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/sci/ - Science & Math

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4155296 No.4155296 [Reply] [Original]

>learning how to optimize a function
>teacher uses simple arithmetic method that has no intuitive basis behind it, works in some cases, not all

>decide to use lagrange multiplier method on exam
>show all my work, get the right answer
> -2 marks because I didn't use his stupid method

>> No.4155299

>>4155296
Should have gotten a fucking 0 for overcomplicating things you fucking douchebag.

>> No.4155301

6th grader detected

>> No.4155319

I don't know what any of this is.

BRB in high school calculus.

U irate?

>> No.4155325

>>4155319
>>4155301
>>4155299
oh posters of /sci/, why are you so low quality?

>> No.4155328

>>4155319

yes I irate.
its not a math course, its biology and we just had to find maximum amount of pressure in a blood cell given by a function

>> No.4155338

>its not a math course, its biology

Awesome way to look like a total elitist douchebag you fucking retard.

Oh, ohh you know how to use Lagrangian multipliers, congrats welcome to sophmore math level.

>> No.4155342

I feel you OP

>> No.4155353

Knowing Lagrange multipliers is nice and all, but if your teacher was able to use simple arithmetic to solve the problem, then I'm pretty sure Lagrange multipliers would just make more work for such a simple exercise.

>> No.4155354

Did this fucking faggot really expect sympathy here? I think any teacher who has to deal with this cuntface should be allowed to punch him in the area usually reserved for the male reproductive organ.

>> No.4155363
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4155363

>>4155354
>I think any teacher who has to deal with this cuntface should be allowed to punch him in the area usually reserved for the male reproductive organ.
how's that autism treating you.

but anyways, shit like that is a symptom of our failing education system. All its goals and priorities are misplaced and disproportionately emphasized.

>> No.4155374 [DELETED] 

Piss off nigger bits

>> No.4155377

>>4155363
Hur hur, being practical is also part of education you fucking asshole.

If you are using LM for something that can be solved by simple arithmetic then you are doing it wrong.

Don't blame the education system just because you want to be celebrated for being a complete douche. Sure you learn your unnecessary multipliers while everyone was socializing and obtaining more important skills than something a fucking computer can do in 2 seconds.

Enjoy being autistic an a failure.

>> No.4155382

>>4155353

the mechanics are simple but it changes depending on each question so basically we are forced to memorize a bunch of different forms,.....its silly

or i can use one form that makes sense and I know how to manipulate

>> No.4155383

I remember a lecturer getting pissy because I simplified some exponents.

Her argument was "if it's not 3*10^8m/s, it's not the speed of light", she genuinely did not understand that (x*10^8)/(y*10^5) simplifies to (x*10^3/y).

She didn't care that the answer was correct.

>> No.4155385

>>4155363
No, the point is not to solve the trivial problem, the point is to gain the skills to solve them, usually as fast and simply as possible. Therefore you should not overcomplicate problems just to inflate your own ego.

>> No.4155391

>>4155377
>backinmydaytrollingmeantsomething.jpg
I hope you're not honestly flipping a shit over the extra 2 minutes needed to do the langrange multiplier method. I mean, you've already spent more extra effort making posts that make you look like an adolescent.
must be winterbreakfags in /sci/ today. I don't expect much out of this board but today is really a humdinger

>> No.4155398

>>4155383
you have to not be an asshole and understand that lecturers are not omniscient, and in the case that one may not be aware of something that you are, it's not helpful to present the information in a way that will "show them up" and make them look bad in front of the rest of the class.
This isn't a flaw.

>> No.4155403

>>4155398

Knowing basic algebra is not omniscience.

>> No.4155410

>biology
Dude, seriously? You KNOW that your teacher isn't going to understand basic calculus, yet you used Lagrange Multipliers?

>> No.4155413

>>4155383
Maybe she meant that it was more informative in her form since you could read the components of the number?

>> No.4155416

>>4155391
I find joy putting assholes like yourself in place. In fact, I'm doing you a favor. You come here with this "why everyone is so dumb, the system can't deal with my genius" type of attitude, when everyone thinks you are just a complete dumbass.

Its not just that it takes 2 minutes, you are obviously trying to brag and make it a big deal otherwise you wouldn't create a thread complaining about it.

>> No.4155427

>>4155416
And the extra 2 minutes probably doubles the time needed for the problem.
I guess sci is where teens come to try and stroke their egos.

