code: def calcR2(predTst, yTest, axis=0):
      
      rss = np.sum((yTest - predTst) ** 2, axis=axis)
      tss = np.sum((yTest - yTest.mean()) ** 2, axis=axis)
  
      return 1 - rss/tss
docs: calculate coefficient of determination. Assumes that axis=0 is time
  
          Parameters
          ----------
          predTst : np.array, predicted reponse for yTest
          yTest : np.array, acxtually observed response for yTest
          Returns
          -------
          aryFunc : np.array
              R2