title: Make knockout listen to values changes which are not a result of a keystroke
body: <pre><code>self.totalHours = ko.pureComputed(function() {
          var start=self.num1;
          var end=self.num2;
          return start+end; 
  });
  
  &lt;input   type="text" data-bind="textInput: start"&gt;
  &lt;input  type="text" data-bind="textInput: end"&gt;
  &lt;input  type="text" data-bind='text: totalHours()'&gt;
  </code></pre>
  
  <p>The above first is part of my <code>viewmodel</code> and the second is part of my <code>model</code>. num1,num2 are <strong>observables</strong>. Every time I change <strong>manually</strong> the value inside the above first two inputs the third input is updated immediately; however, when the values change <strong>by code</strong>, knockout does not listen to the changes and <code>total</code> is not updated. How may I oblige knockout to listen to the changes provoked by code?</p>