>> No.4155435

>>4155427
>everyone is wrong except me, so I'm just going to keep my shitty attitude.

suit yourself

>> No.4155436

>>4155382
>>4155382

this makes sense, OP is right

>> No.4155439

>>4155427
>>4155416
I'm not even OP.
You are THIS mad about absolutely nothing.
Do /sci/ a favor and stop posting

>> No.4155448

>>4155435
Lulz, I just agreed with that poster I was referring to so obviously there is at least one other person than me who's not wrong, I think you should just go to the toilet and drain your anus of the jizz. Anyone who thinks OP is a freedom fighter is the one with the shitty attitude, you faggots should be happy anyone is wasting their time on you.

>> No.4155495

>>4155448

you say "be complacent!"

op says "fight the power!"

>> No.4155522

>>4155495
I'm saying that on rare occasions the teacher actually has something to teach so shut the fuck up, open your ears and stop pretending you know everything already.

>> No.4155532

>>4155522

except not in this situation

he taught an ad hoc method that works sometimes and only in specific ways and it makes no intuitive sense

its like teaching how to take a derivative in some random way that isn't actually a method but its simple and stupid

no thanks

>> No.4155536

>>4155532
I don't know the specifics so all I can assume is that the teacher is right and this angsty teen is wrong.

>> No.4155540

I helped my roommate with her college algebra homework and they were doing stuff with polynomials.

I taught her the quadratic formula because it made more sense to her and she got her entire homework marked incorrect (the answers were right).

Who the fuck cares whether you factor or use the formula, it's college algebra these kids will be taking calculus at the most.

>> No.4155546

>>4155540
Because you need to understand the formula before you use it.

>> No.4155556

>>4155546

I disagree, these aren't math or science majors, these are business majors that are required to take these classes. The understanding adds nothing to their educational experience.

>> No.4155557

>>4155536
Whenever anyone says "angsty teen" on the internet it's a sure sign that they're an enormous twat. You've shown much more immature angst than anyone else in this thread

>> No.4155566

>>4155557
Hahaha, talking about ad hominem, good stuff bro, best laugh I've had in the entire thread.

>> No.4155572

>I'm a free spirit that needs to be encouraged every time I do something unique.

This is how stupid you sound OP

You get -2 for being unpractical, I don't see any problem with that. If your solution was easier than simple arithmetic then i would support you (i would think you are dick anyway tho)

>> No.4155576

>>4155566

hes right tho

>> No.4155582

>>4155572

so you prefer a method that only works half the time and has no logic behind it

ok

>> No.4155585

>>4155576
That's exactly the picture that OP paints in his post though.

>> No.4155589

Are Lagrange multipliers supposed to impress us? Sounds like you used a pointless elaborate tool. What was the exact problem?

>> No.4155602

>>4155585
what because of the picture?
is your sense of humor broken?

>> No.4155606

I bet you'll be that faggot who evaluates Bromwich integrals instead of just remembering a few common Laplace transforms.

>> No.4155608

>>4155589

>impress us?
>elaborate tool

no they aren't elaborate. they make sense and are easy to apply assuming the function isn't crazy.

his method wasn't a method, it was an algorithm that just happened to work by substitution and setting shit equal to each other but if you ran into an x^2 or x*y it wouldn't work....i didn't bother to learn it because it was useless, it was taught because he assumed no one in biology knows calculus

>> No.4155609

Regardless if the OP wanted to look cool/like a faggot. He got the correct answer using a legitimate method, I would take it with the dean, if you really were pissed about it.

Also lol @ thinking a biology professor knows what a lagrange multiplier is/

>> No.4155616

>>4155609
> Also lol @ thinking a biology professor knows what a lagrange multiplier is


His T.A probably got confused

>> No.4155620

Why would anyone get mad at OP for finding the right answer? Polite sage because the thread is full of flaming faggots.

>> No.4155621

>>4155602
I'm not talking literally, the picture is painted with the words he uses.

>> No.4155625

>>4155582
>arithmetic
>no logic

Seriously..

If you were going to solve a set of optimization problems your solution would probably make sense, but that wasn't the case.

Fact is, some dumbass that never took a college math class solve the problem faster than you.

>> No.4155627

>>4155608

Ok, so what was the actual problem. Can you remember it?

If it has xy terms then I suppose it may be worth using Lagrange multipliers. I was thinking it was a simple function of one variable.

