class_docstr: LinexLoss is an asymmetric loss talked about in
  https://www.scirp.org/journal/paperinformation.aspx?paperid=97986
code: def forward(self, y_hat, y):
      delta = y - y_hat
      loss = self.b * (torch.exp(self.a * delta) - self.a * delta - 1)
      return torch.mean(loss)
  
imports: import torch
  import torch.nn
  from bigdl.nano.utils.common import invalidInputError
label_desc: Use image node_id 2 for calling the LinexLoss obj's underlying member method code with example usage: obj.forward(y_hat, y) and returns: torch