improving code comments

Author: Haonan

paddle/gserver/layers/RotateLayer.cpp

@@ -38,7 +38,8 @@ void RotateLayer::forward(PassType passType) {
   size_ = input->getWidth();
   CHECK_GE(size_, height_ * width_);
   CHECK_EQ(size_ % (height_ * width_), 0)
-      << "The input's depth should be an int";
+      << "total size_ is not dividable by (height_ * width_), i.e., "
+      << "channel number should be an integer";
   channels_ = size_ / (height_ * width_);
 
   resizeOutput(batchSize_, size_);

paddle/gserver/layers/RotateLayer.h

@@ -21,7 +21,7 @@ namespace paddle {
 /**
  * A layer for rotating a multi-channel feature map (M x N x C) in the spatial
  * domain
- * The rotation is 90 degrees in clock-wise
+ * The rotation is 90 degrees in clock-wise for each channel
  * \f[
  *   y(j,i,:) = x(M-i-1,j,:)
  * \f]

paddle/gserver/tests/test_LayerGrad.cpp

@@ -1320,9 +1320,10 @@ TEST(Layer, RotateLayer) {
   TestConfig config;
   config.biasSize = 0;
   config.layerConfig.set_type("rotate");
-  const int INPUT_SIZE = 64;  //  height * width * depth
+  const int CHANNEL = 2;
   const int HEIGHT = 8;
   const int WIDTH = 4;
+  const int INPUT_SIZE = HEIGHT * WIDTH * CHANNEL;
   config.layerConfig.set_size(INPUT_SIZE);
   config.layerConfig.set_height(HEIGHT);
   config.layerConfig.set_width(WIDTH);

python/paddle/trainer_config_helpers/layers.py

@@ -1679,8 +1679,8 @@ def trans_layer(input, name=None, layer_attr=None):
 @layer_support()
 def rotate_layer(input, height, width, name=None, layer_attr=None):
     """
-    A layer for rotating 90 degrees (clock-wise), usually used when the input sample
-    is some image or feature map.
+    A layer for rotating 90 degrees (clock-wise) for each feature channel,
+    usually used when the input sample is some image or feature map.
 
     .. math::
        y(j,i,:) = x(M-i-1,j,:)