code: def forward(
      ctx: FunctionCtx, nat_mean: Tensor, tril_nat_covar: Tensor
  ) -> Tuple[Tensor, Tensor]:
      mu, L = _TrilNaturalToMuVarSqrt._forward(nat_mean, tril_nat_covar)
      ctx.save_for_backward(mu, L, tril_nat_covar)
      return mu, L
  
file_path: gpytorch/gpytorch/variational/tril_natural_variational_distribution.py
imports: from typing import Tuple
  import torch
  from linear_operator.operators import CholLinearOperator, TriangularLinearOperator
  from torch import Tensor
  from torch.autograd.function import FunctionCtx
  from ..distributions import Distribution, MultivariateNormal
  from .natural_variational_distribution import _NaturalToMuVarSqrt, _NaturalVariationalDistribution, _phi_for_cholesky_, _triangular_inverse
label_desc: Use image node_id 2 for calling the _TrilNaturalToMuVarSqrt obj's underlying member method code with example usage: obj.forward(ctx, nat_mean, tril_nat_covar) and returns: mu,  L