docs: def fit(self):
          """Fit MCMC AgeDepthModel"""
          self._mcmcfit = self.mcmcsetup.run()
          self._mcmcfit.burnin(self.burnin)
          dmin = min(self._mcmcfit.depth_segments)
          dmax = max(self._mcmcfit.depth_segments)
          self._thick = (dmax - dmin) / len(self.mcmcfit.depth_segments)
          self._depth = np.arange(dmin, dmax + 0.001)
          self._age_ensemble = np.array([self.agedepth(d=dx) for dx in self.depth])