\begin{figure}
     \centering
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/citeulike_recall_10.png}
         }
         \caption{Recall@10 on Citeulike-a}
         \label{fig:citeulike_K_J_rec}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/cellphones_recall_10.png}
         }
         \caption{Recall@10 on Cell Phones}
         \label{fig:cellphones_K_J_rec}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/movielen_rec_10.png}
         }
         \caption{Recall@10 on MovieLens}
         \label{fig:movielens_K_J_rec}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/citeulike_ndcg_10.png}
         }
         \caption{NDCG@10 on Citeulike-a}
         \label{fig:citeulike_K_J_ndcg}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/cellphones_ndcg_10.png}
         }
         \caption{NDCG@10 on Cell Phones}
         \label{fig:cellphones_K_J_ndcg}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.32\textwidth}
         \scalebox{1}{
         \includegraphics[width=\textwidth]{figures/num_factors/movielen_ndcg_10.png}
         }
         \caption{NDCG@10 on MovieLens}
         \label{fig:movielens_K_J_ndcg}
     \end{subfigure}
    \caption{\ourmethod's performance w.r.t. $K$ and $J$.}
    \label{fig:K_J_comp}
\end{figure}