DOC: Update Cookbook wirth new modes

Documentation/Cookbook/rst/recipes/pbclassif.rst

@@ -104,7 +104,13 @@ There are several strategies to compute those sampling rates:
   of samples, which is user-defined.
 * **Smallest class strategy:** The class with the least number of samples
   will be fully sampled. All other classes will be sampled with the
-  same number of samples.
+same number of samples.
+* **Percent strategy:** Each class will be sampled with a user-defined
+  percentage (same value for all classes) of samples available in this
+class.
+* **Total strategy:** A global number of samples to generate is
+  divided proportionally among each class (classes proportions are
+  enforced).
 * **Take all strategy:** Take all the available samples
 * **By class strategy:** Set a target number of samples for each
   class. The number of samples for each class is read from a CSV file.
@@ -246,7 +252,23 @@ image.
   - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
     :math:`Ni( c ) = M_i(c)` where :math:`M_i(c)` is the custom requested number of
     samples for each image :math:`i` and each class :math:`c`
-  
+
+* **Strategy = percent**
+  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
+    :math:`N_i( c ) = p * T_i(c)` where :math:`p` is the user-defined percentage
+  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
+    :math:`N_i( c ) = p * sum_k(Tk(c)]/L` where :math:`p` is the user-defined percentage
+  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
+    :math:`Ni( c ) = p(i) * T_i(c)` where :math:`p(i)` is the user-defined percentage for image :math:`i`
+
+* **Strategy = total**
+  - *Mode = proportional:* For each image :math:`i` and each class :math:`c`,
+    :math:`N_i( c ) = total * (sum_k(Ti(k))/sum_kl(Tl(k))) * (Ti(c)/sum_k(Ti(k)))` where :math:`total` is the total number of samples specified
+  - *Mode = equal:* For each image :math:`i` and each class :math:`c`,
+    :math:`N_i( c ) = (total / L) * (Ti(c)/sum_k(Ti(k)))` where :math:`total` is the total number of samples specified
+  - *Mode = custom:* For each image :math:`i` and each class :math:`c`,
+  :math:`Ni( c ) = total(i) * (Ti(c)/sum_k(Ti(k)))` where :math:`total(i)` is the total number of samples specified for image :math:`i`
+    
 * **Strategy = smallest class**
       
   - *Mode = proportional:* the smallest class is computed globally, then this smallest size is used for the strategy constant+proportional