# 1.2 Machine learning lecture 3  (Page 7/14)

Actually, just quickly raise your hand if you’ve seen a Gaussian distribution before. Okay, cool. Most of you. Great. Almost everyone. So, in other words, the density for Gaussian is what you’ve seen before. The density for epsilon I would be one over root 2 pi sigma, E to the negative, epsilon I squared over 2 sigma squared, right? And the density of our epsilon I will be this bell-shaped curve with one standard deviation being a, sort of, sigma. Okay? This is form for that bell-shaped curve. So, let’s see. I can erase that. Can I erase the board? So this implies that the probability distribution of a price of a house given in si and the parameters theta, that this is going to be Gaussian with that density. Okay? In other words, saying goes as that the price of a house given the features of the house and my parameters theta, this is going to be a random variable that’s distributed Gaussian with mean theta transpose XI and variance sigma squared. Right? Because we imagine that the way the housing prices are generated is that the price of a house is equal to theta transpose XI and then plus some random Gaussian noise with variance sigma squared. So the price of a house is going to have mean theta transpose XI, again, and sigma squared, right? Does this make sense? Raise your hand if this makes sense. Yeah, okay. Lots of you.

In point of notation – oh, yes?

Student: Assuming we don’t know anything about the error, why do you assume here the error is a Gaussian?

Instructor (Andrew Ng) :Right. So, boy. Why do I see the error as Gaussian? Two reasons, right? One is that it turns out to be mathematically convenient to do so and the other is, I don’t know, I can also mumble about justifications, such as things to the central limit theorem. It turns out that if you, for the vast majority of problems, if you apply a linear regression model like this and try to measure the distribution of the errors, not all the time, but very often you find that the errors really are Gaussian. That this Gaussian model is a good assumption for the error in regression problems like these. Some of you may have heard of the central limit theorem, which says that the sum of many independent random variables will tend towards a Gaussian. So if the error is caused by many effects, like the mood of the seller, the mood of the buyer, some other features that we miss, whether the place has a garden or not, and if all of these effects are independent, then by the central limit theorem you might be inclined to believe that the sum of all these effects will be approximately Gaussian. If in practice, I guess, the two real answers are that, 1.) In practice this is actually a reasonably accurate assumption, and 2.) Is it turns out to be mathematically convenient to do so. Okay? Yeah?

Student: It seems like we’re saying if we assume that area around model has zero mean, then the area is centered around our model. Which it seems almost like we’re trying to assume what we’re trying to prove. Instructor?

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
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?
what is a peer
What is meant by 'nano scale'?
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
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
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?
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
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