code: def forward(self, x):
      x = self.backbone(x).flatten(start_dim=1)
      z = self.projection_head(x)
      return z
  
file_path: lightly/examples/pytorch_lightning_distributed/barlowtwins.py
imports: import pytorch_lightning
  import torch
  import torchvision
  from torch import nn
  from lightly.loss import BarlowTwinsLoss
  from lightly.models.modules import BarlowTwinsProjectionHead
  from lightly.transforms.byol_transform import BYOLTransform, BYOLView1Transform, BYOLView2Transform
label_desc: Use image node_id 2 for calling the BarlowTwins obj's underlying member method code with example usage: obj.forward(x) and returns: z