# 1.15 Machine learning lecture 16  (Page 12/15)

So I should write down some other things first, just to ground the notations, but what I’ll do is eventually come up with an algorithm for computing V*, the optimal value function and then we’ll plug them into this and that will give us the optimal policy p*.

And so I’ll write down the algorithm in a second, but just to ground the notation, well – yeah, let’s skip that. Let’s just talk about the algorithm. So this is an algorithm called value iteration and it makes use of Bellman’s equations for the optimal policy to compute V*. So here’s the algorithm. Okay, and that’s the entirety of the algorithm and oh, you repeat the step, I guess. You repeatedly do this step.

So just to be concrete, let’s say in my MDP of 11 states, the first step is initialize V(s) equals zero, so what that means is I create an array in computer implementation, create an array of 11 elements and say set all of them to zero. Says I can initialize into anything. It doesn’t really matter.

And now what I’m going to do is I’ll take Bellman’s equations and we’ll keep on taking the right hand side of Bellman’s equations and overwriting and start copying down the left hand side. So we’ll essentially iteratively try to make Bellman’s equations hold true for the numbers V(s) that are stored along the way. So V(s) here is in the array of 11 elements and I’m going to repeatedly compute the right hand side and copy that onto V(s).

And it turns out that when you do this, this will make V(s) converge to V*(s), so it may be of no surprise because we know V* [inaudible] set inside Bellman’s equations.

Just to tell you, some of these ideas that they get more than the problem says, so I won’t prove the conversions of this algorithm. Some implementation details, it turns out there’s two ways you can do this update. One is when I say for every state s that has performed this update, one way you can do this is for every state s, you can compute the right hand side and then you can simultaneously overwrite the left hand side for every state s. And so if you do that, that’s called a sequence update. Right and sequence [inaudible], so update all the states s simultaneously.

And if you do that, it’s sometimes written as follows. If you do synchronous update, then it’s as if you have some value function, you’re at the Ith iteration or Tth iteration of the algorithm and then you’re going to compute some function of your entire value function, and then you get to set your value function to your new version, so simultaneously update all 11 values in your s space value function.

So it’s sometimes written like this. My B here is called the Bellman backup operator, so the synchronized valuation you sort of take the value function, you apply the Bellman backup operator to it and then the Bellman backup operator just means computing the right hand side of this for all the states and you’ve overwritten your entire value function.

The only way of performing these updates is asynchronous updates, which is where you update the states one at a time. So you go through the states in some fixed order, so would update V(s) for state No. 1 and then I would like to update V(s) for state No. 2, then state No. 3, and so on. And when I’m updating V(s) for state No. 5, if V(s) prime, if I end up using the values for states 1, 2, 3, and 4 on the right hand side, then I’d use my recently updated values on the right hand side. So as you update sequentially, when you’re updating in the fifth state, you’d be using values, new values, for states 1, 2, 3, and 4. And that’s called an asynchronous update.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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