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420chan is Getting Overhauled - Changelog/Bug Report/Request Thread (Updated July 26)

Linear Programming (Decision Mathematics Query)

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- Fri, 28 Oct 2016 13:53:23 EST tyLg+ghU No.15252
File: 1477677203056.png -(7991B / 7.80KB, 293x289) Thumbnail displayed, click image for full size. Linear Programming (Decision Mathematics Query)
I am having difficulty formulating the following in terms of linear programming

A pig farmer uses at least 800kg of feed daily. The feed is a mix of corn and maize.
The special feed mixture must contain at least 25% protein and a maximum of 6% fibre

The composition of corn per kg is as follows:
Protein: 32g per kg ; Fibre; 27g per kg ; Price £ 0.3 per kg

The composition of maize per kg is as follows:
Protein: 360g per kg ; Fibre: 65g per kg ; Price £0.9 per kg

What is the minimum daily cost for the farmer, for food with at least 25% protein and max 6% fibre.

I initially poised the following

Let var1 = Corn_inKG // the amount of corn in kg
Let var2 = Maize_inKG // the amount of maize in kg

Minimise the following cost:
y = (£0.3)*(Corn_inKG) + (£0.9)*(Maize_inKG)

Total Protein:
0.032kg*(Corn_inKG) + 0.360kg*(Maize_inKG)

Total Fibre
0.027kg*(Corn_in_KG) + 0.065kg*(Maize_inKG)
Comment too long. Click here to view the full text.
Beatrice Sushspear - Fri, 28 Oct 2016 16:54:06 EST ZjFavw7f No.15253 Reply
Without more information I would assume that you can take the amount of feed the farner needs to be exactly 800kg. Since there is no deal or discount for buying more corn or maize, any additional mass of feed will cost more money. As you are asked to minimize the cost to the farmer, you should always use the least mass possible.

Now it may be that you cannot minimize the cost and attain 800kg at the same time without buying some fraction of a kilogram of feed. This is probably why the question says "at least" 800kg. You will then need to take your answer and round up to the nearest integer if the feed is sold strictly by the kg and not just weighed en masse.
George Foffingworth - Mon, 31 Oct 2016 09:30:26 EST tyLg+ghU No.15260 Reply
Thank you, this was the only information provided so I shall do as formulated in OP. Thank you Beatrice Sushspear

muh math

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- Mon, 16 May 2016 20:04:48 EST RHLOntyV No.15119
File: 1463443488476.png -(203128B / 198.37KB, 423x314) Thumbnail displayed, click image for full size. muh math
Is mathematics a discovered (natural) or man-made phenomena?
Personally I think it's natural because it can precisely describe natural events and laws which those events must conform to.
Thoughts on this?
15 posts and 1 images omitted. Click View Thread to read.
Mr. Schwitters - Sun, 16 Oct 2016 00:37:47 EST xB0tAwHQ No.15244 Reply
1476592667678.jpg -(172000B / 167.97KB, 472x570) Thumbnail displayed, click image for full size.
It's both natural and man-made. Look at that documentary where Zizek is standing in a pile of garbage, and saying, "This is the most natural thing in the world!". Nature is man. Culture is nature. Man is not separate from nature. You can't take biology out of the environment from which the gene evolves.

Well, you hear "Time/space/maths doesn't exist, man" so often. But for whom does it not exist?

I perceive its existence. How do I perceive it? Through my nervous system. My nervous system is receiving billions of signals every second.

Luckily there is a brain there which categorizes those signals for me into distinct tracks based on what has been evolutionary fit. That way, when I see a bear in the forest, I don't take out my ruler and try to measure every hair on his body in order to determine if the bear is a threat. Automatically my brain detects a threat and different glands fire off hormones, etc. and I find some way to keep my pic-a-nick basket.

To get a real answer to this, you have to look at the nervous systems evolved through time, and how nervous systems react to the phenomenal world. We still have amoeba, reptile, mammal, etc. sense, and that affects our perception. The 'tracks' where we store imprints about previous threats/comforts determines our perception.

