Wikipedia:Reference desk/Archives/Computing/2016 February 7

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February 7

Is there any computational method that's neither a numerical method, nor a symbolic method?

Is there any computational method that's neither a numerical method, nor a symbolic method, nor a combination of both? I cannot imagine another possibility, but my lack of imagination is definitely not a proof.--Llaanngg (talk) 00:42, 7 February 2016 (UTC)

What do I get when I divide one by three?

• Numerically, I get 0.33333333....
• Symbolically, I get 1/3 (read: "one divided by three").
• Verbally Conceptually, I simply get: a third.

HOTmag (talk) 01:03, 7 February 2016 (UTC)

Verbally = symbolically. --Llaanngg (talk) 01:52, 7 February 2016 (UTC)

@Llaanngg:: 1/3 is "one divided by three" (just as 1/x is "one divided by ex"): it's symbolic, i.e. it contains some symbols, e.g. "divided by" and likewise. It's not the same as "a third", being the conceptual computation.

Please note that not every computation can be made conceptually, just as not every computation can be made symbolically: For example:

• The solution of the equation 3x=1 can be reached, both symbolically - as 1/3 (read "one divided by three"), and conceptually - as "a third".
• The solution of the equation x²=2, can be reached symbolically - as √2 (read: "square root of two"), but cannot be reached conceptually.
• The solution of the equation x⁵+x=1, cannot be reached conceptually nor symbolically.

Btw, there is also the "geometric computation". For example: the solution of the equation x²=2, can be computed - not only symbolically as √2 i.e. as "the square root of two" (and also numerically of course) - but also geometrically as the length of a diagonal across a square with sides of one unit of length.

HOTmag (talk) 07:41, 7 February 2016 (UTC)

Fuzzy logic ? StuRat (talk) 01:54, 7 February 2016 (UTC)

On one hand "numerical" is a kind of symbolic reasoning. On the third hand, if you can think nonsymbolically, then you can compute nonsymbolically. With yet another hand, graphical calculations are possible, such as Euclidean constructions using compass and straight edge. GangofOne (talk) 02:21, 7 February 2016 (UTC)

Computable real arithmetic is arguably not numerical (since I think "numerical methods" are approximate by definition) and arguably not symbolic (since it works with computable real numbers "directly", not formulas). -- BenRG (talk) 02:44, 7 February 2016 (UTC)

Neural networks could be counted as neither. Fuzzy logic might also fit there too, but you could argue that all of these are symbolic, as the computation has to represent something in the problem. Graeme Bartlett (talk) 10:19, 7 February 2016 (UTC)

Neural network uses numerical methods: the errors in the output converges to a minimum, so the output approaches a numerical value. Fuzzy logic uses symbolic methods, as you've indicated. HOTmag (talk) 10:32, 7 February 2016 (UTC)

The terms are kinda vague - but I'd definitely want to add "geometrical" to "symbolical" and "numerical". There are some wonderful things that can most easily be visualized geometrically...the dissection proofs of pythagoras' theorem come to mind here, but there are many good examples out there. SteveBaker (talk) 16:12, 7 February 2016 (UTC)

Analog computers were once used to solve differential equations. Also even now people use scale models for architecture, hydrology or wind tunnel simulations. Graeme Bartlett (talk) 00:59, 8 February 2016 (UTC)

Standard digital computers can be understood as doing everything by symbolic methods, including numerical computation; and the way I see the word "computation", that's really the only kind there is. However, you may consider what an analog computer does to qualify as computation (rather than as an alternative method used instead of computation). In that case it would qualify as an answer. --76.69.45.64 (talk) 23:13, 7 February 2016 (UTC) (by edit request) ―Mandruss ☎ 06:45, 8 February 2016 (UTC)

Scraping of .asp?

How can I scrap a page accessed with www.address.org/somescript.asp? It has two fields (name of artist, works) and two buttons (search, reset). How could I tell a program to go to name of artist, pick a name from a list that I have stored, press search, retrieve page and store. --Scicurious (talk) 16:36, 7 February 2016 (UTC)

wget has parameters to fill in forms. Also if all the names are linked or are findable on a query, you may be able to do a recursive query to get all the pages. Otherwise you could make a list of URLs and pass that to wget. Graeme Bartlett (talk) 00:54, 8 February 2016 (UTC)

Go through the whole process once or twice manually. Is there something similar each time, e.g. the button to be clicked is always in the same place, or the text you need is always formatted the same way? If so, you could perhaps use Macro Express to automate the process; it has the ability to control mouse placement (so you could automatically move the cursor to a certain space, for example) as well as merely clicking and pressing keys. Since you have the list of names, you could have it copy/paste from the list. Code for that operation follows my signature. Nyttend (talk) 01:12, 8 February 2016 (UTC)

Extended content

[Save your list in Notepad if you're using Windows, or a comparable no-frills file if you're in a Mac. Place your cursor at the top of the list before starting your macro. Be sure to have each name in a separate line of the file.] <SHIFTD> <END> <SHIFTU> <CTRLD> C <CTRLU> [insert the menu command to activate your web browser window] [insert commands for searching and retrieving the page] [the following assumes that it's CTRL+S to save] <CTRLD> S <CTRLU> [insert the menu command to activate your Notepad window] <HOME> ` <END> [insert the menu command for a right arrow key press]

With a macro program like MacroExpress, it's just simulating the keystrokes that you'd be using anyway, so just write down the keys you'd press and have the program press those keys in those orders. Be careful about timing: the computer often takes slight bits of time to load windows, and while this isn't significant when you're doing things manually, it's significant for the macro, which essentially does everything instantaneously. As a result, you'll need to insert slight timing breaks (very rarely will you need anything more than a couple hundred milliseconds) after commands that bring up new windows to ensure that it has time to bring up the window before you have it start performing things in the window. Also, you should use something like Notepad, because it won't insert additional characters, and every character matters in this kind of setting. Things like C are instructions to type whatever you've written, while things within <> characters are instructions to press specific keys instead of writing those letters: CTRLD is push down the control key, CTRLU is let it up, and the same for SHIFTD/U. Since you have a list of names in Notepad, with each name on a separate line, you'll find it helpful to mark which ones you've done. I've told it to place a ` character at the start of each line with an already saved title (after it saves the page, it adds the character before the name, and then goes to the next line, where it's ready to start the next page) because that's an easy way of marking which lines you've already done, and the ` character, being quite rare in normal text, isn't likely to be found elsewhere in the document, so when you're done with the list, you can simply do a find/replace command in Notepad to delete the character, and you won't worry about deleting significant characters. Nyttend (talk) 03:59, 8 February 2016 (UTC)

Time Machine's persistence

My external HD has suddenly become unreliable. (Nothing vital is on it.) It could be some time before I can replace it. I currently have about six months of Time Machine backups. If a year goes by before I replace the flaky drive, will Time Machine throw away what was on it, or keep the last known versions of those volumes? —Tamfang (talk) 21:58, 7 February 2016 (UTC)

The question is unclear. Time machine will keep adding back ups as long as there is space on the drive, once the drive is full it will delete the oldest backups to make space. How much room it needs depends on how many changes you have made since the last time it backed up. Does that answer your question? Vespine (talk) 05:27, 9 February 2016 (UTC)

My reading of this question is that the flaky drive and the Time Machine backup drive are different devices, and OP would like to know: if they scrap the flaky drive and leave it unreplaced for a while, will Time Machine preserve the last known backup of that drive indefinitely, on whatever external drive it is using as a destination, even while it replaces backups of other drives that are still available. Perhaps OP could confirm? 94.12.79.130 (talk) 22:21, 15 February 2016 (UTC)