\draw [-,ublue] (0,0) .. controls (2,0) and (3,-1.0)..(3,-1.5) .. controls (3,-2.2) and (2,-1.75)..(1.5,-1.65)..controls (1.5,-1.65) and (0.5,-1.45)..(0,-1.45)..controls (-0.5,-1.45) and (-1.5,-1.65)..(-1.5,-1.65)..controls (-2,-1.75)and (-3,-2.2).. (-3,-1.5)..controls (-3,-1.0) and (-2,0)..(0,0);
\draw [-,ublue] (0,0.5)..controls (2,0.5) and (4,-1.0).. (4,-1.7)..controls(4,-2.6)and (3,-2.3)..(2,-2.05)..controls (2,-2.05) and (1,-1.80)..(0,-1.80)..controls (-1,-1.80)and (-2,-2.05)..(-2,-2.05)..controls(-3,-2.3)and(-4,-2.6)..(-4,-1.7)..controls(-4,-1.0)and (-2,0.5)..(0,0.5);
\draw[-,ublue](0,1.0)..controls(3,1.0) and (5,-1.0)..(5,-1.9)..controls (5,-3.2)and (4,-2.7)..(3,-2.5)..controls (3,-2.5) and (2,-2.20)..(0,-2.15)..controls (-2,-2.20)and (-3,-2.5)..(-3,-2.5)..controls (-4,-2.7) and (-5,-3.2) ..(-5,-1.9)..controls (-5,-1.0) and (-3,1.0)..(0,1.0);
\draw[-,ublue] (0,-0.3)..controls (1.5,-0.3)and (2.5,-1.0)..(2.5,-1.4)..controls(2.5,-1.8)and (2,-1.55)..(1.5,-1.45) ..controls (1.5,-1.45) and (0.5,-1.25)..(0,-1.25) .. controls(-0.5,-1.25)and (-1.5,-1.45)..(-1.5,-1.45)..controls(-2,-1.55)and (-2.5,-1.8) ..(-2.5,-1.4)..controls(-2.5,-1.0) and (-1.5,-0.3)..(0,-0.3);
\draw[-,ublue](0,-0.5)..controls (1.0,-0.5) and (1.9,-0.8)..(1.9,-1.3)..controls(1.9,-1.5)and (1.5,-1.3)..(1.0,-1.2) ..controls(1.0,-1.2) and (0.5,-1.1)..(0,-1.1)..controls(-0.5,-1.1) and (-1.0,-1.2)..(-1.0,-1.2)..controls (-1.5,-1.3)and (-1.9,-1.5)..(-1.9,-1.3) ..controls(-1.9,-0.8)and (-1.0,-0.5) ..(0,-0.5);
\draw[-,ublue](0,-0.7)..controls(1.0,-0.7) and (1.4,-0.9)..(1.4,-1.1) .. controls(1.4,-1.25) and (1.2,-1.15)..(1.0,-1.1)..controls(1.0,-1.1) and (0.5,-0.95)..(0,-0.95)..controls(-0.5,-0.95)and (-1.0,-1.1) ..(-1.0,-1.1)..controls(-1.2,-1.15) and (-1.4,-1.25)..(-1.4,-1.1)..controls(-1.4,-0.9) and (-1.0,-0.7)..(0,-0.7);
\draw[-,ublue](0,-0.75)..controls(0.7,-0.75)and (1.0,-0.9)..(1.0,-1.0)..controls(1.0,-1.05) and (0.9,-1.05)..(0.7,-1.0)..controls(0.5,-0.95)and (0.3,-0.9)..(0,-0.9)..controls(-0.3,-0.9)and (-0.5,-0.95)..(-0.7,-1.0)..controls(-0.9,-1.05)and (-1.0,-1.05)..(-1.0,-1.0) ..controls(-1.0,-0.9)and (-0.7,-0.75)..(0,-0.75);
\draw[-,ublue](0,-0.8)..controls(0.5,-0.8) and (0.6,-0.85)..(0.6,-0.9)..controls(0.6,-0.93)and (0.5,-0.91)..(0.3,-0.88)..controls(0.2,-0.87)and (0.1,-0.86)..(0,-0.86)..controls(-0.1,-0.86)and(-0.2,-0.87)..(-0.3,-0.88)..controls(-0.5,-0.91) and(-0.6,-0.93) ..(-0.6,-0.9)..controls(-0.6,-0.85)and (-0.5,-0.8)..(0,-0.8);
\node [anchor=north] (labelb) at (0,-3) {\footnotesize{(b)Momentum梯度下降算法更加``平滑''地更新}};