Wikipedia:Reference desk/Archives/Computing/2018 December 20

= December 20 =

Samsung Session Expired Tone
I have a Samsung Galaxy J7, which, if I am correct, is running Android version 8.1.0. My question is that, sometimes, after I have been using it, and then have not been using it for a while, it pings me with an audible tone and says Samsung Session Expired. My question is: How do I get it to stop giving me an audible tone to say that my session expired? I don't really care what a Samsung session is, but I don't want to have to pick up the phone and look at it to see if I just got a text message when all that it is doing is telling me nothing. Can I turn these stupid tones off? Robert McClenon (talk) 03:25, 20 December 2018 (UTC)


 * The Internet has two solutions listed (I haven't tested these because I don't have a Samsung phone):


 * Keeping your Samsung account:


 * Tap Settings.
 * Scroll down and tap Samsung Account
 * press Cancel Sync
 * Reboot
 * Check your notifications and re-enter password if needed.


 * Nuking your Samsung account:


 * Open Settings
 * Select Accounts and Sync
 * Choose Samsung
 * Select your samsung account email
 * Tap remove account

--Guy Macon (talk) 16:42, 20 December 2018 (UTC)
 * Thank you. I will try the first.  Nuking the account isn't worth it.  Robert McClenon (talk) 18:40, 20 December 2018 (UTC)
 * Minor differences. Samsung Account is under Accounts.  Cancel Sync is done by turning off Auto Sync (and it then tells me that turning off auto sync saves some battery power but requires manual sync for data, but I am not trying to keep data synchronized between my desktop Dell, my laptop Dell, and my smartphone.  I don't want to live in a social media utopia, because a utopia is literally a no-place.  Robert McClenon (talk) 17:39, 21 December 2018 (UTC)

Samsung Not Giving Audible Tone
Is there a condition that sometimes prevents me from getting an audible tone when I receive a text message? (This is almost the opposite annoyance of the one mentioned above.) Or is this simply due to my having the phone in my pocket or being in a noisy place or having my car radio on loudly? Robert McClenon (talk) 03:25, 20 December 2018 (UTC)
 * As a test, you could send a message to yourself, with a 1 minute delay (scheduled message). Do it several times, with the phone in and out of your pocket. However, this doesn't help if you've assigned custom message tones for certain people. LongHairedFop (talk) 11:50, 21 December 2018 (UTC)

"Amoeba" "solves" NP-hard problem in "linear time"
This is really cool, but I think it's all a trick:. They have an "amoeba" (really, a true slime mold, Physarum polycephalum), which comes up with an approximate solution to the traveling salesman problem in apparently linear time. The amoeba has help from a computing process that looks at whether its "solutions" to the problem have inconsistencies: it has a channel for which numerical order each city is visited in, so say B1 to B5 for whether city B is visited first or fifth, and if any number or letter is visited by one pseudopod all the conflicting channels get hit with light to make others retract.

My assumption is that because they claim to have a decent simulation for the amoeba, which works in "almost linear time", using only N^2 parallel processors I assume, then they can't possibly get to beating exponential time unless they have solved the NP-hard problem in computer science by having an "amoeba" show them how to code. So I would suppose that they are modelling an exponential using a polynomial for some limited N and then eventually something will go drastically wrong, even though they say they want to get a bigger photolithography apparatus to make thousands of channels for the plasmodium to travel into.

Question is, am I right about this? It's not really within my competence, and if they have a magic tool to break our encryptions I ought to find out. Wnt (talk) 15:35, 20 December 2018 (UTC)


 * As you have described it, it isn't necessarily a trick or a breakthrough. I haven't read the paper, but you say that it comes up with an approximate solution in linear time.  That isn't theoretically interesting.  The crux of the problem has never had to do with approximate solutions.  What is NP-complete is finding an exact solution.  The amoeba is probably just a device for implementing a greedy algorithm, and greedy algorithms usually work very well on the traveling salesman problem.  They just don't always work, and occasionally they get stuck.  A greedy algorithm is used in road navigation systems, and usually works very well, but doesn't always come up with the best answer, and once in a while the navigation system can send you in a circle around the destination.  There isn't anything special about approximate solutions.  The problem is that finding an exact solution is NP-hard.  Robert McClenon (talk) 16:44, 20 December 2018 (UTC)


 * They say the time grows linearly as the number of cities increases from four to eight. I can do that with ease: just build in some sort of inefficiency that makes the four-city case take longer.


 * But can it be done without such trivial cheating? See Why My Soap Film is Better than Your Hadoop Cluster


 * Nature solves such physical systems automatically, for instance the n-body problem. There is a physical way to sort in linear time: cut a stick to the length of each of the items to be sorted.  Bang one end of them on the desk, then start picking the tallest one, repeat.  Bubba73 You talkin' to me? 04:11, 21 December 2018 (UTC)


 * BTW, as far as I know, no widely-used cryptography system is based upon traveling salesman. Now if they found a faster way to solve elliptic curve or pairs of large primes, that could break some popular algorithms. --Guy Macon (talk) 17:08, 20 December 2018 (UTC)
 * Having read the Wikipedia article, I see that this observation is very interesting biologically. It seems that the amoeba or slime mold has some sort of memory at a cellular level that is not in the nervous system that it does not have.  This may provide insight into the evolution of the nervous system, for instance.  However, it isn't interesting mathematically.  The significance to crypto is that crypto would be one of the many interesting results of solving NP-complete problems.  But this isn't a solution to an NP-complete problem, since the traveling salesman problem isn't to find an approximate solution, but an exact solution.  An exact solution to traveling salesman would be a solution to every NP-complete problem.  Would be.  Robert McClenon (talk) 18:39, 20 December 2018 (UTC)
 * The nervous system angle was what attracted me to the article to begin with, but in this particular case, it sounds like there is nothing very sophisticated going on. The pseudopods are retracted in response to light, contributing cytoplasm to a central storage, and the cytoplasm evenly expands everywhere until light shines on it again.  There was some commentary about synchronized waves of expansion (I think it was) but their simulation didn't need to implement them, and AFAICT they just meant more pressure throughout the whole organism at once. Wnt (talk) 15:50, 21 December 2018 (UTC)