Why doesn't the spreadsheet give the same result as those other "PageRank explanation sites" do?
|Very simple set-up|
|How to specify a very simple set-up|
Let's follow the calculations.
First we calculate Page1's PageRank. Page1 is pointed to from Page2, which points to two pages. So the formula becomes:
PR(Page1) = (1-d) + d (PR(Page2)/2) = (1 - 0.85) + 0.85 (1/2) = 0.575
So we turn our attention to Page2 - and our trouble starts. Page2 is pointed to from Page1 and Page3. But we have just calculated a new PageRank for Page1. So which one do we use in this calculation - the initial value or the new value? And when we calculate Page3's PageRank, do we use Page2's new PageRank?.
|First iteration, skewed method|
There are several things to be noted here:
- In the long run the values will converge and become the same.
- The "skewed" method will converge faster.
- With the "skewed" method Page1 and 3 have different ranks - even though they ought to be identical (they will be - after enough iterations).
- With the "skewed" method the site's total PageRank is not exactly 3 (it will be - after enough iterations).
So which method is used by Google? Nobody outside the Googleplex knows - and it doesn't matter since the values end up the same.
If you prefer, you can get a skewed spreadsheet instead.