| Hugging | Hugging |
| OPC | The online principal components can handle data sets that are updated in real time and streaming data. |
| PC | The traditional principal component method. This method can estimate the eigen space of the data set. |
| PSA | Prostate Specific Antigen |
| SOPC | The sparse online principal component can not only process the real-time updated data set and stream data set, but also obtain the sparse solution of the updated data set. |
| SPC | The sparse principal component can obtain sparse solutions of the eigenmatrix to better explain the relationship between principal components and original variables. |