code: def update(self, params, values):
          
          # radparams = self.param_radii()
          params = listify(params)
          values = listify(values)
          for i, p in enumerate(params):
              # if (p in radparams) & (values[i] < 0):
              if (p[-2:] == '-a') and (values[i] < 0):
                  values[i] = 0.0
          super(PlatonicSpheresCollection, self).update(params, values)
docs: Calls an update, but clips radii to be > 0