Yes, I did mean that question. What about n=4 (I can't actually remember if this works or not)?(Original post by Llewellyn)
Are you sure this is the question you intended to ask? I remember a (very good) similar case where you were placing n black and n white queens on an infinite board such that no black piece can take a white piece and vice versa. Did you mean to ask this?
Otherwise I'm just getting n=3, simply by the fact that one queen must be the furthest left and the furthest down, thereby meaning it can at most interact with 3 other pieces (right, right/up diagonal and up). Unless I'm misreading this at 5am
For your question, it should work for all n. You can place queens far enough apart so that they do not attack any other queen. (this probably isn't the question you were thinking of though, any chance you could share that problem?)
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 31052015 11:26
Last edited by Renzhi10122; 31052015 at 13:15. 
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 31052015 18:18
(Original post by Renzhi10122)
Yes, I did mean that question. What about n=4 (I can't actually remember if this works or not)?
For your question, it should work for all n. You can place queens far enough apart so that they do not attack any other queen. (this probably isn't the question you were thinking of though, any chance you could share that problem?)
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I'll ask my brother because I'm pretty sure he originally showed me the question. The point is that you have an m by m square board, and you place n black queens and n white queens such that no black or white can attack each other. You then find the maximum 'density' (2n/m) that can be achieved.
So a trivial solution to the above would be to place opposite coloured queens a knight's move away from each other. However this is not optimal. 
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 31052015 19:05
(Original post by Llewellyn)
Yes, it occured to me that n=4 works for all boards larger than 3x3, that was stupid on my part
I'll ask my brother because I'm pretty sure he originally showed me the question. The point is that you have an m by m square board, and you place n black queens and n white queens such that no black or white can attack each other. You then find the maximum 'density' (2n/m) that can be achieved.
So a trivial solution to the above would be to place opposite coloured queens a knight's move away from each other. However this is not optimal. 
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 02062015 18:51
(Original post by Llewellyn)
Yes, it occured to me that n=4 works for all boards larger than 3x3, that was stupid on my part
I'll ask my brother because I'm pretty sure he originally showed me the question. The point is that you have an m by m square board, and you place n black queens and n white queens such that no black or white can attack each other. You then find the maximum 'density' (2n/m) that can be achieved.
So a trivial solution to the above would be to place opposite coloured queens a knight's move away from each other. However this is not optimal.
There is a reasonable variation on the same theme that gives 2/9. Improving this seems pretty hard (for me)Last edited by TheMagicMan; 02062015 at 18:58. 
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 02062015 20:02
(Original post by TheMagicMan)
The 'knight's solution has density 1/8 correct? (I'm not entirely sure what you mean)
There is a reasonable variation on the same theme that gives 2/9. Improving this seems pretty hard (for me)
I have got 1/4 so far, but I think I remember the limit being larger. I will check back when I don't still have exams 
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 02062015 20:33
(Original post by Llewellyn)
Yes, a lattice of points with (4x, 2y) black and (4x+2, 2y+1) white is 1/8. This is just an example of a solution, it's probably misleading to start from here.
I have got 1/4 so far, but I think I remember the limit being larger. I will check back when I don't still have exams
..X
XX
X
although I doubt you could get much better than 0.3 like that.
One way you could find a decent bound is to find a good solution for some m and then scaling up that solution. For example in the normal chessboard case 18 (n=9) is possible giving a density of ~0.28 so the optimal asymptotic density must be better than that.
The real challenge will be to find a good upper bound. I suspect 0.4 is easily an upper bound...any idea how to show that?
It would be nice to find some literature on this problem as I suspect it is somewhat beyond us. Any idea what the problem is called/ if it has a name?Last edited by TheMagicMan; 02062015 at 20:48. 
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 02062015 23:36
(Original post by TheMagicMan)
If you iterate my method (which is essenitally to put in blocks of queens of the same colour with the blocks relating to each other in a knight like way) it can be improved to 16/63 in the limit, although that is barely more than 1/4. I think there are efficiencies that can be made by by reducing the diagonal footprint of each block i.e. to make a block look like
..X
XX
X
although I doubt you could get much better than 0.3 like that.
One way you could find a decent bound is to find a good solution for some m and then scaling up that solution. For example in the normal chessboard case 18 (n=9) is possible giving a density of ~0.28 so the optimal asymptotic density must be better than that.
