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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: olcott Newsgroups: comp.theory Subject: Re: Simulating termination analyzers by dummies --- What does halting mean? Date: Wed, 19 Jun 2024 09:05:29 -0500 Organization: A noiseless patient Spider Lines: 120 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Wed, 19 Jun 2024 16:05:29 +0200 (CEST) Injection-Info: dont-email.me; posting-host="c0498080d6b8a2710b4ab7de903a0762"; logging-data="2090688"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19qWYuzTwKnk494DZEh/bsv" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:uDIA1xIMWiD9GyoKOibou+3ye8M= Content-Language: en-US In-Reply-To: Bytes: 5833 On 6/19/2024 4:29 AM, Alan Mackenzie wrote: > olcott wrote: >> On 6/18/2024 4:36 PM, Alan Mackenzie wrote: >>> [ Followup-To: set ] > >>> In comp.theory olcott wrote: >>>> On 6/18/2024 12:57 PM, joes wrote: >>>>> Am Tue, 18 Jun 2024 12:25:44 -0500 schrieb olcott: >>>>>> On 6/18/2024 12:06 PM, joes wrote: >>>>>> void DDD() >>>>>> { >>>>>> H0(DDD); >>>>>> } >>>>>> DDD correctly simulated by any H0 cannot possibly halt. >>>>>>> DDD halts iff H0 halts. > >>>>> So H0 returns "doesn't halt" to DDD, which then stops running, >>>>> so H0 should have returned "halts". > >>>> This was three messages ago. >>>> I had to make sure that you understood that halting >>>> does not mean stopping for any reason and only includes >>>> the equivalent of terminating normally. > >>> No. You're wrong, here. A turing machine is either running or it's >>> halted. There's no third alternative. If your C programs are not in one >>> of these two states, they're not equivalent to turing machines. > >> Although I agree with this there seems to be nuances of >> disagreement across the experts. > > I doubt that very much. The whole point of turing machines is to remove > ambiguity and unneeded features from the theory of computation. A third > alternative state is unneeded. > Some people say that a TM can halt in a non-final state. >>>> DDD correctly emulated by H0 DOES NOT TERMINATE NORMALLY. > >>> There is no concept of "normal" termination in a turing machine. The >>> thing is either running or it's halted. > > >> I develop one within the conventional notions below. > > You don't need it. You just confuse yourself (and possibly others) with > it. What you call the "aborted state" is just one more final state for > the TM to halt in. > When the adapted UTM halts after simulating ten state transitions of a Turing Machine Description that only loops we cannot correctly say that the looping input has halted. When the adapted UTM halts after recognizing the repeating state of a Turing Machine Description that only loops and transitions to its reject state then this adapted UTM is a halt decider for inputs that only loop. >>>>>> Some TM's loop and thus never stop running, this is classical >>>>>> non-halting behavior. UTM's simulate Turing machine descriptions. >>>>>> This is the same thing as an interpreter interpreting the source-code of >>>>>> a program. >>>>> Some TMs do not loop and do not halt. > >>>>>> A UTM can be adapted so that it only simulates a fixed number of >>>>>> iterations of an input that loops. > >>> As has often been said, it is then no longer a universal turing machine. > So what? > >> None-the-less it does derive the notion of abnormal termination >> as applied to Turing Machines. > > As I said, that is not a useful notion. It just confuses. > It is a perfectly useful notion as I have defined above because the adapted UTM becomes a halt decider for inputs that only loop. >>>>>> When this UTM stops simulating this Turing machine description we >>>>>> cannot correctly say that this looping input halted. > >>> Yes, we can. It has been designed to count to 42 then halt. It is then >>> in the halted state. > > >> Two different machines. >> (a) The TM description of a looping machine. >> (b) A UTM that has been adapted to count to five repeating >> states before it aborts its simulation of the looping machine. > > (b) is not a universal turing machine. It is a TM, one of whose halting > states is having counted five repeating states. > >>>>> Yes. We also cannot say that that input was simulated correctly. > >>> Indeed, not. > > >> It is a mistake for a simulating termination analyzer >> to simulate infinite repeating states. > > How can that be a "mistake" if it's what the thing is programmed to do? > Termination analyzers are required to halt so it fails to meet its spec. >> -- >> Copyright 2024 Olcott "Talent hits a target no one else can hit; Genius >> hits a target no one else can see." Arthur Schopenhauer > -- Copyright 2024 Olcott "Talent hits a target no one else can hit; Genius hits a target no one else can see." Arthur Schopenhauer