title: "RuntimeWarning: invalid value encountered in double_scalars" error occurs when taking cube root in python3
body: <pre><code>from numpy import cos
  from tabulate import tabulate
  
  def f(x):
      return (cos(x))**(1./3)
  
  table=[i for i in range(50)]
  table2=[]
  for i in range(50):
      table2.append(f(i))
  tables=[table, table2]
  print (tabulate(tables))
  </code></pre>
  
  <p>When I run this code, it gives me a weird error. I looked up on the net some but they were all related to zero division. My problem occurs at numpy.cos when I used it before without "root" operation it worked fine. It also returns an error about tabulate as "'int' object is not iterable" which I really dont get it why?. Here is the error:</p>
  
  <pre><code>limit.py:5: RuntimeWarning: invalid value encountered in double_scalars
    return cos(x)**(1/3)
  Traceback (most recent call last):
    File "limit.py", line 12, in &lt;module&gt;
      print (tabulate(table, table2))
    File "/home/yav/anaconda3/lib/python3.6/site-packages/tabulate.py", line 1247, in tabulate
      tabular_data, headers, showindex=showindex)
    File "/home/yav/anaconda3/lib/python3.6/site-packages/tabulate.py", line 933, in _normalize_tabular_data
      rows = list(map(list,rows))
  TypeError: 'int' object is not iterable
  </code></pre>
  
  <p>I am just a beginner, so if you can explain more simpler, will be appreciated. Thank you very much</p>