I really don't understand what dose the psi class do, any explain would be helpful

[ChiHanfeng]

Dose the psi class do the pooling operation mentioned in the paper? If it is, why the x1 should be pooled, which is directly summed to Fx2 in the paper?

[jhjacobsen]

Figure 2 in the paper illustrates its functionality. Please have a look, it should give you a good understanding of what it does.