| --- Log opened Wed Oct 07 00:00:42 2009 |
| 00:03 | <@Vornicus> | Rham: I wrote a post describing several different ways of doing division. |
| 00:06 | < Namegduf> | Switching between Python and C++ rapidly makes my head feel weird. |
| 00:12 | < Rhamphoryncus> | Vornicus: oh? Got a link? |
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| 00:56 | <@Vornicus> | http://community.livejournal.com/cs_lectures/4959.html |
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| 02:14 | < Rhamphoryncus> | Vornicus: ahh thanks. Is that in the context of C? |
| 02:16 | <@Vornicus> | This is in... no particular context. |
| 02:16 | <@Vornicus> | I don't know which ones are used where. |
| 02:16 | < Rhamphoryncus> | Well, it is language dependant. You implied it's hardware dependant |
| 02:17 | <@Vornicus> | It may be! I don't actually know. |
| 02:20 | < Rhamphoryncus> | doh, I was confusing python's negative dividend handling with that of negative divisors |
| 02:22 | < Rhamphoryncus> | It does follow your second example |
| 02:25 | | * Rhamphoryncus notes that ceiling division doesn't have a good matching modulo definition |
| 02:25 | <@Vornicus> | Indeed not. |
| 02:27 | < Rhamphoryncus> | hrm. It does have a modulo, but it's not a remainder |
| 02:38 | < Rhamphoryncus> | amusingly, wikipedia uses an example of a clock, but with 0 instead of 12 |
| 02:39 | < Rhamphoryncus> | modular arithmetic was introduced in 1801 o.O |
| 02:42 | <@McMartin> | We didn't really Get finite algebra until shockingly recently. |
| 02:43 | <@McMartin> | Group theory and such was still getting pretty ridiculously basic, important results well into the 20th century |
| 02:44 | | * Rhamphoryncus nods |
| 02:44 | < Rhamphoryncus> | yet we undoubtably used it, just not in a formal sense |
| 02:45 | <@McMartin> | A lot of it isn't useful until you get digital computers. |
| 02:46 | <@McMartin> | The group consisting of the set Z256 x Z256 x Z256 under addition, for instance, is basically a curiosity until it becomes the formal specification for 24-bit color mixing. |
| 02:46 | < Rhamphoryncus> | heh |
| 02:46 | <@McMartin> | (And is one of a vast number of groups with 2^24 elements, each with subtly different arithmetic behavior) |
| 02:47 | <@McMartin> | (But there are many more that look different but behave identically) |
| 02:47 | < Rhamphoryncus> | what's Z256 mean? |
| 02:47 | <@McMartin> | The integers, modulo 256. |
| 02:47 | | * Rhamphoryncus 's real knowledge is far too limited :( |
| 02:47 | < Rhamphoryncus> | oh THAT Z, heh |
| 02:47 | <@McMartin> | The Z should be all fancy and the 256 should be a subscript |
| 02:47 | <@McMartin> | The x there is "Cartesian Product" |
| 02:48 | <@McMartin> | There are two 4-element addition groups. |
| 02:48 | <@McMartin> | Z4, and Z2 x Z2. |
| 02:48 | <@McMartin> | Which is basically "two bits, added with carry" and "two bits, added independently" |
| 02:48 | <@McMartin> | One very fun result is that given the usual definitions of addition and multiplication for modular integer arithmetic... |
| 02:49 | <@McMartin> | Z_n is a properly formed field (that is, +, -, *, / all work, are all always defined except for division by zero, + is commutative, and the associative and distributive laws work) whenever n is prime. |
| 02:49 | <@McMartin> | Furthermore, every field with a finite number of elements in it ends up being exactly equivalent to Z_n (n prime). |
| 02:49 | <@McMartin> | Just with different names, basically. |
| 02:51 | < Rhamphoryncus> | aha, there it is! U+2124. Z??? |
| 02:52 | < Rhamphoryncus> | Interestingly, unicode now has a-z of that typeface. Most are outside the BMP though |
