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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

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
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
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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
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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