title: Propagation in Python - Pandas Series TypeError
body: <p>I am trying to propagate uncertainty in Python by adding two columns together of a Pandas data frame and then taking the square root. However, when I try to use Python's <code>math.sqrt</code> function, I receive a <code>TypeError: cannot convert the series to &lt;class 'float'&gt;</code>.</p>
  <p>Here is what I've been doing:</p>
  <pre><code>joinedDF['combined_error'] = math.sqrt((joinedDF.error1**2 + joinedDF.error2**2).astype(float))
  </code></pre>
  <p>Using <code>joinedDF.dtypes</code>, I've verified that both error columns are <code>float64</code>.</p>
  <p>I've even tried seperating everything out, but I still receive a TypeError. Any suggestions about how to mend this?</p>