title: MATLAB error: input argument undefined
body: <p>I've got a small MATLAB function I'm attempting to run by calling it from the command line, as follows:</p>
  
  <pre><code>&gt;&gt; [x, y , true_HF, max_F]=main (10)
  </code></pre>
  
  <p>However, when run, I end up with an error: </p>
  
  <pre><code>??? Input argument "HF" is undefined.
  </code></pre>
  
  <p>Searching online has yielded a bunch of results for people forgetting the argument, which I don't believe I'm doing (I'm a newb at this stuff).</p>
  
  <p>For reference, my "main" function:</p>
  
  <pre><code>function [ x, y, true_HF, max_F ] = main(HF)
      global Data
      Data = [];
      close all
      true_HF = fzero ( diff_L, HF );
      [x,y] = find_xy ( true_HF );
      final_graphs()
      max_F = max_force ( y, true_HF );
  end
  </code></pre>
  
  <p>Additionally, a "whos" prior to the offending line (That is, "true_HF = fzero ( diff_L, HF );"), shows that the variable HF is set.</p>
  
  <p>Any MATLAB geniuses out there who know what I'm doing wrong?</p>