some notes

source/network/XBackwardMath.cpp

@@ -830,6 +830,7 @@ void XMathGrad::GradSign(XTensor * node)
     CheckNTErrors(income.tailNum == 1, "Wrong input tensor number for SIGN!");
 
     // we do nothing here
+    // TODO: set grad = 0 if the node is the only child
 
     node->visitMark = NODE_FINISHED;
 }
@@ -848,6 +849,7 @@ void XMathGrad::GradRound(XTensor * node)
     CheckNTErrors(income.tailNum == 1, "Wrong input tensor number for ROUND!");
 
     // we do nothing here
+    // TODO: set grad = 0 if the node is the only child
 
     node->visitMark = NODE_FINISHED;
 }