I need help interpreting an expression I have the following formula: > $$\min_{\beta_0,\beta}\sum_{i=1}^n[1-y_if(x_i)]_++\frac1{2C}\lVert \beta\rVert^2$$ What does the bracket with the subscripted plus mean? I greatly appreciate your help. Thank you.

Quite often, $x_+$ indicates $\max\\{x,0\\}$ and $x_-$ indicates $-\min\\{x,0\\}=(-x)_+$. Under these conventions $$\lvert x\rvert=x_++x_-\\\ x=x_+-x_-$$