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And so having estimated all these parameters, when you’re given a new piece of email that you want to classify, you can then compute PFY given X using Bayes rule, right? Same as before because together these parameters gives you a model for PFX given Y and for PFY, and by using Bayes rule, given these two terms, you can compute PFX given Y, and there’s your spam classifier, okay? Turns out we need one more elaboration to this idea, but let me check if there are questions about this so far.

Student: So does this model depend on the number of inputs?

Instructor (Andrew Ng) :What do you mean, number of inputs, the number of features?

Student: No, number of samples.

Instructor (Andrew Ng) :Well, N is the number of training examples, so this given M training examples, this is the formula for the maximum likelihood estimate of the parameters, right? So other questions, does it make sense? Or M is the number of training examples, so when you have M training examples, you plug them into this formula, and that’s how you compute the maximum likelihood estimates.

Student: Is training examples you mean M is the number of emails?

Instructor (Andrew Ng) :Yeah, right. So, right. So it’s, kind of, your training set. I would go through all the email I’ve gotten in the last two months and label them as spam or not spam, and so you have – I don’t know, like, a few hundred emails labeled as spam or not spam, and that will comprise your training sets for X1 and Y1 through XM, YM, where X is one of those vectors representing which words appeared in the email and Y is 0, 1 depending on whether they equal spam or not spam, okay?

Student: So you are saying that this model depends on the number of examples, but the last model doesn’t depend on the models, but your phi is the same for either one.

Instructor (Andrew Ng) :They’re different things, right? There’s the model which is – the modeling assumptions aren’t made very well. I’m assuming that – I’m making the Naive Bayes assumption. So the probabilistic model is an assumption on the joint distribution of X and Y. That’s what the model is, and then I’m given a fixed number of training examples. I’m given M training examples, and then it’s, like, after I’m given the training sets, I’ll then go in to write the maximum likelihood estimate of the parameters, right? So that’s, sort of, maybe we should take that offline for – yeah, ask a question?

Student: Then how would you do this, like, if this [inaudible] didn’t work?

Instructor (Andrew Ng) :Say that again.

Student: How would you do it, say, like the 50,000 words –

Instructor (Andrew Ng) :Oh, okay. How to do this with the 50,000 words, yeah. So it turns out this is, sort of, a very practical question, really. How do I count this list of words? One common way to do this is to actually find some way to count a list of words, like go through all your emails, go through all the – in practice, one common way to count a list of words is to just take all the words that appear in your training set.

That’s one fairly common way to do it, or if that turns out to be too many words, you can take all words that appear at least three times in your training set. So words that you didn’t even see three times in the emails you got in the last two months, you discard. So those are – I was talking about going through a dictionary, which is a nice way of thinking about it, but in practice, you might go through your training set and then just take the union of all the words that appear in it.

Questions & Answers

Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
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.
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali 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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