code: def traceplot(fit, pars, dtypes, **kwargs):
      
      # FIXME: eventually put this in the StanFit object
      # FIXME: write a to_pymc(_trace) function
      # Deprecation warning added in PyStan 2.18
      logger.warning("Deprecation warning."\
                     " In future, use ArviZ library (`pip install arviz`)")
      try:
          from pystan.external.pymc import plots
      except ImportError:
          logger.critical("matplotlib required for plotting.")
          raise
      if pars is None:
          pars = list(fit.model_pars) + ["lp__"]
      values = fit.extract(dtypes=dtypes, pars=pars, permuted=False)
      values = {key : arr.reshape(-1, int(np.multiply.reduce(arr.shape[2:])), order="F") for key, arr in values.items()}
      return plots.traceplot(values, pars, **kwargs)
docs: Use pymc's traceplot to display parameters.
  
      Additional arguments are passed to pymc.plots.traceplot.