Clarify batch norm parameter documentation.

diff --git a/src/caffe/proto/caffe.proto b/src/caffe/proto/caffe.proto
index a145c54..02e0ddf 100644 (file)
--- a/src/caffe/proto/caffe.proto
+++ b/src/caffe/proto/caffe.proto
@@ -502,11 +502,21 @@ message ConcatParameter {
 }
 
 message BatchNormParameter {
-  // If false, accumulate global mean/variance values via a moving average. If
-  // true, use those accumulated values instead of computing mean/variance
-  // across the batch.
+  // If false, normalization is performed over the current mini-batch
+  // and global statistics are accumulated (but not yet used) by a moving
+  // average.
+  // If true, those accumulated mean and variance values are used for the
+  // normalization.
+  // By default, it is set to false when the network is in the training
+  // phase and true when the network is in the testing phase.
   optional bool use_global_stats = 1;
-  // How much does the moving average decay each iteration?
+  // What fraction of the moving average remains each iteration?
+  // Smaller values make the moving average decay faster, giving more
+  // weight to the recent values.
+  // Each iteration updates the moving average @f$S_{t-1}@f$ with the
+  // current mean @f$ Y_t @f$ by
+  // @f$ S_t = (1-\beta)Y_t + \beta \cdot S_{t-1} @f$, where @f$ \beta @f$
+  // is the moving_average_fraction parameter.
   optional float moving_average_fraction = 2 [default = .999];
   // Small value to add to the variance estimate so that we don't divide by
   // zero.