class_docstr: Naive Marsaglia & Tsang rejection sampler for standard Gamma distibution.
  This assumes `concentration >= 1` and does not boost `concentration` or augment shape.
code: def log_prob(self, x):
      return self._standard_gamma.log_prob(x)
  
imports: import torch
  from pyro.distributions.rejector import Rejector
  from pyro.distributions.score_parts import ScoreParts
  from pyro.distributions.torch import Beta, Dirichlet, Gamma, Normal
  from pyro.distributions.util import copy_docs_from, weakmethod
label_desc: Use image node_id 6 for calling the RejectionStandardGamma obj's underlying member method code with example usage: obj.log_prob(x) and returns: self