docs: def LMTD(Thi, Tho, Tci, Tco, counterflow=True):
      r'''Returns the log-mean temperature difference of an ideal counterflow
      or co-current heat exchanger.
  
      .. math::
          \Delta T_{LMTD}=\frac{\Delta T_1-\Delta T_2}{\ln(\Delta T_1/\Delta T_2)}
  
          \text{For countercurrent:      } \\
          \Delta T_1=T_{h,i}-T_{c,o}\\
          \Delta T_2=T_{h,o}-T_{c,i}
  
          \text{Parallel Flow Only:} \\
          {\Delta T_1=T_{h,i}-T_{c,i}}\\
          {\Delta T_2=T_{h,o}-T_{c,o}}
  
      Parameters
      ----------
      Thi : float
          Inlet temperature of hot fluid, [K]
      Tho : float
          Outlet temperature of hot fluid, [K]
      Tci : float
          Inlet temperature of cold fluid, [K]
      Tco : float
          Outlet temperature of cold fluid, [K]
      counterflow : bool, optional
          Whether the exchanger is counterflow or co-current
  
      Returns
      -------
      LMTD : float
          Log-mean temperature difference [K]
  
      Notes
      -----
      Any consistent set of units produces a consistent output.
  
      Examples
      --------
      Example 11.1 in [1]_.
  
      >>> LMTD(100., 60., 30., 40.2)
      43.200409294131525
      >>> LMTD(100., 60., 30., 40.2, counterflow=False)
      39.75251118049003
  
      References
      ----------
      .. [1] Bergman, Theodore L., Adrienne S. Lavine, Frank P. Incropera, and
         David P. DeWitt. Introduction to Heat Transfer. 6E. Hoboken, NJ:
         Wiley, 2011.
      '''
      if counterflow:
          dTF1 = Thi-Tco
          dTF2 = Tho-Tci
      else:
          dTF1 = Thi-Tci
          dTF2 = Tho-Tco
      return (dTF2 - dTF1)/log(dTF2/dTF1)