| 02:54 | < Rhamphoryncus> | heh. 52 entries, capital and lowercase, but 7 blanks because they were previously assigned elsewhere :) |
| 03:00 | < Rhamphoryncus> | ahh unicode. Now I can use x instead of x, even when I don't have an italic typeface available |
| 03:01 | | * Rhamphoryncus wonders if we might one day replace unicode with something integrating some style instructions |
| 03:04 | | * simon` is trying to install DrScheme |
| 03:06 | <@Vornicus> | <3 abstract algebra. |
| 03:08 | <@ToxicFrog> | <3 drscheme |
| 03:08 | <@ToxicFrog> | Prof today was extolling the virtues of APL |
| 03:09 | <@Vornicus> | .... |
| 03:10 | <@Vornicus> | Rhamphoryncus: "integrating some style instructions" usually says "HTML" nowadays. |
| 03:10 | <@ToxicFrog> | (APL is actually pretty sweet...if you have a keyboard that can emit heiroglyphics) |
| 03:11 | | Vornicus [vorn@ServerAdministrator.Nightstar.Net] has quit [[NS] Quit: ] |
| 03:12 | < simon`> | ToxicFrog, irssi |
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| 03:12 | | mode/#Code [+o Vornicus] by Reiver |
| 03:15 | <@ToxicFrog> | simon`: more wondering what os |
| 03:16 | < simon`> | ToxicFrog, I'm at my dept. terminal system running Gentoo through SunRay 270s. |
| 03:18 | < simon`> | my own laptop, which of its charger is broken these days, runs ubuntu. |
| 03:20 | < simon`> | meh |
| 03:20 | < simon`> | still segfaults. |
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| 04:26 | <@Derakon> | I will never understand why bc catches ctrl-C and prints a little message telling you to type "quit" to exit. |
| 04:26 | <@Derakon> | Why not just exit when you do ctrl-C? |
| 04:35 | <@Vornicus> | Okay, infix rules. Start in operand mode. If you see a unary operator or an lparen, push to operators and remain in operand mode. If you see an operand, push to the operand stack and switch to operator mode. Otherwise fail. |
| 04:36 | <@Vornicus> | When in operator mode, if you see an operator, pop-process all operators of /equal or lower/ priority from the operator stack before pushing. |
| 04:36 | <@Derakon> | What is this for? |
| 04:37 | <@Vornicus> | If you see an rparen, pop-process until you see an lparen (if you don't, fail). |
| 04:37 | <@Vornicus> | Writing a calculator. |
| 04:38 | <@Vornicus> | For postfix ops and parens, remain in operator mode. Otherwise switch to operand mode. |
| 04:38 | <@Vornicus> | At the end of the string, pop-process /everything/ - if you see an lparen, fail. |
| 04:41 | <@Vornicus> | hm, but exponentiation is associative in the other direction. |
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| 06:26 | | * Rhamphoryncus kicks xchat for somehow losing that nick highlight |
| 06:27 | < Rhamphoryncus> | Vornicus: HTML-ish, yeah. I don't know if I'd want to be limited to what HTML provides. I'd definitely not want to support even a significant amount of it |
| 06:29 | < Rhamphoryncus> | and hrm.. extensibility.. I don't want random shit payloaded in my text. |
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| 13:50 | <~Reiver> Quick math problem. This should be easy, but my brain is fail. |
| 13:51 | <~Reiver> You have a number sequence of x = x+4, so it goes 1,5,9,13,17,21,etc, up to 200. |
| 13:51 | <~Reiver> How many steps are needed to hit the cap? |
| 13:51 | <~Reiver> And what would the cumulative total be when they do? |
| 13:53 | < simon`> | 1) 25 |
| 14:04 | < simon`> | err, 50! |
| 14:05 | < simon`> | Prelude> sum (take 50 [x*4+1 | x <- [0..]]) |
| 14:05 | < simon`> | 4950 |
| 14:06 | < simon`> | err, so that'd be 51 steps to hit the cap. |
