title: Error in due loop of ufunc does not support argument 0 of type str which has no callable log method
body: <p>When I use the below log function, i am getting the following error message in my jupyter notebook.
  data1 = np.log(mdata).diff().dropna()
  I tried to do cast but unable to get rid of this issue.
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  AttributeError: 'str' object has no attribute 'log'</p>
  <pre><code>The above exception was the direct cause of the following exception:
  
  TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-13-b6f1878a7619&gt; in &lt;module&gt;
  ----&gt; 1 data1 = np.log(mdata).diff().dropna()
  
  TypeError: loop of ufunc does not support argument 0 of type str which has no callable log method
  </code></pre>
  <p>mdata:</p>
  <pre><code>          Field1    Field2  Field3  Field4
  TS              
  2020-11-02 00:43:58.500 1595000 849332  205 69
  2020-11-02 00:43:58.500 1408000 820332  198 51
  2020-11-02 00:43:58.500 1770000 926054  213 56
  2020-11-02 00:43:58.500 1760000 1002332 216 72
  2020-11-02 00:43:58.500 1850000 957054  213 59
  ... ... ... ... ...
   
  </code></pre>
  <p>mdata.index:</p>
  <pre><code>DatetimeIndex(['2020-11-02 00:43:58.500000', '2020-11-02 00:43:58.500000',
                 '2020-11-02 00:43:58.500000', '2020-11-02 00:43:58.500000',
                 '2020-11-02 00:43:58.500000', '2020-11-02 00:43:58.500000',
                 '2020-11-02 00:43:58.500000', '2020-11-02 00:43:58.500000',
                 '2020-11-02 00:43:58.600000', '2020-11-02 00:43:58.600000',
                 ...
  
                 '2020-11-02 00:44:00.400000', '2020-11-02 00:44:00.500000'],
                dtype='datetime64[ns]', name='TS', length=199, freq=None)
  </code></pre>
  <p>Complete code is</p>
  <pre><code>df1 = pd.read_csv('inputdata.csv')
  cols = ['Field1','Field2','Field3','Field4'] 
  data_x = pd.to_datetime(data_x)
  mdata = df1[cols]
  mdata.index = pd.DatetimeIndex(data_x)
  data1 = np.log(mdata).diff().dropna()
  
  The following statements are not executed due to the issue in the above statement
  
  model = VAR(data)
  results = model.fit(2)
  results.summary()
  </code></pre>