title: trouble while running for code in Product Market introduction
body: <p>I 'm new here, and I am encountering a problem. I have taken an already existing code for 2 new products entering the market and I am trying to modify it to support 3 products. I have added all the extra variables and conditions needed but it shows an error on plotting. Could it be the excel or...? I could use some help on this...If any extra info is needed, I 'd be happy to provide you! Thanks for your time in advance!</p>
  
  <p>the error is:
  <a href="http://prntscr.com/9gy84l" rel="nofollow">http://prntscr.com/9gy84l</a></p>