Euclidean geometry is only an explanation of the world as it relates to the perception of domesticated primates.

We wouldn't see space in 3D if our nervous systems were different. We wouldn't plot points in 3D space if our nervous systems were different. Phenomenal existence only appears as it does because we evolved through all of the other species in the environment and atmosphere that we did.

tl;dr perception is everything, practice magick and cast spells dude
Shitting Trotdale - Sat, 22 Oct 2016 10:53:25 EST ussIY8P4 No.15250 Reply
>We wouldn't plot points in 3D space if our nervous systems were different.

No, we would still plot points in space regardless of how we evolved. Euclidean geometry may be somehow ``favored'' by our biology because it is a good local approximation of the acutal curved space in which we live, but even if a creature evolved in a truly alien geomtery it would still make up the geometry we live in if it was intelligent, just like how we have made up infinite families of alien geometries that don't obviously correspond to our physical reality.


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- Sun, 25 Sep 2016 22:57:20 EST Z131bdYa No.15216
File: 1474858640046.jpg -(29044B / 28.36KB, 747x210) Thumbnail displayed, click image for full size. uhhh
Can someone please explain to me what's happening here?
The idea of a fraction being made up of other fractions is already weird to me, but why is the answer just flipping them?
4 posts and 1 images omitted. Click View Thread to read.
George Dezzlesudging - Fri, 07 Oct 2016 21:30:10 EST GmQCz3Ds No.15238 Reply
1/2 over 1/4. you flip 1 wrong fraction and multiply the 2 fractions together.

instead of .5 / .25 you're doing .5 times 4.
Lillian Daddlekeg - Sat, 08 Oct 2016 22:03:58 EST A2j/BW/W No.15241 Reply
(1/x)/(1/y) = 1*(1/x)/(1/y) = (xy/xy)*(1/x)/(1/y) = (xy/x)/(xy/y) = y/x

If you multiply the numerator and denominator of a fraction by the same value, the value of the fraction stays the same. Here you're just multiplying the top and bottom of the fraction by 2^5*7^2. The 2^5s cancel in the top and the 7^2 cancel in the bottom.

Help evaluate this integral?

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- Sun, 25 Sep 2016 02:55:07 EST os0KtXjb No.15214
File: 1474786507368.jpg -(6748B / 6.59KB, 180x130) Thumbnail displayed, click image for full size. Help evaluate this integral?
So I'm working on a Calc II assignment, and I'm stuck on a problem that asks for the volume of the infinitely long solid attached.

f(x) = xe^(-x^3), so I can prove that the integral converges. I'm a lazy cunt so I used Wolfram Alpha to evaluate the integral and the answer involves the gamma function, which puts solving it beyond the level of this class.

So is there a more obvious way to go about this problem, or did my prof. assign a problem that we can't actually do at this level?
3 posts omitted. Click View Thread to read.
Hannah Wummerham - Wed, 05 Oct 2016 14:21:15 EST QUTqUdS2 No.15236 Reply
Yes you integrate by parts, no need for a Gamma function.
Charlotte Cunkinfoot - Fri, 07 Oct 2016 20:57:03 EST q1podWFh No.15237 Reply
I tried this. It only takes a u-substitution this way.

Also, the gamma function can be covered in a class at this level, although it isn't needed here.
Lillian Daddlekeg - Sat, 08 Oct 2016 21:13:04 EST A2j/BW/W No.15240 Reply
This. The integrand is pi*x^2*e^(-2x^3). Set u = -2x^3, the answer comes out to be pi/6.


