title: Magento - Calculated Product Attribute (property)
body: <p>I would like to add a calculated attribute (property) to Products. It's value is to be calculated using a PHP function eg:</p>
  
  <pre><code>function CalculateCustomAttribute() {
    ...
    //Do some calculations based on other Product attributes, date, etc 
    ...
    return $calculatedValue; // type float
  }
  </code></pre>
  
  <p>This calculated attribute needs to be:</p>
  
  <ul>
  <li>displayed in the Product page,</li>
  <li>filterable through the "Layered Navigation", and</li>
  <li>sortable in the "Product Listing".</li>
  </ul>
  
  <p>Could this be done? And how?</p>