AutoEncoder does not generate a symmetric model

Created by: whyisyoung

Hi,

I plotted the model when printing the model summary: https://github.com/yzhao062/pyod/blob/da68f50ee79bd74777d2d406cac6dcfad412e599/pyod/models/auto_encoder.py#L187

And it seems that you added an extra layer at the beginning with the same dimension as the input. I don't know why this is required because it would generate an asymmetric model. Here is the model I printed out:

The final dimension would be like 645-645-100-100-500-9-500-100-100-645.

I think the problem might be caused by this line: https://github.com/yzhao062/pyod/blob/da68f50ee79bd74777d2d406cac6dcfad412e599/pyod/models/auto_encoder.py#L224

The performance is similar after I commented out the above line.

Please correct me if I miss something! Thanks!