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#23 | ||||
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Nov 2003
746010 Posts |
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have gradients. Points in Q^2 do not. Quote:
algebraic variety and most definitely is discrete, Quote:
total cluelessness. diff of squares is NOT exponential because it is iterative. It is exponential because of the SIZE OF THE SEARCH SPACE Quote:
you are trying to do CAN'T work unless P=NP. Do you even know what exclusion moduli are? |
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#24 |
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Undefined
"The unspeakable one"
Jun 2006
My evil lair
11000010101002 Posts |
I found a proof that P=NP, and I would have posted it here but the margin is not big enough.
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#25 |
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Nov 2006
Singapore
10010112 Posts |
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#26 |
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Nov 2006
Singapore
3×52 Posts |
[QUOTE=R.D. Silverman;132912]
You just got added to my official list of cranks. This last remark shows total cluelessness. diff of squares is NOT exponential because it is iterative. It is exponential because of the SIZE OF THE SEARCH SPACE [QUOTE] Always thought the METHOD of searching is more important than the SIZE OF THE SEARCH SPACE. Of course what does a clueless crank know. |
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#27 |
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Nov 2006
Singapore
3·52 Posts |
Always thought the METHOD of searching is more important than the SIZE OF THE SEARCH SPACE. Of course what does a clueless crank know.
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#28 |
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Jul 2003
wear a mask
22·419 Posts |
Apparently, not much.
Plonk. |
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#29 | |
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Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
2·5,393 Posts |
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Not entirely sure I should have posted this observation for fear of casting confusion rather than enlightenment, but what the hell Paul Last fiddled with by xilman on 2008-05-07 at 12:21 Reason: Add non-trivial qualification. |
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#30 | |
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Nov 2003
22·5·373 Posts |
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as the difference of two squares. |
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#31 |
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Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
2·5,393 Posts |
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#32 |
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Nov 2006
Singapore
7510 Posts |
Read and reread this statement and I am still confused. I always thought that an algorithm is exponential ( or polynomial or linear) REGARDLESS of the size of the search space not because of it. And that your search space is defined by your problem and not your algorithm.
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#33 | |
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Nov 2003
22·5·373 Posts |
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Aho, Hopcroft, & Ullman is a good start. Garey & Johnson is excellent. Consider LP. A node traversing method such as Simplex is strictly exponential because the number of nodes is exponential in the size of the problem. Klee & Minty showed that any method for choosing a new basis variable at each step can require traversing ALL the nodes. However, modern LP codes rescale problems in a way that tends to destroy artificial problems such as Klee & Minty's so that Simplex works well in practice. (But it is still worst case exponential) OTOH, Khachian's algorithm is polynomial time, even though the search space (the volume of the feasible region) is exponential in the size of the problem. The size of the search space is determined by the problem. But a clever algorithm can reduce an exponential search space by a fixed fraction at each iteration and hence solve an exponentially sized problem in polynomial time. An interior point method also chops off a fixed fraction of the remaining search space at each iteration. Difference of squares methods are strictly exponential precisely because the abelian variety that is being search is really a scheme. (Think of it as a function space where the elements of the space are really just the rings you are trying to separate) There is no canonical ordering of points that makes one solution to N = pq where p,q, are RATIONAL any "better" than any other. Lacking such a metric, there is no way that any kind of algorithm that searches lattice points can determine the "best" direction to move when moving from one point to another. The worst case is that it must search exponentially many points to pass from a RATIONAL solution to Z. **IF** we had lattice basis reduction methods that could guarantee to reduce a basis vector by a fixed fraction at each iteration, we would have a poly-time factoring algorithm. But the "shortest-vector" problem is NP-Complete. LLL can reduce a basis vector somewhat, but it is not guaranteed to reduce it by a fixed fraction. |
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