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Okay. Any questions? Yeah?

Student: You are, I think here you try to measure the likelihood of your nice of theta by a fraction of error, but I think it’s that you measure because it depends on the family of theta too, for example. If you have a lot of parameters [inaudible] or fitting in?

Instructor (Andrew Ng) :Yeah, yeah. I mean, you’re asking about overfitting, whether this is a good model. I think let’s – the thing’s you’re mentioning are maybe deeper questions about learning algorithms that we’ll just come back to later, so don’t really want to get into that right now. Any more questions? Okay.

So this endows linear regression with a probabilistic interpretation. I’m actually going to use this probabil – use this, sort of, probabilistic interpretation in order to derive our next learning algorithm, which will be our first classification algorithm. Okay? So you’ll recall that I said that regression problems are where the variable Y that you’re trying to predict is continuous values. Now I’m actually gonna talk about our first classification problem, where the value Y you’re trying to predict will be discreet value. You can take on only a small number of discrete values and in this case I’ll talk about binding classification where Y takes on only two values, right? So you come up with classification problems if you’re trying to do, say, a medical diagnosis and try to decide based on some features that the patient has a disease or does not have a disease. Or if in the housing example, maybe you’re trying to decide will this house sell in the next six months or not and the answer is either yes or no. It’ll either be sold in the next six months or it won’t be. Other standing examples, if you want to build a spam filter. Is this e-mail spam or not? It’s yes or no. Or if you, you know, some of my colleagues sit in whether predicting whether a computer system will crash. So you have a learning algorithm to predict will this computing cluster crash over the next 24 hours? And, again, it’s a yes or no answer.

So there’s X, there’s Y. And in a classification problem Y takes on two values, zero and one. That’s it in binding the classification. So what can you do? Well, one thing you could do is take linear regression, as we’ve described it so far, and apply it to this problem, right? So you, you know, given this data set you can fit a straight line to it. Maybe you get that straight line, right? But this data set I’ve drawn, right? This is an amazingly easy classification problem. It’s pretty obvious to all of us that, right? The relationship between X and Y is – well, you just look at a value around here and it’s the right is one, it’s the left and Y is zero. So you apply linear regressions to this data set and you get a reasonable fit and you can then maybe take your linear regression hypothesis to this straight line and threshold it at 0.5. If you do that you’ll certainly get the right answer. You predict that if X is to the right of, sort of, the mid-point here then Y is one and then next to the left of that mid-point then Y is zero.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
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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