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| 16:59 | <@Vornicus-Latens> | a_k = a_{k-1} + n up to N is N // n if a_0 > N % n, and N // (n + 1) if a_0 <= N % n. |
| 17:01 | | Rhamphoryncus [rhamph@Nightstar-a62bd960.abhsia.telus.net] has joined #code |
| 17:02 | <@Vornicus-Latens> | That's if you include N in your list. if it's not included, use >= and < instead. |
| 17:02 | <@Vornicus-Latens> | And Reiver isn't here. |
| 17:02 | <@Vornicus-Latens> | Bastard. |
| 17:50 | | Derakon[work] [Derakon@Nightstar-d44d635e.ucsf.edu] has quit [[NS] Quit: Leaving] |
| 18:05 | | * SmithKurosaki confused |
| 18:07 | <@TheWatcher> | about 4 hours, 15 minutes ago Reiv asked a maths question. Vorn was just answering it, but Reiv quit 2 hours, 25mins ago |
| 18:08 | <@TheWatcher> | http://www.starforge.co.uk/irclogs/code/code.20091007.log.html#m1350-0 as a matteroffact |
| 18:09 | <@TheWatcher> | (also, I really need to fix up my log display code to handle ~ and & users ;.;) |
| 18:12 | < SmithKurosaki> | http://www.cracked.com/blog/using-windows-7-may-lead-to-murder/ |
| 18:24 | | Derakon[work] [Derakon@Nightstar-d44d635e.ucsf.edu] has joined #code |
| 19:35 | | * Derakon[work] finds a bug in the microscope code that looks roughly like this: |
| 19:35 | < Derakon[work]> | for i, item in enumerate(listOfItems): |
| 19:35 | < Derakon[work]> | for i, j in range(someNumber): |
| 19:35 | < Derakon[work]> | doSomething() |
| 19:35 | < Derakon[work]> | doSomethingElse() |
| 19:36 | < Derakon[work]> | The bug of course is that the value of the main loop's "i" gets changed in the inner loop. |
| 19:36 | < Derakon[work]> | What I find interesting, though, is that the right number of outer-loop iterations are still performed. |
| 19:36 | < Derakon[work]> | In other words, changing the value of i cannot cause you to skip (or repeat) loop iterations. |
| 19:45 | < gnolam> | Rargh. Virus warning chain letter. :P |
| 19:46 | | * gnolam sends it to Davy Jones's locker. |
| 19:48 | < gnolam> | Of course, telling Mailman to send it to the great grey void is the easy part. Sending a nastygram to the originator is the hard part. :P |
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| 20:03 | | crem [moo@Nightstar-8ca3eea7.adsl.mgts.by] has joined #code |
| 20:06 | < gnolam> | (Especially since I have to be /nice/ to her) |
| 20:11 | | Derakon[AFK] [Derakon@Nightstar-5abd3ac9.ca.comcast.net] has quit [Operation timed out] |
| 20:17 | < dmlandrum> | Just keep in mind, she really believes she's just trying to be helpful. :-) |
| 20:20 | < gnolam> | That's what I had to tell my self, over and over again. Through gritted teeth. :P |
| 20:25 | < gnolam> | In other news, Lagrangian mechanics and food poisoning don't really mix... |
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| 21:35 | < SmithKurosaki> | Oh? |
| 21:35 | < SmithKurosaki> | Also. You have succesfully found something you can't stab. Congrats! |
| 21:41 | | * gnolam stabs bacteria, Lagrangian mechanics and bicycle manufacturers with a rusty shiv. |
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| 21:54 | < SmithKurosaki> | Ouch. That's pretty harsh |
| 21:57 | < AnnoDomini> | Even beneficial bacteria? |
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| 23:44 | | You're now known as TheWatcher[T-2] |
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| 23:50 | < gnolam> | Hmm. I seem to have found a decent TFT screen at last. |
| 23:51 | < gnolam> | It's rather pricey, but it actually seems to do good colors together with good response times and input lag. |
| --- Log closed Thu Oct 08 00:00:57 2009 |