code: def forward(self, y_dict, design, observation_labels, target_labels):
      pyro.module("posterior_guide", self)
  
      # Returns two dicts from labels -> tensors
      mu, scale_tril = self.get_params(y_dict, design, target_labels)
  
      for l in target_labels:
          w_dist = dist.MultivariateNormal(
              mu[l], scale_tril=scale_tril[l]
          )
          pyro.sample(l, w_dist)
  
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 4 for calling the LinearModelPosteriorGuide obj's underlying member method code with example usage: obj.forward(y_dict, design, observation_labels, target_labels) without return types