损失函数画图
Hinge loss function：
\[H(z) = max(0,1-z)\]
$\psi$-learning loss function:
\[{\phi _s}(z) = \left\{ {\begin{array}{*{20}{c}}
s&{z < 0}\\
0&{z \ge 0}
\end{array}} \right.\]
Normalized Sigmoid loss:
\[{P_t}(z) = 1 - \tanh (tz)\]
Ramp loss function:
\[{R_s}(z) = \left\{ {\begin{array}{*{20}{c}}
0&{z > 0}\\
{1 - z}&{0 \le z \le 1}\\
{1 - s}&{z > 1}
\end{array}} \right.\]
%plot loss function
%define the loss function