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- Wed, 28 Sep 2016 20:51:12 EST dJCwm4mq No.15225
File: 1475110272932.jpg -(450342B / 439.79KB, 1920x1080) Thumbnail displayed, click image for full size. 10101011010101
When u come onto the math board
Beatrice Subberbanks - Fri, 30 Sep 2016 16:50:22 EST 9fX9//hV No.15231 Reply
What in the blue fuck are you talking about?
Charlotte Brezzlecheg - Fri, 30 Sep 2016 17:11:16 EST ZD4TCLS2 No.15232 Reply
I think that by posting a picture of the green vertical "code" from the movie The Matrix along with a binary string for a subject the OP is trying to indicate that they felt awed by the discussions taking place here.

Basic trig question

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- Tue, 13 Sep 2016 14:35:19 EST wFiRC6TB No.15197
File: 1473791719735.jpg -(9753B / 9.52KB, 250x154) Thumbnail displayed, click image for full size. Basic trig question
Ok so long story short - my math teacher this semester is the wort teacher ive ever had in my entire life. Asked him what formula they used to cme up with the xy coordinates on a unit circle. Example: terminal leg of 45* aka pi/4 on the unit circle intercepts at p=(root2/2, root2/2). He said there is no formula you just have to memorize. Are you kidding me i studied the chapter over and over and realized its the pythagorean theorum no matter what the radius equals. What a shit teacher.

Anyway my question is how does sin=y, but the fundamental idenitity of sin is 1/csc? Does this mean that y=1/csc?
Part 2: can that one be interchanged with any value of r? For example does it apply for circles that are not unit circles?

I know this is super basic, and my book explains it in a complex way, but its not like i have a good enough teacher to ask any questions to fill in the holes. Ive had straight a's and b's in my previous classes up til this guy.
5 posts and 3 images omitted. Click View Thread to read.
Vesuvius - Sat, 17 Sep 2016 11:24:58 EST 9fX9//hV No.15203 Reply
it's like asking why do we call dogs, dogs? Because that's just what we call them.
John Bundlefoot - Sun, 18 Sep 2016 04:18:43 EST 9fX9//hV No.15205 Reply
I should say the same to you.
John Bundlefoot - Sun, 18 Sep 2016 04:20:21 EST 9fX9//hV No.15206 Reply
I never said I didn't understand the post. I said you were overcomplicating it. If you don't understand the difference you probably shouldn't be giving people advice about anything.

Sett theory

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- Thu, 01 Sep 2016 05:16:48 EST NsqdJ6Lc No.15184
File: 1472721408300.jpg -(2195808B / 2.09MB, 3920x2204) Thumbnail displayed, click image for full size. Sett theory
Is there a way to find the equivalence relation corresponding to any partition?
Like p = {{1,4,7},{2,5,8},{3,6},{9}} with is an example i have in front of my nose. Can I find the relation from wich i get that partition of {1,2,3,4,5,6,7,8,9} ?
For the record I think not, but I only read about this stuff last night.
5 posts and 1 images omitted. Click View Thread to read.
Charlotte Gobberhood - Tue, 06 Sep 2016 18:06:06 EST 4JPlB6jB No.15190 Reply
>This is the same as having that b in P_i and a in P_i, so (b,a) in R, so the relation R is reflexive.
This should say symmetric at the end instead of reflexive.

>manually define an equivalence
Do you mean the realtion induced by a partition or something else? I'm not sure what constitutes "manually" defining a relation. Also, it's not rigorous to say that
>numbers are in the equivalence class here if they are 3 more than some other number in the equilance class
since the partition {{1,4,7},{2,5,8},{3,6,8}} also has that property and induces a different equivalence relation.
Charlotte Gobberhood - Tue, 06 Sep 2016 18:07:01 EST 4JPlB6jB No.15191 Reply
This should be {{1,4,7},{2,5,8},{3,6,9}} obviously.
Nathaniel Fembledatch - Wed, 07 Sep 2016 18:46:55 EST DsqbErs4 No.15193 Reply

Oh I misread the OP, you're right. What I mean by manually defining an equivalence is to identify all the elements of one of partition sets. You could rephrase what I said by identifying the orbits of the action of adding 3 to elements of the set, with the caveat that 9 is in its own equivalence class separate from everyone else.