>> No.4155630

>>HURR DURRR YOUR JUST SHOWING OFF

I can't believe I'm defending OP but the stupidity in this thread is staggering. Using an optimization method that works instead of one that doesn't isn't "showing off". It's giving the correct answer. Assuming that he's showing off because he's using a more advanced method is stupid. Taking off points for the ***correct answer*** because he's "showing off" is even more stupid.

Also I agree with
>>4155609
Take it to the teacher or to the dean if the teacher refuses (and you care that much about 2 points).

>> No.4155633

>>4155620
>>4155609
>>4155608
>>4155582
>>4155576

so much samefag

>> No.4155638

The grad student who graded your shit probably has never even seen LM before. They probably thought you bullshitted something and guessed the right answer.

>> No.4155641

>>4155630
They took points because he was being unpractical and waste some precious time to the T.A

>> No.4155647

>>4155633
>some others reading this thread support OP
>HURR DURR SAMEFAG

>> No.4155660

>>4155633

nope...I'm not any of those guys


The situation the OP is describing is that the prof is teaching
to solve

e^x = cos x, you just keeping guessing what x is

where as OP is actually trying to use a method to solve the transcendental equation.

>> No.4155663

The smart thing would have been to ask the prof if it's okay to use Lagrange multipliers instead of his method. Yes it sounds stupid to do so, but it's time to get used to the fact that you are in the university system, and sometimes you'll have to deal with bullshit from your superiors.

>> No.4155664

>TA looks at work, sees lambdas and partial deriatives
>sees correct answer
> -2 marks

LMFAO

>> No.4155673

>>4155641
There is *nothing* unpractical about using an optimization method that always works instead of one that sometimes fails. And the Lagrange multiplier method probably took like at most 10 lines of equations. Taking points off for something like that is insane.

Have you ever graded exams as I TA? If I told my professor that I took points off for a student using Lagrange multipliers because he was wasting my precious time, he'd rip me a new one.

>> No.4155686

>>4155673
As someone who has been a TA, I'm impressed when people use methods not taught in class to correctly solve problems. It shows that they really understood what they had learned elsewhere since they can apply it in a different context.

>> No.4155692

>>4155641
Go be a fucking T.A. sometime. There are bad seeds, but there are also a lot of well meaning people who work 10 hours and get paid for 5.

>> No.4155698

LM is fucking simple as fuck. It turns maximization relative to a constraint into a system of algebraic equations. Anyone saying "oh boo hoo, you should use the shitty half-assed backwards constraint solving method of the teacher, which will end up ADDING complexity to a simple problem" is full of fuck. Practicing LM is fine. Tell the teacher he's an asshole after you're out of the class. Tell it to his face.

>> No.4155700

>>4155673
Its a bio course. The problem that OP was solved must be trivial.

I doubt the TA had any math background, plus some general bio courses have HUNDREDS of fucking students. 10 lines of equations might not sound like a big deal but for them it might be.

>> No.4155709

>>4155698
Typical nerd elitism.

Stay virgin man

>> No.4155723

>>4155700
+ he might have had to contact the professor or something just to give him some points for it instead of just doing it like the course taught it.

>> No.4155733

>>4155403
Look, I'm not arguing with OP or whatever but you're just a faggot. Calling teachers out on their mistakes is just being a smartass douche and nobody likes a smartass douche. People do silly mistakes, that's normal. Most of the time they notice their own mistakes and correct them before you ever notice there's something wrong. Have some humility for fuck's sake, don't be a pretentious asshole.

>> No.4155739

Jesus fucking Christ...

Check it out OP, your instructor was being a dick. His reaction to your answer can be simplified like this: it made him uncomfortable.

The conventional method of teaching is usually just rote and lacks any kind of conceptual understanding, nor can it be readily applied in complex situations. It indicates that the instructor might lack a deeper understading of the work. And every wanna-be asshole here that said something along the lines of "but OP was just being an elitist fuck-tard!" are stuck in the same rut as the instructor. They don't WANT to understand, thay want to stick with rote answers because that's what they are comfortable with.

Keep up the work, OP. Don't let these dicks discourage you. Keep using your brain.

>> No.4155747

>>4155739
5 star post

>> No.4155753
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4155753

>>4155739
>Keep up the work, OP. Don't let these dicks discourage you. Keep using your brain

th...thanks

>> No.4155771

>>4155739
No, I don't like to be shown anything without having it proven soon afterwards so I do want to understand but this douchebag OP should just use the methods of the course and then when he does his own research he can use whatever methods he wants.

