trans
         ntdm = build_reduced_matrix(tdm, cutoff)
 
-        ntdm.row_size.times do |col|
+        ntdm.column_size.times do |col|
           next unless doc_list[col]
 
           column = ntdm.column(col)
@@ -332,7 +332,15 @@ def build_reduced_matrix(matrix, cutoff = 0.75)
         s[ord] = 0.0 if s[ord] < s_cutoff
       end
       # Reconstruct the term document matrix, only with reduced rank
-      u * (self.class.gsl_available ? GSL::Matrix : ::Matrix).diag(s) * v.trans
+      result = u * (self.class.gsl_available ? GSL::Matrix : ::Matrix).diag(s) * v.trans
+
+      # Native Ruby SVD returns transposed dimensions when row_size < column_size
+      # Ensure result matches input dimensions
+      if !self.class.gsl_available && result.row_size != matrix.row_size
+        result = result.trans
+      end
+
+      result
     end
 
     def node_for_content(item, &block)