# 1.2 Machine learning lecture 3  (Page 8/14)

That’s the [inaudible] but, yes. You are assuming that the error has zero mean. Which is, yeah, right. I think later this quarter we get to some of the other things, but for now just think of this as a mathematically – it’s actually not an unreasonable assumption. I guess, in machine learning all the assumptions we make are almost never true in the absence sense,right? Because, for instance, housing prices are priced to dollars and cents, so the error will be – errors in prices are not continued as value random variables, because houses can only be priced at a certain number of dollars and a certain number of cents and you never have fractions of cents in housing prices. Whereas a Gaussian random variable would. So in that sense, assumptions we make are never “absolutely true,” but for practical purposes this is a accurate enough assumption that it’ll be useful to make. Okay? I think in a week or two, we’ll actually come back to selected more about the assumptions we make and when they help our learning algorithms and when they hurt our learning algorithms. We’ll say a bit more about it when we talk about generative and discriminative learning algorithms, like, in a week or two. Okay?

So let’s point out one bit of notation, which is that when I wrote this down I actually wrote P of YI given XI and then semicolon theta and I’m going to use this notation when we are not thinking of theta as a random variable. So in statistics, though, sometimes it’s called the frequentist’s point of view, where you think of there as being some, sort of, true value of theta that’s out there that’s generating the data say, but we don’t know what theta is, but theta is not a random vehicle, right? So it’s not like there’s some random value of theta out there. It’s that theta is – there’s some true value of theta out there. It’s just that we don’t know what the true value of theta is. So if theta is not a random variable, then I’m going to avoid writing P of YI given XI comma theta, because this would mean that probably of YI conditioned on X and theta and you can only condition on random variables. So at this part of the class where we’re taking sort of frequentist’s viewpoint rather than the Dasian viewpoint, in this part of class we’re thinking of theta not as a random variable, but just as something we’re trying to estimate and use the semicolon notation. So the way to read this is this is the probability of YI given XI and parameterized by theta. Okay? So you read the semicolon as parameterized by. And in the same way here, I’ll say YI given XI parameterized by theta is distributed Gaussian with that.

All right. So we’re gonna make one more assumption. Let’s assume that the error terms are IID, okay? Which stands for Independently and Identically Distributed. So it’s going to assume that the error terms are independent of each other, right? The identically distributed part just means that I’m assuming the outcome for the same Gaussian distribution or the same variance, but the more important part of is this is that I’m assuming that the epsilon I’s are independent of each other. Now, let’s talk about how to fit a model. The probability of Y given X parameterized by theta – I’m actually going to give this another name. I’m going to write this down and we’ll call this the likelihood of theta as the probability of Y given X parameterized by theta. And so this is going to be the product over my training set like that. Which is, in turn, going to be a product of those Gaussian densities that I wrote down just now, right? Okay?

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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