title: error in using sqrt function for unit
body: <p>I am executing this code which contains the following line of code:  </p>
  
  <pre><code>sf_den=sqrt(sf_den+a*b);  
  </code></pre>
  
  <p>But I am getting the following error,I cannot figure out why  </p>
  
  <pre><code>Undefined function or method 'sqrt' for input arguments of type 'uint8'.
  </code></pre>
  
  <p>Value of a is 0 and b is &lt;171x210x3 uint8><br>
  What should i do?</p>