A Geometry(?) Question

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- Thu, 31 Mar 2016 20:43:14 EST Z131bdYa No.15075
File: 1459471394809.jpg -(163021B / 159.20KB, 1294x1294) Thumbnail displayed, click image for full size. A Geometry(?) Question
What is the mathematical/geometric name for the shape of a peanut butter cup like this?

The best I can come up with is "crennelated truncated cone" but I feel like there's some ten-word name I could use that would very accurately describe it....
6 posts and 2 images omitted. Click View Thread to read.
Molly Suvingham - Tue, 19 Apr 2016 21:39:48 EST dFkJK1jc No.15096 Reply
should call it the Reese Cup. if anyone's qualified to name it it's us

Probability question (probably beneath most you)

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- Mon, 16 Nov 2015 07:50:43 EST TdrCDJzk No.14973
File: 1447678243079.jpg -(60015B / 58.61KB, 780x438) Thumbnail displayed, click image for full size. Probability question (probably beneath most you)
I'd appreciate it if someone could answer a probability question for me. I can't remember exactly how to work it out.

Question: How many combinations of 3As and 5Bs are there? For example, one combination would be: 'AAABBBBB' ; another would be 'ABABABBB'.
3 posts omitted. Click View Thread to read.
Lillian Povingstone - Tue, 17 Nov 2015 01:03:27 EST TdrCDJzk No.14977 Reply
Okay. Ignore this thread. I found an online combinations calculator.

Help me help someone get a math-boner

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- Fri, 22 Apr 2016 13:02:27 EST WD6PkLOh No.15100
File: 1461344547382.jpg -(15163B / 14.81KB, 281x180) Thumbnail displayed, click image for full size. Help me help someone get a math-boner
Ok, so how would you introduce someone to the fun bits of mathematics? My girlfriend has maths at standard grade (8/9th grade for Americans I think), and she's interested in seeing why I do it just for fun. She isn't too patient with it, I tried to explain that x^1/3 is the cube root of x and she just got angry after a while and quit, so it needs to have the most 'wow' for the least amount of difficulty (basically math porn). I was going to show her some very basic calculus and some quadratic equation shit, but I'm doubting myself now.
What should I be showing her, or is it a lost cause?
13 posts and 5 images omitted. Click View Thread to read.
Martin Goodfoot - Sun, 17 Jul 2016 21:20:51 EST 9K7KtQWq No.15177 Reply
explain what she enjoys in terms of math. Whenever I tell people you can explain biology/taxes/cooking in terms of math they get intrigued.
George Gennerstock - Mon, 01 Aug 2016 12:05:29 EST yxQzbAra No.15178 Reply
1470067529481.gif -(1562229B / 1.49MB, 340x242) Thumbnail displayed, click image for full size.
I have the same problem. I can't seem to be all that interested in mathematics. The only thing that serves as a motivation is when I solve a problem, which I see as moderate to hard, by myself. Too bad I am bad at maths, so that dopamine release doesn't happen a lot. I see the proposal of mixing maths with something you find genuinely interesting being mentioned. The only thing is, I find everything from astronomy and botany to politics and art interesting. I do not have many hobbies, because I usually lose interest in them after a period. I have brewed, planted, and written graffiti, but they never stick for more than a few projects.
How do I get myself interested in the amazing world of mathematics? I really want to be able to do complex equations one day. Is it really nothing else than forcing myself to do a few problems every day? I have the attention span of a pornstar's pubic hair, so I don't think that will work for me.

Riddle your diddle

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- Tue, 05 Apr 2016 18:49:37 EST cTPi6AuQ No.15083
File: 1459896577222.gif -(2565092B / 2.45MB, 300x226) Thumbnail displayed, click image for full size. Riddle your diddle
There's two guys:
If guy #1 borrows 2 dollars from guy #2, they have the same amount.
If guy #2 borrows 2 dollars from guy #1. he has twice the amount of guy #1.
How much money do they have from the start?
3 posts and 1 images omitted. Click View Thread to read.
Phineas Condlenore - Sat, 07 May 2016 17:02:14 EST 3U6ZTH6i No.15114 Reply
Lekta thought Phoebe was serious...

