title: How do take natural log of a double in MATLAB?
body: <p>I am attempting to that the natural log of a number, I get the message:</p>
  
  <pre><code>tf2 = 60*ln(B1);
  
  Undefined function 'ln' for input arguments of type 'double'.
  </code></pre>
  
  <p>So i try to cast the number as a float which the documentation claims it will accept but
  then i get the error message :</p>
  
  <pre><code>float(B1);
  
  Error using float (line 50)
  The input argument to float was not a supported type. The only recognized strings are     'single' and 'double'. The input type was 'double'
  </code></pre>
  
  <p>So then i try to cast the double as a single and get the same error but it says :</p>
  
  <pre><code>f=single(B1);
  float(B1);
  
  Error using float (line 50)
  The input argument to float was not a supported type. The only recognized strings are     'single' and 'double'. The input type was 'single'
  </code></pre>