Merge branch 'marioskogias-master' into 'master'

[doc] Explain train data size

See merge request !6

bob/learn/mlp/backprop.cpp

@@ -390,6 +390,9 @@ thrown.\n\
    \n\
    In BackProp, training is done in batches. You should set the batch\n\
    size properly at class initialization or use setBatchSize().\n\
+   The number of rows in the input should be in accordance with the\n\
+   set batch size. If the batch size currently set is incompatible\n\
+   with the given data an exception is raised.\n\
 \n\
 .. note::\n\
    \n\

doc/guide.rst

@@ -108,7 +108,8 @@ MLPs can be `trained` through backpropagation [2]_, which is a supervised
 learning technique. This training procedure requires a set of features with
 labels (or targets). Using |project|, this is passed to the `train()` method of
 available MLP trainers in two different 2D `NumPy`_ arrays, one for the input
-(features) and one for the output (targets).
+(features) and one for the output (targets). The number of rows in those two
+2D arrays should be equal to the batch size set when creating the model.
 
 .. doctest::
    :options: +NORMALIZE_WHITESPACE