# 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.

#### Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Machine learning. OpenStax CNX. Oct 14, 2013 Download for free at http://cnx.org/content/col11500/1.4
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