Add sub2ind comment.

src/Function2D.h

@@ -148,6 +148,13 @@ namespace Aurora
 
     Matrix dot(const Matrix &aMatrix, const Matrix &aOther, FunctionDirection direction = Column);
 
+    /**
+     * 转换下标为索引值
+     * @attention 索引值按照其实为1与matlab对应，在C++中使用需要-1
+     * @param aVMatrixSize
+     * @param aSliceIdxs
+     * @return
+     */
     Matrix sub2ind(const Matrix &aVMatrixSize, std::initializer_list<Matrix> aSliceIdxs);
     
 };