code: def validation_epoch(self, epoch_info, source: 'vel.api.Source'):
          
          self.eval()
  
          iterator = tqdm.tqdm(source.val_loader(), desc="Validation", unit="iter", file=sys.stdout)
  
          with torch.no_grad():
              for batch_idx, (data, target) in enumerate(iterator):
                  batch_info = BatchInfo(epoch_info, batch_idx)
  
                  batch_info.on_validation_batch_begin()
                  self.feed_batch(batch_info, data, target)
                  batch_info.on_validation_batch_end()
docs: Run a single evaluation epoch