The real challenge will be to find a good upper bound. I suspect 0.4 is easily an upper bound...any idea how to show that?
It would be nice to find some literature on this problem as I suspect it is somewhat beyond us. Any idea what the problem is called/ if it has a name?
Searching is difficult because "chess problem" usually doesn't refer to maths, and the most common queen maths problem is just placing same coloured queens so they don't attack or placing knights of opposite colours.
I did find this: https://books.google.co.uk/books?id=...queens&f=false Which is also here http://ipg.host.cs.standrews.ac.uk/papers/spgW9.pdf
Which looks more promising than it likely is, they only run up to 12x12Last edited by Llewellyn; 02062015 at 23:37. 
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 03062015 19:45
(Original post by Llewellyn)
I feel like it is 3/7 (the upper bound). 1/2 also perhaps.
Searching is difficult because "chess problem" usually doesn't refer to maths, and the most common queen maths problem is just placing same coloured queens so they don't attack or placing knights of opposite colours.
I did find this: https://books.google.co.uk/books?id=...queens&f=false Which is also here http://ipg.host.cs.standrews.ac.uk/papers/spgW9.pdf
Which looks more promising than it likely is, they only run up to 12x12
Honestly it could even be 1, although that seems unlikely. 
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 04062015 15:31
(Original post by TheMagicMan)
Do you know of any definitive upper bound?
Honestly it could even be 1, although that seems unlikely.
This *may* be of use to you, I'm not sure I fully understand the problem you are discussing.
http://mathworld.wolfram.com/QueensProblem.html 
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 04062015 15:46
(Original post by Zacken)
I remember solving something called the 8Queens and investigating the nqueens problem as part of a programming course I took online some time back.
This *may* be of use to you, I'm not sure I fully understand the problem you are discussing.
http://mathworld.wolfram.com/QueensProblem.html 
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 04062015 18:01
(Original post by Zacken)
I remember solving something called the 8Queens and investigating the nqueens problem as part of a programming course I took online some time back.
This *may* be of use to you, I'm not sure I fully understand the problem you are discussing.
http://mathworld.wolfram.com/QueensProblem.html 
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 04062015 18:36
(Original post by TheMagicMan)
Yeah that problem is pretty easy and probably not relevant. At this point I'm pretty much convinced that there is no good way to analytically approach this problem as it is equivalent to a constrained optimisation problem that is likely not explicitly solvable. 
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 05062015 12:59
Hopefully, you'll find this nontrivial...
Problem 496 **
Find all such that
for all integers satisfyingLast edited by Renzhi10122; 05062015 at 17:23. 
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 05062015 14:19
(Original post by Renzhi10122)
Hopefully, you'll find this nontrivial...
Find all such that
for all integers satisfying 
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 05062015 14:21
(Original post by jjpneed1)
Is it just the zero function? It's [f(x)]^2 not f(x^2) yes? 
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 05062015 17:17
(Original post by Renzhi10122)
Hopefully, you'll find this nontrivial...
Find all such that
for all integers satisfying 
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 05062015 17:22
(Original post by ThatPerson)
What background knowledge is assumed here (as per the usual difficulty rating outlined in the first post)? I have a few ideas, but as I've never properly learned how to solve functional equations I'll leave it if it requires specialist knowledge.Last edited by Renzhi10122; 05062015 at 17:24. 
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 06062015 02:30
(Original post by Renzhi10122)
Hopefully, you'll find this nontrivial...
Given any , must there exist s.t. 
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 06062015 13:15
(Original post by Lord of the Flies)
You have odd tastes  this is very messy Not sure I can be bothered to finish. Here is something interesting:
Given any , must there exist s.t.
Ok, soSpoiler:Showif we let y=0, and f(0)=a, then we need which essentially says that if for some x, then we are done. So we can now say that for all x. So, we then let x=0 to get .
If then let s.t. and and so if for positive b, then we are done.
If then let s.t. and . The same logic follows.
If then and for .
Thus, we can further restrict the we will deal with to those that for , and for , .
And that's me done for now.

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 09062015 14:32
(Original post by Renzhi10122)
Hopefully, you'll find this nontrivial...
Problem 496 **
Find all such that
for all integers satisfying
Knew it looked familiar
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