I do not think that there is anything or will be anything called Yahoo Pagerank...Yahoo had a similar system to Pagerank called Yahoo WebRank a few years ago i.e. 2004, when Pagerank was still in its infancy. The system was similar to Google Pagerank and they used to rank website from 0 to 10. Later on, Yahoo closed the system. Digital point also had a Yahoo webrank checker, here is the link http://tools.digitalpoint.com/webrank.php
In my blog "Kangravision.blogspot.com" the robot.txt file is disallow....How I changed it to "allow"?
Yahoo is essential losing the market share. Thus to shoot for a high yahoo page rank isn't nearly as critical as high Google page rank.
Don't bother with Yahoo, optimize for google. It brings you much more traffic. Yahoo lost it's importance as a search engine many years ago.
Before anyoen cares about Yahoo PR then Yahoo must at least catch Google in SE battle otherwise why bother with Yahoo PR if Google PR is more important because more people use Google.
IF they did come up with a page rank and they had a different algorithm then you would need to choose one to follow, I know which one I would be following - for now anyway I would take any notice of it.
If yahoo rolls out something like a pagerank and its widely accepted by webmasters that will be quite good for business. Good old days of TLA will return