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As i See in ML Course a VC dimension calculation is very theoretical.

What is the VC-dimension of intervals in R?

The target function is specifieed by an interval, and labels any example positive i it lies inside that interval.

Answers:

VC-dim = 2. A set of two points can be shattered, since there's only a single block of positive examples that could lie within the interval. But no set of 3 points can be shattered, because it can not be labeled in alternating +; - ; + order.

so i'm get stuck with meaning of interval.

for example, it means {(a, b) | "a is lower than b", a,b is real number} has VC-dim = 2?

Any idea or solution would be highly appreciated.

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Yes, an open interval in $\mathbb{R}$ is defined as $(a,b) = ]a,b[ = \left \{ x \in \mathbb{R}|\,a<x<b\right \} $. It has two parameters $a$ and $b$. The sets of all open intervals, i.e. $\left \{ \left \{ x \in \mathbb{R}|\,a<x<b\right \} | a,b \in \mathbb{R}\right\}$ has a VC dimension of 2 for the reason you mention. Keep in mind that the VC dimension of a hypothesis set $H$ is the most points $H$ can shatter.). To put it graphically:

enter image description here

(image from CalTech's free machine Learning online course by Yaser Abu-Mostafa Learning from Data)

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  • $\begingroup$ i confused !! yes or no :) Dear Richerby, be aware that a is lower than b, not lower equal than b ! $\endgroup$ – Ebraham Jun 17 '14 at 22:09
  • $\begingroup$ Thanks, I clarified the answer. Let me know If it's okay now. The strict inequality works too as you can take b arbitrarily close to a anyway. $\endgroup$ – Franck Dernoncourt Jun 17 '14 at 22:17
  • $\begingroup$ Dear Franck, some bracket insert wrongly in your anwers. can you put some detail to your answers? $\endgroup$ – Ebraham Jun 17 '14 at 22:18
  • $\begingroup$ @Ebraham Thanks for the feedback, which bracket insert is wrong and where are you stuck? $\endgroup$ – Franck Dernoncourt Jun 18 '14 at 0:58
  • $\begingroup$ no you correct it. just i want to find different between [-infinity <x <a, x is real number] with this example. i think this is a threshold and has a VC= 1. it's not interval ? yes? $\endgroup$ – Ebraham Jun 18 '14 at 5:48

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