code: def linear_model_formula(self, y, design, target_labels):
      if self.use_softplus:
          mu = {
              l: rmv(self.softplus(self.regressor[l]), y)
              for l in target_labels
          }
      else:
          mu = {l: rmv(self.regressor[l], y) for l in target_labels}
      scale_tril = {l: rtril(self.scale_tril[l]) for l in target_labels}
  
      return mu, scale_tril
  
imports: from contextlib import ExitStack
  import torch
  from torch import nn
  import pyro
  import pyro.distributions
  from pyro import poutine
  from pyro.contrib.util import iter_plates_to_shape, lexpand, rmv, rtril, rvv, tensor_to_dict
  from pyro.ops.linalg import rinverse
label_desc: Use image node_id 3 for calling the LinearModelPosteriorGuide obj's underlying member method code with example usage: obj.linear_model_formula(y, design, target_labels) and returns: mu,  scale_tril