code: def linear_model():
      return known_covariance_linear_model(
          coef_means=torch.tensor(0.0),
          coef_sds=torch.tensor([1.0, 1.5]),
          observation_sd=torch.tensor(1.0),
      )
  
imports: import pytest
  import torch
  import pyro
  import pyro.distributions
  import pyro.optim
  from pyro.contrib.oed.eig import donsker_varadhan_eig, laplace_eig, lfire_eig, marginal_eig, marginal_likelihood_eig, nmc_eig, posterior_eig, vnmc_eig
  from pyro.contrib.oed.glmm import known_covariance_linear_model
  from pyro.contrib.oed.glmm.guides import LinearModelLaplaceGuide
  from pyro.contrib.oed.util import linear_model_ground_truth
  from pyro.contrib.util import rmv, rvv
  from pyro.infer import Trace_ELBO
  from tests.common import assert_equal
label_desc: Use image node_id 1 for calling a global function with example usage: linear_model() and returns: known_covariance_linear_model