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Old 2007-08-03, 16:58   #12
xilman
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Originally Posted by R.D. Silverman View Post
Another example: We know that almost all real numbers are Transcendental.
The subset that is algebraic is countable, while the reals are uncountable.
Thus, the algebraic numbers have density 0 in the reals. But knowing that
almost all numbers are transcendental does not help us prove that e.g.
The Euler-Mascheroni constant is.
Even worse: almost all numbers are not computable by a Turing machine but, on the C-T hypothesis, we can't give even a single example!

Paul
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Old 2007-08-03, 17:00   #13
R.D. Silverman
 
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Even worse: almost all numbers are not computable by a Turing machine but, on the C-T hypothesis, we can't give even a single example!

Paul
Sure we can. One such example is:

For a given finite state machine, what is the probability that a random input
tape will halt?
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Old 2007-08-03, 17:38   #14
ewmayer
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Quote:
Originally Posted by R.D. Silverman View Post
For a given finite state machine, what is the probability that a random input
tape will halt?
Your Turing machine still uses a tape drive?!! You should consider upgrading.

[Fry's has specials on TMs nearly every week, you just need to be careful to read the fine print, send any rebate form in promptly, and make sure to save a copy of the latter in case it gets "lost" in the mail, as rebate forms appear to be distressingly prone to doing, similarly to insurance claim forms.]
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Old 2007-08-03, 20:37   #15
xilman
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Quote:
Originally Posted by R.D. Silverman View Post
Sure we can. One such example is:

For a given finite state machine, what is the probability that a random input
tape will halt?
Fair enough --- my statement was too sloppily phrased and should not have used "give". A more accurate verb would be "compute".

Even this statement needs tightening up a little. For instance, e is transcendental but we can compute it to an arbitrary but fixed precision and do so efficiently. Non-computable numbers are, by definition, non-computable.

Paul
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Old 2007-08-06, 12:06   #16
R.D. Silverman
 
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Your Turing machine still uses a tape drive?!! You should consider upgrading.

[Fry's has specials on TMs nearly every week, you just need to be careful to read the fine print, send any rebate form in promptly, and make sure to save a copy of the latter in case it gets "lost" in the mail, as rebate forms appear to be distressingly prone to doing, similarly to insurance claim forms.]
This is terrific! What is the price on a standard NDTM??? I'd like to buy one.
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Old 2007-08-06, 13:14   #17
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Even worse: almost all numbers are not computable by a Turing machine but, on the C-T hypothesis, we can't give even a single example!

Paul
Even weirder is the fact that if we work outside of the system, there can be an 'equal' number of non-computable numbers as there are computable ones. In other words, there is a countable model for the (standard) reals. And, of course, one could just work with the "computable" reals in the first place depending on which model one favors.
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