# 1.4 Machine learning lecture 5  (Page 11/15)

So say I get a piece of email, and what I’ll do is I’ll then scan through this list of words, and wherever a certain word appears in my email, I’ll put a 1 there. So if a particular email has the word “aid” then that’s 1. You know, my email doesn’t have the words ausworth or aardvark, so it gets zeros. And again, a piece of email, they want me to buy something, CS229 doesn’t occur, and so on, okay? So this would be one way of creating a feature vector to represent a piece of email.

Now, let’s throw the generative model out for this. Actually, let’s use this. In other words, I want to model PFX given Y. The given Y = 0 or Y = 1, all right? And my feature vectors are going to be 0, 1 to the N. It’s going to be these split vectors, binary value vectors. They’re N dimensional. Where N may be on the order of, say, 50,000, if you have 50,000 words in your dictionary, which is not atypical. So values from – I don’t know, mid-thousands to tens of thousands is very typical for problems like these.

And, therefore, there two to the 50,000 possible values for X, right? So two to 50,000 possible bit vectors of length 50,000, and so one way to model this is the multinomial distribution, but because there are two to the 50,000 possible values for X, I would need two to the 50,000, but maybe -1 parameters, right? Because you have this sum to 1, right? So -1. And this is clearly way too many parameters to model using the multinomial distribution over all two to 50,000 possibilities.

So in a Naive Bayes algorithm, we’re going to make a very strong assumption on PFX given Y, and, in particular, I’m going to assume – let me just say what it’s called; then I’ll write out what it means. I’m going to assume that the XI’s are conditionally independent given Y, okay?

Let me say what this means. So I have that PFX1, X2, up to X50,000, right, given the Y. By the key rule of probability, this is PFX1 given Y times PFX2 given Y, X1 times PF – I’ll just put dot, dot, dot. I’ll just write 1, 1 × dot, dot, dot up to, you know, well – whatever. You get the idea, up to PFX50,000, okay?

So this is the chain were of probability. This always holds. I’ve not made any assumption yet, and now, we’re gonna meet what’s called the Naive Bayes assumption, or this assumption that X defies a conditionally independent given Y. Going to assume that – well, nothing changes for the first term, but I’m gonna assume that PFX3 given Y, X1 is equal to PFX2 given the Y. I’m gonna assume that that term’s equal to PFX3 given the Y, and so on, up to PFX50,000 given Y, okay? Or just written more compactly, means assume that PFX1, PFX50,000 given Y is the product from I = 1 to 50,000 or PFXI given the Y, okay?

And stating informally what this means is that I’m, sort of, assuming that – so unless you know the cost label Y, so long as you know whether this is spam or not spam, then knowing whether the word “A” appears in email does not affect the probability of whether the word “Ausworth” appears in the email, all right?

#### Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
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
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele 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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 By By Mistry Bhavesh