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equally interesting question might be
how we figured out
what is the first word that comes to mind for example
what's the first four starting with anne
many of you might say apple
i some words more important than others
is adjusted common words which are more important than others
in this context if you're talking about
discourse in this lecture
what's the first word that comes to mind
starting with g_
i'd bet many of you think
does this
have anything to withhold google figures out
which topics to include
ended up ten documents
displays matching the query clinton plays in getprice
importance
search results can google
as many of you may have read
is because of an algorithm called pagerank likud described in a minute
but we also want to ask is there anything deeper
which will come to just
after that
so let's look at page here
the web consists of documents which are linked to each other
through hyperlinks
and this was the initial structure of the web
when the first became very popular in the late nineties
and uh... remains so today but we'll come two-bit come to that uh... shortly
as to how it might be changing
so what uh... brilliant bache at uh... google wistful the founders of google
imagined
by the most of the stanford
uh... was
suppose there's a random sex
who hops from page two page hyperlink to hyperlink
contract
so at a page the suffrage uses at random penny of the links
that kal out from that page
so the servers going from page two page
and the question that
sergey brin and larry page fast ones
what is the relative probability of visiting a particular so
of all the pages on the web
which pages are more likely to be visited by such a random suffer
than others
and that probably the across all the pages on the web
is a pager ankle that ***
it might be a
that the number of hyperlinks
going into a page
is sufficient to computers patriot
obviously
if more links point to a page
more likely it is that this random self-rule reach them
question is
is this enough
he turns out
that this is not
and the answer is no because
even this a page doesn't have
many incoming links
a sofa and revisited bs
because of cycles in the graph
so that
the central goal of and come back to the base through a variety of different
routes
any jurors in the same link
again and again
but because there are so many cycles sweet return
back
to the same page
a particular page could become important
even if it doesn't have a lot of incoming hyperlinks
the point is that page rankings that global property
of this web graph
and
cannot be computed
simply by looking at the number of links of each page
this is the second major competition did a search engine like google has to do
computing the page rank the each page
the first of course being indexing the web as it grows
this page rank of each page is computed interactively
continuously
entitle
on as we shall see
thousands and thousands of service
for those of you who are slightly more mathematically minded
but they drank is related to
the eigen vector of a particular jcc matrix
but we're not going to go into that math
in this course