Cookbook for chi_square distance (#4324)

* updated csv_file in chi_square.sg to new api and wrote a cookbook for the chi_square distance

doc/cookbook/source/examples/distance/chi_square.rst

@@ -0,0 +1,35 @@
+===================
+Chi Square Distance
+===================
+
+The Chi Square Distance for real valued features :math:`\bf{x},\bf{x'} \in \mathbb{R}^{n}` extends the concept of :math:`\chi^{2}` distance to negative values.
+This distance is calculated by the equation:
+
+.. math::
+
+    d(\bf{x},\bf{x'}) = \sum_{i=1}^{n}\frac{(x_{i}-x'_{i})^2}{|x_{i}|+|x'_{i}|}
+
+-------
+Example
+-------
+
+We first create some sample data. So we instantiate CDenseFeatures containing the sample data.
+
+.. sgexample:: chi_square.sg:create_features
+
+We create an instance of :sgclass:`CChiSquareDistance` by passing it the sample data :sgclass:`CDenseFeatures`.
+
+.. sgexample:: cosine.sg:create_instance
+
+The distance matrix can be extracted as follows:
+
+.. sgexample:: chi_square.sg:extract_distance
+
+We can use the same instance with new :sgclass:`CDenseFeatures` to compute asymmetrical distance as follows:
+
+.. sgexample:: chi_square.sg:refresh_distance
+
+----------
+References
+----------
+:wiki:`Chi-squared_test`

examples/meta/src/distance/chi_square.sg

@@ -1,5 +1,5 @@
-CSVFile f_feats_a("../../data/fm_train_real.dat")
-CSVFile f_feats_b("../../data/fm_test_real.dat")
+File f_feats_a = csv_file("../../data/fm_train_real.dat")
+File f_feats_b = csv_file("../../data/fm_test_real.dat")
 
 #![create_features]
 Features features_a = features(f_feats_a)