title: What is R squared for a neural network and what does it signify?
body: <p>I calculated R square for my neural network based on a formula I found somewhere, which goes something like:</p>
  
  <p><img src="https://i.stack.imgur.com/DojZC.png" alt="enter image description here"></p>
  
  <p>It should be something around 0.98-0.99. But, when I operate it on my network, it yields very low values, sometimes even negative. What can be the reason for this? What does R square signify?</p>