code: def forward(self, sim_matrix):
      logpt = F.log_softmax(sim_matrix, dim=-1)
      logpt = torch.diag(logpt)
      nce_loss = -logpt
      sim_loss = nce_loss.mean()
      return sim_loss
  
file_path: towhee/towhee/models/clip4clip/until_module.py
imports: import torch
  import torch.nn.functional
  from torch import nn
label_desc: Use image node_id 1 for calling the CrossEn obj's underlying member method code with example usage: obj.forward(sim_matrix) and returns: sim_loss