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Question:

What does the semicolon mean in "$(x(i), y(i)); i=1,\dots,m$"?

My Guess

"This is training example $(x_1, y_1)$ and it is in a set where $i$ is in the range $1$ to $m$".

Explanation:

I'm taking Andrew Ng's Machine Learning course on Coursera. He often uses math notation without explaining it.

This page has the paragraph ...

To establish notation for future use, we’ll use $x^{(i)}x (i)$ to denote the “input” variables (living area in this example), also called input features, and $y^{(i)}y (i)$ to denote the “output” or target variable that we are trying to predict (price). A pair $(x^{(i)}, y^{(i)})(x(i), y(i))$ is called a training example, and the dataset that we’ll be using to learn—a list of m training examples $(x(i),y(i));i=1,\dots,m$ — is called a training set. Note that the superscript “$(i)$” in the notation is simply an index into the training set, and has nothing to do with exponentiation. We will also use $X$ to denote the space of input values, and $Y$ to denote the space of output values. In this example, $X = Y = \mathbb{R}$.

This is a link to a screen shot of the above text. It's easier to read

Axle Max
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    In context it appears to mean "for $i=1$ to $i=m$". Thus it imagines that you are given $m$ data points, labeled as indicated. – lulu Sep 01 '18 at 17:24
  • wow! That was fast! So I was roughly right then. That doesn't happen often. Thank you for the rapid feedback. :-) – Axle Max Sep 01 '18 at 17:26
  • PS - I am guessing from your answer that semicolon doesn't have a clearly defined and common meaning then? – Axle Max Sep 01 '18 at 17:28
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    Context makes it perfectly clear, but I wouldn't have said it was entirely standard. – lulu Sep 01 '18 at 17:30
  • I am such a NooB! This is an enormous help. I am about to start a masters in AI and have been studying math for 3 months to get ready. This help may literally change my life. It means a lot. – Axle Max Sep 01 '18 at 17:57
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    Some (free) advice then: stay flexible. People write informally. Just how it is. It's not worth locking down every stray bit of the language. That inevitably means that a lot of things are phrased ambiguously. Doesn't mean it's wrong, exactly. Just means you need to be alert. Good luck! – lulu Sep 01 '18 at 18:13
  • Yeah. Ok. Thank you for the advice. Being honest it makes math and AI/ML seem inaccessible / snobby. I’m OK with it and thank God for Stackexchange but I want as many people as possible to learn and this will limit adoption which is sad. – Axle Max Sep 01 '18 at 18:57
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    I hear you. But, having been through it myself (more years ago than I choose to admit), I can assure you that it wouldn't help to formalize the language. The problem is that there is too much of it. Too many situations, too many ways to talk about things. Frustrating as it is, it is better to tolerate some ambiguity. Stick with it! Ask questions! We are always here to help, to the extent we can. – lulu Sep 01 '18 at 19:07
  • Thank you. It's very kind of you to help me and give good advice. I really appreciate it. :-) – Axle Max Sep 01 '18 at 19:29

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