class_docstr: Non-normalized Gamma distribution.
  
      Gamma(concentration, rate) ~ (concentration - 1) * log(s) - rate * s
code: def __init__(self, log_normalizer, concentration, rate):
      self.log_normalizer = log_normalizer
      self.concentration = concentration
      self.rate = rate
  
imports: import math
  import torch
  from torch.distributions.utils import lazy_property
  from torch.nn.functional import pad
  from pyro.distributions.multivariate_studentt import MultivariateStudentT
  from pyro.distributions.torch import MultivariateNormal
  from pyro.distributions.util import broadcast_shape
  from pyro.ops.tensor_utils import precision_to_scale_tril
label_desc: Use image node_id 1 to create a new Gamma object  with example: obj = Gamma(log_normalizer, concentration, rate)