Wikipedia:Reference desk/Archives/Computing/2020 April 4

= April 4 =

I got some wonder about computing Fibonaci rank N term, polynomial time
the idea of computing S=1+2+3+...+N in polynomial time by reducing the higher of its half to the lower of that one, I guess that can be adapted to compute the N rank term of the Fibonaci term, by computing first the "N/2" rank term, resulting some polynomial time wasting, for some floating point etimation of course. Is this looking to You more like an well known idea or rather some original stuff. I looked into wiki about Fibonaci series but its too big article for me to read. thank you!Florin747 (talk) 16:45, 4 April 2020 (UTC)


 * Fibonacci number gives closed form expressions for computing Fibonacci numbers directly. Your question is more of a math question than a computer question, btw.  — Preceding unsigned comment added by 2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 21:42, 4 April 2020 (UTC)


 * The last paragraphs of the section Matrix form of that article give an efficient way to compute Fibonacci numbers with a high index. Avoiding recomputation is absolutely essential, but it is simpler to use tupling instead of memoization, expressing the recursion in terms of tuples $$T_n = (F_{n-1}, F_n)$$. --Lambiam 09:20, 5 April 2020 (UTC)

Hi, I think that Your reply/replies are more than enough for me. Thank You, Florin747 (talk) 13:34, 5 April 2020 (UTC)

Why does my updated entry not appear once I'm logged out
I have spent the afternoon updating my wiki entry. Once I am logged out, I cannot see it and it reverts back to the old entry. When I am logged in, I can see the updated entry. Does anyone know why this is? — Preceding unsigned comment added by JCQCBR (talk • contribs) 18:33, 4 April 2020 (UTC)
 * Your edits were actually reverted as unsourced. Please, read Reliable sources before repeating them. Ruslik_ Zero 20:58, 4 April 2020 (UTC)


 * It looks like your edits to John Cooper (barrister) were reverted because you did not link to any sources.
 * New material needs to be sourced, you can't write it from your own personal knowledge.
 * Here is Wikipedia's policy on sourcing : Reliable_sources
 * Also if you are John Cooper (barrister) you probably shouldn't be editing the article at all, as it probably contravenes Wikipedia's policy on conflicts of interest. COISELF
 * Adding a request that someone else edit the article to the article's Discussion ("talk") page is perfectly acceptable, and recommended in such cases.
 * Hope this helps. ApLundell (talk) 20:59, 4 April 2020 (UTC)

Phone battery crapping out suddenly
I have an old Nokia phone that I don't use very much, but the battery charge up til recently has tended to last for a few days on standby, which is good enough for me. Yesterday I tried to make some phone calls and they didn't go through, and also the battery pooped out rather quickly, going from 100% to around 25% in less than a day. I asked someone online who told me that the networks are slammed because of covid-19 which is affecting call completion, and also increasing battery drain if the phone has to reach faraway towers (fwiw the phone shows around 4 out of 5 signal bars). Last night the phone was charged to around 75% so I put it in "flight mode" which should disable the radios, but it discharged completely during the night anyway.

