title: Converting a string to an expression in MATLAB
body: <p>I'm writing a small MATLAB package and I'd like to ask for user input for a function. So if the user enters:</p>
  
  <pre><code>x.^2 + sin(x)
  </code></pre>
  
  <p>I want to use this user input to appear elsewhere in the code, but <code>x</code> would already be defined and so the expression above would be a vector (or scalar if <code>length(x)</code> is 1).</p>