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11:02 PM
@MikeMiller - Are you able to solve this? math.stackexchange.com/questions/1253004/…
 
11:18 PM
Hello everyone! Is here someone that knows Kruskal's algorithm?
My question is this:
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Q: The output spanning tree of Kruskal's algorithm is a minimum spanning tree

user159870I want to show that the output spanning tree $S$ of Kruskal's algorithm is a minimum spanning tree, so it is of minimum weight, by contradiction. We suppose that $S$ is not a minimum spanning tree. Let $T$ be a spanning tree which has the minimum weight. How can I go on to get a contradicti...

 
Here's a video on kruskal's: youtube.com/watch?v=71UQH7Pr9kU. It might be more basic than you need though.
 
11:36 PM
It doesn't show the correctness. Just an example. @Jeff
 
Right. I read your question after posting the video.
If K's algo did not find the minimum tree, then it must have selected an edge that wasn't the minimum at some point. @user159870
 
Hi @Jeff
Could I ask you something about the time complexity of an algorithm?
 
@evinda You can ask. But I haven't any more experience in that area than I do in K's algorithm. :D
 
0
Q: Time Complexity of modified dfs algorithm

evindaI want to write an algorithm that finds an optimal vertex cover of a tree in linear time O(n), where n is the number of the vertices of the tree. A vertex cover of a graph G=(V,E) is a subset W of V such that for every edge (a,b) in E, a is in W or b is in W. In a vertex cover we need to have ...

Do anyone knows if there is a tighter bound for the modifies dfs algorithm?
 
How are you people posting question snips?
 
11:45 PM
You post only the question
 
@evinda Way over my head, ev
 
Ok
 
@evinda How does one "post only the question"?
 
You put the link and send it
 
5
Q: Where does the proof of $\sqrt 2$ is irrational break down when trying to prove the same for $\sqrt 4$?

JeffI'm trying find where the common proof by contradiction that $\sqrt 2$ is irrational breaks down when trying to prove $\sqrt 4$ is irrational. Assume $(\frac pq)^2=4$ and $\gcd(p,q)=1$. I guess I could just let $p=2, q=1$ and be done, but why is that an adequate failure of the proof? If it's not...

oh. it does it automatically
 
11:48 PM
We suppose that S, the output spanning tree of Kruskal's algorithm, is not a minimum spanning tree.

Let $T$ be a spanning tree which has the minimum weight.

That means that $S$ contains an edge that wasn't the minimum at some point and $T$ contains the minimum one.

Correct so far? How can I go on? @Jeff
 
@user159870 First, I hope you didn't think I knew the answer. I'm guessing. I learned about K's algorithm a few minutes ago when I watched the video I posted. :D
@user159870 Second, I think that's already a contradiction. I mean, we know K's algo always selects the smallest weighted edge.
 
I don't think so. That is what we have supposed, that there is an other spanning tree with the smallest weight. We have to find something that cannot be true to conclude that our assumption, that $S$ is not a minimum spanning tree, is false. But I don't know how. @Jeff
 

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