docs: def define_residues_for_plotting_traj(self, analysis_cutoff):
          """
          Since plotting all residues that have made contact with the ligand over a lenghty
          simulation is not always feasible or desirable. Therefore, only the residues that
          have been in contact with ligand for a long amount of time will be plotted in the
          final image.
  
          The function first determines the fraction of time each residue spends in the
          vicinity of the ligand for each trajectory. Once the data is processed, analysis
          cutoff decides whether or not these residues are plotted based on the total
          frequency this residue has spent in the vicinity of the ligand. The analysis
          cutoff is supplied for a single trajectory and is therefore multiplied.
  
          Takes:
              * analysis_cutoff * - a fraction (of time) a residue has to spend in the
              vicinity of the ligand for a single traj
          Output:
              * self.frequency * - frequency per residue per trajectory
              * topol_data.dict_of_plotted_res * - the residues that should be plotted in
              the final image with the frequency for each trajectory (used for plotting)
          """
          self.residue_counts_fraction = {}
          #Calculate the fraction of time a residue spends in each simulation
          for traj in self.residue_counts:
              self.residue_counts_fraction[traj] = {residue:float(values)/len(self.contacts_per_timeframe[traj]) for residue,values in self.residue_counts[traj].items()}
  
          for traj in self.residue_counts_fraction:
              for residue in self.residue_counts_fraction[traj]:
                  self.frequency[residue].append(self.residue_counts_fraction[traj][residue])
  
          self.topology_data.dict_of_plotted_res = {i:self.frequency[i] for i in self.frequency if sum(self.frequency[i])>(int(len(self.trajectory))*analysis_cutoff)}
  
          assert len(self.topology_data.dict_of_plotted_res)!=0,"Nothing to draw for this ligand:(residue number: "+ str(self.topology_data.universe.ligand.resids[0]) +" on the chain "+ str(self.topology_data.universe.ligand.segids[0]) +") - try reducing the analysis cutoff."