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Okay so in the first course of this specialization,
we introduced this block diagram or flow chart for regression.
As well as a bunch of other machine learning tasks, but
I just want to walk through this again.
So we're going to assume that we have some training data.
Okay, so all of a sudden I've said the word training data,
and I hadn't said that to this point.
That's a topic we discussed at a very high level
in the first course of the specialization,
and we're gonna discuss the concepts of training data, test data, validation sets,
lots of other ideas about fitting our models and accessing our fits.
And chosing between models and all these different topics.
We're gonna discuss that in this course.
But for right now, if you don't know what it means to have training data, go back to
the first course of this specialization, watch that video or look it up online.
For now, I'm gonna assume that you know that we've some training data and
we're using our training data to fit a specific model.
And for the rest of this module, that's gonna suffice,
we're only looking at training data.
And all the other discussion about validation sets, test sets,
and everything like this, choosing between models,
assessing the fit of the models, that's going to come later in this course.
Okay, so when I talk about data in the rest of this module,
I'm assuming we're talking about just our training set,
that we've already done some split and we have our training data, okay.
Think I've said enough on that.
So, we have our training data and in this case,
that's gonna be some table of house id,
house square feet and then the house sales price.
And we have this big table of all these quantities.
And then what we're going to do, is extract some features.
So maybe, actually, at this point instead of specifically saying how square feet,
I can just say that there's some set of house attributes.
We might have things in addition to square feet.
And so one step we're gonna have to do is figure out what input we're gonna use for
our regression model.
We're gonna talk about more general features later in the course, but for
now we're just assuming a simple setup where we're gonna choose one of our house
attributes, call that the input to this regression model, and work from there.
So, we've talked about using square feet as our selected input
and then we're gonna use our Machine Learning model,
which is regression, to predict our house sales prices.
So y hat represents our predicted,
house sales price.
And how are we predicting it?
Well, based on some estimated line or curve,
so this is our, f hat is our estimated function.
That's fit from our data set, or, specifically our training data set.
And how are we gonna determine f hat?
Or how are we gonna estimate this function?
Well, first we're gonna need to describe some quality metric that says
I should describe what Y is.
I already mentioned this earlier, but let's write it down explicitly.
This is the sales price, the actual
sales price of our houses, and we're gonna compare the actual
sales price to the predicted sales price using the any given F hat.
We're gonna say how well did we do?
And that's what the quality metric is.
So there's gonna be some error in our predicted values.
And the machine learning algorithm we're gonna use to fit these
regression models is gonna try to minimize that error.
So it's gonna search over all these functions to reduce the error
in these predicted values.
Okay, so this is our overall flow chart and
we're gonna walk through the various components of this throughout this
module and in more depth in the rest of this course.
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