>> No.4155785

>>4155771

I'm calling bullshit. If we all "stuck to the course" we'd all be copying the fucking Volgate in a monastary instead of modern science.

Guess what? Critical thinking is NOT something to be punished.

>> No.4155817

>>4155771

durrr rote memorization is best, stick to the plan, don't upset teacher, dont do anything imaginative

are you chinese?

>> No.4155819

>>4155785
It doesn't really sound like critical thinking, it sounds like complete overkill. And it's not like he's doing anything revolutionary so that dramatical scene really isn't really relevant to our discussion.
OPs post basically adds up to him saying, ''I'm smart, smarter than my teacher, love me''.

>> No.4155841

>>4155819

> not like he's doing anything revolutionary
Then there shouldn't have been a problem.

>> No.4155880

>>4155841
You are proposing it only be a problem if he's doing something revolutionary? Is this some kind of joke? He's wasting time and energy, not only his own, for no reason.
Saging since the thread is finally circling the drain.

>> No.4155883

>>4155664
This. REALLY. It is most like exactly this.

Instead of raging about it why not DO something about it? I'm sure if you went to your TA and said... herpa derp LM here why did you minus 2 the TA would most likely just give you full marks.

Seriously... I don't understand why people worry so much.

> Fun fact: I am a TA for calc and hate when LM come up. So much fckin work.

>> No.4155898

>>4155883

too late bro, I already got my final mark so...and -2 marks on a mid-term won't change my final anyways

I'm just mad at the principle of it.

>> No.4155946

>>4155898
You are getting mad at something insignificant.

This is a total waste. Try optimizing your life by not worrying about things you can't change.

>> No.4155978

>>4155946
all of you people hating on OP have spent so much time and energy because of the principle of the discussion and you can't change the way me and the OP see things.
You're just grasping at straws now to make yourself look right.

>>4155880
It started circling the drain as soon as everyone started being all "don't rock the boat"

>> No.4155979

I had something similar happen, but it was in College Algebra. We were learning to find the vertex of the function using Algebra, and instead of the clusterfuck of using Algebra to find it, I just took the derivative. I didn't lose points, but the teacher suggested that I was in the wrong class.

>> No.4156003

>>4155978
It was never about rocking the boat, it was about him being a faggot.

>> No.4156019

wolframalpha compansates all the math needs i have now or will have

people should just write those programs and forget their origins completely for future generations

>> No.4156023

>>4156019
2nded. Educating people on what can just be done by computers is wasteful and stifling to the economy.

>> No.4156111

>>4155819

Actually Lagrange multipliers are the easy option once you're familiar with them.

>> No.4156139
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4156139

posting in a troll thread

>> No.4157202

>>4156111
This is the truth. It used to be I'd solve a problem like "You want to enclose a rectangular field adjoining a straight river with 400 yds of fence; how do you maximize the area?"
So you go through this process of finding the function, xy, for the area, then you subject it to x+2y = 400. This is where the methods differ. Instead of just adding and taking the partial derivative, you don't even try. You do variable substitution. Then you have (400 - x)*x. This wasn't really any easier than solving x + 2*lambda = 0, y + lambda = 0; x + 2y = 400, unless you're so bad at calculus you decided to go into biol-

Shit. OP, I forgot how terrible biologists are. I've never had one accept critical thinking from me before.

>> No.4157214

>>4156023
>2011
>thinking the post above you was in earnest

>> No.4157234

>>4155296

>> Not using the simplest method to solve a problem

That's a fucking F around here. Complexity is a bitch when you move beyond your child play.

>> No.4157251

>using Lagrange multipliers instead of reformulating the problem as a variational principle and using Euler-Lagrange equations

>> No.4157255

Unless the question specified you had to use his method then I would give you full marks

>> No.4157258
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4157258

I love what my econ teacher told me to do in order to find some number for some shit.

"Just divide the number by 72"

He couldn't say why

>> No.4157260

Unless the the question specifically said "using the method of _______, optimise hte function blah blah" OP should get full makrs using whatever valid mathematical method he wants.

using lagrange multipliers might well have been slower than the intuitive, method of inspection it souns like the teacher used, but it shouldn't be penalised. I'm not sure why posters like >>4155338>>4155299>>4155354
feel so vindictive.

