afl-material: comparison videos/02-algo2.srt

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-:3a12e096f9a0
+:3bf3f5bb067e
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-They come back after
+Welcome back. After
 this disappointment
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-and case of over promising
+and case of over-promising
-and under achieving.
+and under-achieving,
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-Let's have a look whether
+let's have a look whether
 we can recover from that.
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 So here's one problem.
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-Then we looked at this end
+When we looked at this
-times vk expression and
+n-times regular expression, we
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-be able to represent
+were not able to represent
 that directly.
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-We had two represented as a
+We had to represent it as a
-sequence record expression.
+sequence regular expression.
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 So we expanded it.
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-So times one would be just a,
+So times-one would be just a,
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-t, times two would
+times-two would
-be a, and so on.
+be a o a, and so on.
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 And so you can see if
 you go already to 13,
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-N equals 13, the record
+n equals 13, the regular
 expression becomes quite large.
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 And now the functions
-nullable and also derivative.
+nullable and also derivative,
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-They need to traverse
+they need to traverse
-this reg expression.
+this regular expression.
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-Remember this tree in sometimes
+Remember this tree, sometimes,
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 they have to traverse
 that even several times.
 down the algorithm.
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 And in particular, because
-our first reg expression was
+our first regular expression was
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-actually not just a bot
+actually not just a, but
-a plus one. So b hat.
+a + 1. So we had
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-In the case of 13,
+in the case of 13,
-we had a plus one,
+we had a + 1, a + 1,...
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-a plus one a plus born 13 times.
+a + 1... 13 times.
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-And this reg
+And this regular
-expression just grows,
+expression just grows
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-stay in number n. Just to
+with the number n. Just to
-show you this also encode,
+show you this also in code,
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-I'm Stern, This File rewarm
+I'm in the file re1.sc,
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-and D and I have a size function.
+and in the end I have a size function.
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 The size function takes
 a regular expression as
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-argument and produces in teacher.
+argument and produces an integer.
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 And essentially it takes
-this rec expression scene as
+this regular expression, seen as
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-a tree and count how many
+a tree and counts how many
-nodes are in this tree.
+nodes there are in this tree.
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-And so if I take this even
+And so if I take this EVIL1
-one reg expression, this one,
+regular expression, this one,
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 and increase now this n. So you
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 can already see
-for any cross one,
+for n = 1,
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 the size of this
-record expression is
+record expression is 5
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-five and you see it
+and you see it
 slowly increases.
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-And this 20 n equals 20.
+And this 20, i.e. n = 20,
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-The size of this record
+the size of this regular
-expression is SMOW already a 119.
+expression is now already 119.
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-So now the interesting
+The interesting
-line as this one.
+line is this one.
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-Remember it when we
+Remember, when we
 built the derivative,
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-very often parts of a reg
+very often parts of a regular
 expression gets copied.
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-So if you have like EVA,
+So if you have like EVIL1
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-one of 2019 nodes,
+of 20, and you have 119 nodes,
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 now this will be often copied.
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 And we want to see what's the
-resulting tree look like,
+resulting tree look like, i.e.
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-how many nodes it has.
+how many nodes does it have.
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-So I take here either one of 20
+So I take here EVIL1 of 20
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 and the derivative
 according to 20 a's.
 And just have a look
 what the size is.
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-Okay, that takes away.
+Okay, that takes a while.
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-You see now this rec expression,
+You see now this recular expression,
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 the derivative has already
 8 million plus nodes.
 derivative have to
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 traverse these trees with
-a million plus nodes.
+8 million plus nodes.
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 So it's no wonder
 that this is slow.
 00:03:03,860 --> 00:03:06,350
 this explosion problem is to
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-have an explicit and
+have an explicit
-times reg expression.
+n-times regular expression.
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 So instead of expanding
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 it to the sequence
-reg expression,
+regular expression,
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 let's just have a single
-wreck expression and times,
+regular expression n-times,
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 which takes an expression and
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-a number and keeps that
+a number, and keeps that
-regular expression Small.
+regular expression small.
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-I'm here in the fire V2,
+I'm here in the file re2.sc,
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-which is also on Keats.
+which is also on KEATS.
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 And the only change I made
 is I added explicitly
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-a wrecker expression for
+a regular expression for
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-N times the optional
+n-times. The optional
-reg expression.
+regular expression
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-Very leaf out at the
+we leave out at the
-moment because this a
+moment because this a?
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-optional is represented as
+is represented as
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-a plus one and doesn't
+a + 1 and doesn't
-explain too much.
+expand too much.
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-The really the culprit
+The real culprit
-is this n times.
+is this n-times.
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 And instead of expanding
-it n times, which has,
+it n-times, we just
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-take here a wreck expression
+take here a regular expression
 and a natural number,
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 which says how many times
 can keep it small.
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 But by adding that
-reg expression,
+regular expression,
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 we now have to think about
 cases for nullable and
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-derivative so that we have
+derivative. So that we have
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-to now calculate next
+to calculate next
 what they look like.
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 00:04:10,205 --> 00:04:14,060
 We can actually
 Remember, if you have
 a regular expression,
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-R and B take in
+r and we take it
-times of this are,
+n-times of this r,
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-then indicates if n equals 0,
+then in case if n = 0,
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-we find that as the
+we definded that as the
-one reg expression.
+1 regular expression.
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-If n equals one,
+If n = 1,
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 it will be just a
-single copy of on.
+single copy of r.
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-If n equals two,
+If n = 2,
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-it will be two copies.
+it will be two copies in sequence.
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-Sequence if three, we have
+If three, we have
 three copies and so on.
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 Now we have to
 somehow characterize
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-when these cases all nullable.
+when are these cases all nullable.
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 Well, if n equals 0,
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-then this will be defined as one,
+then this will be defined as 1.
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-so one can match
+So 1 can match
 the empty string.
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 So that should be
 definitely true.
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-Okay, if any cross one,
+Okay, if n = 1,
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-when can this reg expression
+when can this regular expression
 match the empty string?
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-So vent should be nullable.
+So when should this be nullable?
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-Well, if nullable of our holes,
+Well, if nullable of r holds,
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-okay, so if I can match
+If it can match
 the empty string,
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 then we can match
 When can this regular expression
 match the empty string?
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-So these are now two copies of
+So these are now two copies of r.
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-our well-posed copies need
+Well, both copies need
 to match the empty string.
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 So again, we have to ask
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 both of them need to be nullable.
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-Ok? Similarly, in the third case,
+Similarly, in the third case,
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 all three copies need to be
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 able to match the empty
-string. Men, is that the case?
+string. When is that the case?
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 Well, if nullable of
-our holes and so on.
+r holds and so on.
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 So we can actually define that
-if n equals 0, then true.
+if n = 0, then true,
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-Else we have to ask with
+else we have to ask whether
-nullable of our holes.
+nullable of r holds.
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 So that will be the clause we
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 have to implement for
-n times and nullable.
+n-times and nullable.
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 Deriving the definition for
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-the derivative of the n terms
+the derivative of the n-times
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-reg expression.
+regular expression
-It's not that easy.
+is not that easy.
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-So we have to look again
+We have to look again
 how it was defined
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 earlier and we somehow
 have to spot a pattern.
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-The voice, our
+Otherwise, our
 algorithm will be again
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-quite slow if you don't
+quite slow if we don't
 spot that pattern.
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 So let's have a look.
 So in the case that
 n is equal to 0,
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-then r n times most
+then r n-times was
-defined as just one.
+defined as just 1.
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 What would be the
 derivative of one?

changeset 772	3bf3f5bb067e
parent 769	f9686b22db7e
child 773	260e330f7466