code: def _add_rhoa(df, spacing):
      
      df['k'] = redaK.compute_K_analytical(df, spacing=spacing)
      df['rho_a'] = df['r'] * df['k']
      if 'Zt' in df.columns:
          df['rho_a_complex'] = df['Zt'] * df['k']
      return df
docs: a simple wrapper to compute K factors and add rhoa