title: matlab adding a string to each element of a numeric vector
body: <p>I need to switch between a vector of numerics and a vector of strings:</p>
  
  <pre><code>a = [1, 2, 4, 5]
  b = {'xx1', 'xx2', 'xx3', 'xx4'}
  </code></pre>
  
  <p>I tried <code>strcat('XX', num2str(a))</code>, but it returns <code>XX1 2 3 4 5</code>, which is not what I want. Can someone tell me how to create <code>b</code> from <code>a</code> and how to create <code>a</code> from <code>b</code>? Thanks! </p>