>> No.4157299

I'm a TA in a population genetics course.
One of the exercises was to calculate allele frequencies (for a two allele locus) that maximize the frequency of heterozygotes.
One of the students solved it by using Lagrange multiplier method. If I was not forced to do otherwise by the prof, I would have deducted points for not realizing that allele frequencies are not independent (they sum up to one).
So you see, even though he knows how to use L. multipliers, he still fails at understanding the most fundamental thing in population genetics: Hardy-Weinberg equilibrium.

>> No.4157328

As a mathematics grad student I fail to see the problem with what OP did. Unless of course he applied Lagrange multipliers wrongly or something more was to be gained from the professors method, in which case we aren't given the full story. But in general I would agree to using a theoretically underpinned method over some homebaked special shit from someone who doesn't even deal with mathematics day in day out.
But I do have the suspicion that OP is not telling the whole story. On the other hand it sounds like high school and thus I could even relate, some teachers really didn't have their shit together back then...

>> No.4157329

>>4157258
http://en.wikipedia.org/wiki/Rule_of_72
Mystery solved. Also prof confirmed for full retard.

>> No.4157357

>>4157329
That's the dumbest shit I've ever seen. Econ cannot into maths

>> No.4157369

>>4157258
Rule of 72 is the shit. Seriously, I love that thing.

>> No.4157377

>>4157357
You're not okay with ln(2) ~ 0.72, ln(1+r) ~ r for small r, ln(2)/ln(1+r) ~ 0.72/r, for small r? You mean, you're not okay with a rule like this for when you're in a brainstorming session, trying to figure out ideas, and you don't want to look retarded whipping out of the calculator and doing the old "log of two ... divided by ... shit, 1 + ... r ... log ... add to memory ... 2, log, divided by memory equals ..."
The rule of 72 works because 72 is an approximation to 100*ln(2) and the percentage is an approximation to ln(1+r). Shit is FANTASTIC.

>> No.4157378

So /sci/ recommends using a method that doesn't always work to solve a problem instead of a more complicated method that will give the right answer just because it's easier? Sure smells of biofaggotry up in here.

>> No.4157379

>>4157377
>his calculator uses memory stacks instead of simply typing out expressions

I bet your computer uses Polish notation.

>> No.4157381

>>4157377
I take it that you are very good at dividing by 72 then. I'm not and would need a calculator, or write shit down in any case.

>> No.4157382

>>4157377
>72 is an approximation to 100*ln(2)

Other than the fact that ln(2) ~ 0.69, right?

>> No.4157383

>>4157377
>72 as an approximation to 69.3147...

>> No.4157385

>>4157381
Nvm, I misunderstood

>> No.4157386

>>4157382
>>4157383
>hivemind.jpg

>> No.4157387

>>4157382
>>4157383
>implying anyone other than engineers would use a rule of 69

>> No.4157389

>>4157379
Actually, I was joking about pocket calculators, and not scientific calculators. My calculator is a parser I wrote one day when I was bored that uses a hand-coded LL(*) parser, in reverse direction, to construct an expression tree, and then evaluates that tree recursively in post-order fashion.

>> No.4157393

72 is an approximation for 8(ln 2)/(ln 1.08), so go suck on some balls. It's not used for high-accuracy approximation. 72 works reasonably well for most interest rates.

>> No.4157394

>>4157387
And frat boys, but that's probably a different "Rule of 69"

>> No.4157396

>>4157378

You are a HUGE faggot.

>>Implying using derivative laws isn't easier, quicker, and simpler than using the definition of derivatives in every case of derivation

>> No.4157406

>>4157396
Derivative laws will always work for any known set of functions, and Lagrange multipliers are not nitty-gritty like definition of limit is.

>> No.4157428

>>4157396
>missing the point

Applying derivative laws will always give the correct answer. Perhaps you should read the OP again?

>> No.4157515

I was one third through this thread before I realized that everyone is retarded.

False Dichotomy, look it up you mediocre plant fuckers.

>> No.4157538

>>4155296
So, you can't follow simple instructions, and you're mad?

>> No.4157544

>>4155296
OP, did you ever consider that your teacher was testing whether you knew how to do the arithmetic mathod, and not what the fucking answer is to an arbitrary problem?

Man, wtf do people think testing and learning is about?

>> No.4157947

>>4157544
Learning and testing are two completely different things. Tests on the whole are artificial and serve no real world purpose; the fact that OP arrived at the correct answer and was not awarded the marks is proof of that.

>> No.4157964

>>4157544

why would he? it was a bio course not math. His method isn't a method its a gimmick that works sometimes, and it's intended for people who haven't taken calculus/linear algebra...