code: def run(self, x=None):
          r
          logger.info('Running ReactiveTransport')
          # Create S1 & S1 for 1st Picard's iteration
          if x is None:
              x = np.zeros(shape=[self.Np, ], dtype=float)
          self[self.settings['quantity']] = x
          self._update_physics()
  
          x = self._run_reactive(x=x)
          self[self.settings['quantity']] = x
docs: r"""
          Builds the A and b matrices, and calls the solver specified in the
          ``settings`` attribute.
  
          Parameters
          ----------
          x : ND-array
              Initial guess of unknown variable