DVD - Lecture 7b: Random Placement

[@haziqiqbalhussain]

Thanks for the amazing lectures, sir. I have a question. At 5:00 the HPWL calculated is 7 while if we count the units manually it's 9 as each of the two bottom right cells are also taking one unit of wirelength. You said that these cell doesn't add much in the wirelength but what if they are a little far (inside the bounding box). The actual wirelength can be 10 or 11 units and our estimation would be quite off.

[@AdiTeman]

Hi Haziq, Your question is legitimate, because I can say that I have been confused by this more than once (don't tell anyone 😂). But actually, it's almost irrelevant. The reason is that we are building an estimator that is trying to somehow quantify the wirelength, so we can define a cost function and optimize it. It is very clear that our estimator is far from accurate - it just needs to represent something that is better or worse than something else, so we can change it and see if that helps. So counting the distance (|x1-x2|) or the number of blocks that the wire occupies (which comes out |x1-x2|+1) is essentially the same for the purpose we are using it. In addition to that, as you will see in the following parts of the lecture, we are actually using other estimators more predominantly (such as the quadratic wirelength estimator). But the point is the same - we are trying to put a number that represents how good or bad our solution is for comparison to a different solution. You could look at it as a rating system that gives you 1-5 stars or a grade of 1-10 - as long as the better option has a higher rating, it doesn't really matter what the scale is.

[@haziqiqbalhussain]

@@AdiTeman Thanks. I have completed the following parts of the lecture and got your point. Thank you for taking your time out and explaining.

[@AdiTeman]

@@haziqiqbalhussain Great

[@tcwu2005]

Very clear !

[@AdiTeman]

Glad you think so!