Lekta should be a cop.
Priscilla Pinkinstone - Sat, 16 Jul 2016 01:31:09 EST Tg2WbKCI No.15175 Reply
poor guy skipped reading comprehension class, wait that isn't real, you should still feel bad

Gamedev is great

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- Wed, 04 May 2016 00:31:32 EST 7yI2oiC+ No.15109
File: 1462336292491.jpg -(194802B / 190.24KB, 906x906) Thumbnail displayed, click image for full size. Gamedev is great
it's a great way to see the impact of changes in your model. Of course this applies mostly to folks interested in applied mathematics. But what is "pure" mathematics, but math that hasn't been yet applied? Give me a physical interpretation of the fractional calculus. Better yet, show me it in a Game.

There's also the fact that a lot of gamedevs struggle with some basic maths, mostly stuff regarding linalg, quaternions come up a lot. You could probably help!

Did you know: There's a 420chan amateur gamedev community, >>>/vg/664016

And from a pedagogical pov, who'd bet against gamedev working its way into the classroom? It's the perfect confluence of any applied area you can think of, Fourier series to taxicab metric
Clara Fadgebit - Fri, 20 May 2016 17:24:26 EST WHIrmu8h No.15127 Reply
1463779466259.jpg -(153794B / 150.19KB, 610x261) Thumbnail displayed, click image for full size.
> gamedev in the classroom

It would take the fun out of it eventually if it's forced. My first program was a game and later gamedev had me apply trig. It is still a lot of boring work, too, a lot of pure programming, so to speak, as pure maths is applied to maths.

Planning is required when fleshing out an game from scratch. There could be too much freedom in a project to grade it. Gamification works better if fit to the audience, eg. in a logic puzzle game.
Ian Goodworth - Sat, 11 Jun 2016 17:23:59 EST +Gs8DK3Y No.15159 Reply
True, making games is lots of programming and boring work until you get the interesting math part.

I think programming shaders is a better way of teaching maths https://www.youtube.com/watch?v=0ifChJ0nJfM
And to be honest most maths you will do in gamedev has to do with graphics.
Shitting Crimmerfield - Mon, 20 Jun 2016 01:47:59 EST ZiObD4pn No.15173 Reply
Maybe gamedev isn't that good for applying maths, but I'm pretty sure it's good for making physics simulations.

How do I recover the signs of integrals and derivatives?

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- Sun, 15 May 2016 20:44:52 EST 1eeqYqTy No.15118
File: 1463359492478.png -(46691B / 45.60KB, 787x421) Thumbnail displayed, click image for full size. How do I recover the signs of integrals and derivatives?
I can define derivatives and integrals in terms of the Lebesgue
measure but how do I recover signs?

$$ \left. \left\lvert \frac{\mathrm{d} y}{\mathrm{d} x} \right\rvert \right\rvert_{x = a}=
\lim_{C \rightarrow \left\{a\right\}}\frac{\lambda^*\left( \left\{ y_x \, \vert \, x \in C \right\} \right)}{\lambda^*\left( C \right)} $$

$$ \left\lvert \, \underset{\, \, x \in C}{\int} y \, \mathrm{d} x \right\rvert =
\lambda^* \left( \left\{ \left( x , y_x \right) \, \vert \, x \in C \right\} \right) $$
Martha Pudgestedging - Tue, 14 Jun 2016 12:22:55 EST c7Q4EFJt No.15163 Reply
So there's two ways to do this. The first is to define the integral in terms of the lebesgue measure and use the doublet distribution to define the derivative in terms of an integral transform and the second is to define a delta as the lebesgue measure of the increasing sections of a function minus the measure of the decreasing sections of a function and then define the derivative using the delta as normal.

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