Does anyone know if it's a common failure mode of batteries to go from having reasonable to very low runtime suddenly? I'm used to them getting weaker more gradually. The phone and battery are 5+ years old though, so it doesn't surprise me if the battery is due for replacement. Unfortunately getting a replacement battery during the Covid lockdown might not be so easy. I guess I can leave the phone plugged into a charger since I'm stuck at home anyway, but I don't have a landline so this is how I make phone calls. Phone is on AT&T GSM network if that matters. Any idea how to find outage status in East bay, California? Thanks. 2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 21:49, 4 April 2020 (UTC)
 * Yes, this is often what happens when a battery is old. That's pretty old for a lithium-ion battery, which is probably the battery type. You can probably buy a replacement battery online though right now shipping may take some time. But you might as well just get a newer phone; you can get very good smartphones these days for cheap (consider buying used). If you're low-income look into Lifeline and charity options.
 * Personal opinion: this is one of several reasons to keep at least local landline service, which is generally pretty cheap. You want emergency number access, and landlines are much more reliable than cellular for this. But make sure you have at least one wall-powered phone, meaning one that doesn't need mains power, in case power goes out. --47.146.63.87 (talk) 23:33, 4 April 2020 (UTC)
 * Note that again, this depends a lot on where you live and what 'landline' means. I don't know what things are like in East bay, I imagine it depends a lot on the specific location with East bay. But here in Auckland, I have gigabit fibre. A 'landline' can either be provided by the ONT, which very few providers do, or by the router SIP gateway. Some providers don't even let you get a landline through them, requiring you to deal with some other company for it. For a landline through the ONT, given the way it works there is perhaps a slightly higher chance it will survive even if your internet access dies. For the latter, no. Since it's with the same provider you do perhaps have a slightly higher chance that it will work even if your internet is having problems than going with a separate provider for your landline. But either way no UPS or battery backup is provided. You need to provide your own for the ONT and perhaps router. Given that, you can likely provide power for your cordless phone anyway. (Many cordless phones can work without power, you put the handset on the base and use them although this is likely to be somewhat annoying in an emergency.) Once you get fibre installed to your house, they generally try to disconnect the copper network. While you may be able to convince them not to, and maybe you can even let them convince you to keep a copper line, it's definitely not what I'd call cheap to do so. As for "much more reliable", again I think it's complicated. During the February 2011 Christchurch earthquake, from what I've read before, the copper landline network did often survive reasonable well but of course there were quite a lot of faults too. The mobile network also did fairly well, in terms of surviving but of course tends to have capacity issues quite a lot more. I think landlines (copper) phones did have a greater chance of working but definitely there were cases when you could make mobile calls but your landline was broken. The biggest advantage IMO is probably having 2 options, rather than assuming one is more likely to work. Nil Einne (talk) 07:54, 5 April 2020 (UTC)
 * Right, the more options the better, but most people have mobile phones these days and are going without landlines. Another factor with emergency services: landlines have a fixed location that is often automatically available to dispatchers, while this can be an issue for mobile phones. It's improved somewhat with things like Enhanced 911 in the U.S., but still not always as good. --47.146.63.87 (talk) 21:27, 5 April 2020 (UTC)
 * Very weird thing, the phone powered itself off when the battery ran completely out. I recharged it (this was about a day ago) and it seems to be holding charge ok now.  I wonder if it got into some mode where it was using more power than usual until the power cycle. I do have another phone I can swap the sim card into if I have to, but I like my old Nokia.  I can probably also figure out how to make wifi voip calls if it comes to that, but I don't use phones much these days so it is ok.  Thanks for the responses.  2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 20:36, 5 April 2020 (UTC)
 * Note that allowing li-ion batteries to discharge fully is bad for their health, though I'm not sure it'll matter much anymore. Don't be surprised if it continues to be flaky; li-ions inevitably degrade over time, regardless of how or if they're used. I'll elaborate on something since you seemed to be confused about the battery charge levels. These are always just an estimate by the phone. Newer, more expensive phones can sometimes be more accurate since they often have access to lots of complex data from the chips inside the battery; less sophisticated devices may only know the output voltage of each cell. Assuming your phone was in fact in airplane mode, it presumably didn't "use up" the whole 75% charge; the battery output voltage dropped because the battery can't sustain it due to wear, and this causes the phone to show less charge. You said you're used to batteries getting weaker more gradually, but different battery types behave differently. If you're thinking of rechargeables in cheaper things like electric toothbrushes, or AA/AAA rechargeables, those are NiCd and NiMH batteries. --47.146.63.87 (talk) 21:27, 5 April 2020 (UTC)
 * Thanks. I'm used to lithium batteries (in laptops, say) gradually degrading, and I've heard the ones in electric cars act similarly.  I'll see how this phone battery holds up going forward, but I'll also replace the battery (will have to order a new one from someplace) once it's easier to get stuff like that.  Anyway this battery situation is just a minor annoyance, and we all have much more significant things to worry about.  2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 02:37, 6 April 2020 (UTC)