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Anonymous
8:00 PM
@BalarkaSen I'm trying to prove $\alpha \beta \leq \frac{\alpha^p}{p}+\frac{\beta^p}{q}$ where $\alpha,\beta \in \Bbb R^{+}$, $p$ is $1$ and $q$ is given by $\frac{1}{p}+\frac{1}{q}=1$. I'm trying to find some non-calculus way for this
 
I can AM-GM it for integral p, q
 
Anonymous
$p$ and $q$ are not integral though
 
Anonymous
I mean may not be
 
@bolbteppa Well that's not the full story, because the notation $(n_1,n_2)$ refers to a representation.
 
Not in general, you mean.
 
Anonymous
8:01 PM
Yes
 
I keep forgetting that identity from my short term memory, but a non-calculus way of looking at it is that it's expressing the concavity of the logarithm
 
@Blue There's probably subtleties in general. You have to prove for rational $p, q$'s, which should be only slightly harder
Then by density of rationals extend that to $p, q \in \Bbb R$
 
Anonymous
Anyhow, I might try using calculus too
 
Anonymous
I need to construct some function probably
 
@bolbteppa I think it's the Holder inequality
@Blue Yeah simplest is to prove it using Lagrange mutipliers
 
8:03 PM
This is Young's inequality which you use to prove Holder's inequality right
 
Oh yes sorry
 
Anonymous
Yeah, I was trying to prove Holder's inequality
 
Anonymous
Let's see: Lagrange!
 
I forget names
 
Anonymous
The constraint is: $\frac{1}{p}+\frac{1}{q}=1$
 
Anonymous
8:05 PM
I need to minimize: $\frac{\alpha^p}{p}+\frac{\beta^p}{q}$
 
Anonymous
Or maximize:
 
Anonymous
$\alpha \beta$
 
2
A: Concavity of log function for proof of Young's Inequality

vrugtehagelSo the logarithm is a concave function, as its derivative $\frac1x$ is strictly decreasing. A property of concave functions $f(x)$ is the following: Say you have two points, $x<y$. Then, if $0<a<1$, we know that $(1-a)x+ay$ is a number between $x$ and $y$. Thus, for concave functions, if we dr...

Of course calculus lets you prove the log is concave quick enough
and the whole 1/p, 1/q business is magic from this perspective
 
Anonymous
@bolbteppa Hmm, interesting. Reading through that!
 
the integral proof is another way of seeing the 1/p, 1/q stuff more naturally, and the picture is cool
 
Anonymous
8:07 PM
The integral proof looks like complete trickery to me. So was trying to avoid it
 
I agree, but if you do it the other way the p's and 1/p's are trickery
 
@Blue Do this
 
I know another proof which is too crazy to try to remember the details of
 
@Blue Am Gm,
and then derive holders from it
 
@PrathyushPoduval Only works for integral $p, q$
 
8:11 PM
@davidphysics yes everything I have read is indeed very hand-wavey talking about this, not clearly explaining how it is a representation, just stating it
 
But it can be made to work for rational $p, q$ like I said, and you'd prove the full thing from it
 
@BalarkaSen no it needdt
I think am gm extends for genreal t and 1-t
 
Anonymous
$\alpha^{p}(p\log(\alpha)-1)/p^2=\lambda (-1/p^2) $ and $\beta^{q}(q\log(\beta)-1)/q^2=\lambda (-1/q^2)$
 
@PrathyushPoduval Sure, same as my suggestion
 
ah yeas
 
8:13 PM
But good to know that works
 
@Blue Why are you differentiating wrt $p$ and $q$? That's not what you want to maximize...
You have fixed $p$ and $q$
 
Anonymous
I'm confused
 
Anonymous
One sec
 
You want to maximize $f(\alpha, \beta) = \alpha^p/p + \beta^q/q$
 
8:17 PM
Just like $0 \leq (a - b)^2 = a^2 + b^2 - 2ab \to ab \leq \frac{1}{2}a^2 + \frac{1}{2}b^2$ you can write Young as a generalization $ab \leq \frac{p-1}{p} a^{p/(p-1)} + \frac{1}{p} b^p$
 
use jensens inequality
@Blue^
 
It's too arbitrary to add in these $(p-1)/p$ terms :(
 
Anonymous
@BalarkaSen If I partial differentiate the constraint with $\alpha$, $\beta$ that becomes $0$.
 
Anonymous
@BalarkaSen Also, I want to minimize that thing
 
Anonymous
Not maximize
 
8:21 PM
do you want a calculus methos>
?
 
Anonymous
@PrathyushPoduval I'm trying to use Lagrange multipliers
 
okay lets see
1) there are no constrains on your variables
 
@Blue You wouldn't get that
$1/p + 1/q = 1$ is not a constraint on $\alpha, \beta$
@PrathyushPoduval You have to set up one
 
Anonymous
@BalarkaSen I agree. Then what is the is the constraint you're using for LM
 
Try $\alpha \beta = C$
 
8:25 PM
yes
 
Anonymous
I was trying to show that for a given $\alpha,\beta$ the minimum value of $\frac{\alpha^p}{p}+\frac{\beta^{q}}{q}$ is $\alpha\beta$, the constraint being $1/p+1/q=1$
 
That's not a constraint.
It's a condition on $p$ and $q$.
 
Anonymous
What's the difference between constraint and condition? I don't see. Anyhow, yeah in general I agree $\alpha, \beta$ is not fixed
 
Anonymous
I'm trying it your way
 
A constraint is a condition on the variables when you're extremizing something
 
Anonymous
8:30 PM
$(a^{p-1})=\lambda b$
 
Anonymous
$(b^{q-1})=\lambda a$
 
Eh, it's a constraint on the parameters defining the problem instead of on independent variables.
 
Anonymous
So yeah, it minimizes when $a^{p}=b^{q}$
 
Anonymous
But, it's minimum value is $ab$ iff $1/p+1/q=1$
 
Anonymous
@Semiclassical Could you be a bit more clear?
 
Anonymous
8:38 PM
I couldn't understand
 
Anonymous
"it's a"
 
Anonymous
What is "it"?
 
The condition "1/p+1/q=1".
 
I'm saying that the only real difference between 'condition' and 'constraint' here is that the former applies to the parameters of the problem and the latter to the independent variables of the problem.
 
8:41 PM
From $ab = e^{\ln(ab)}$ you can reduce the problem of analyzing $ab$ to analyzing the convexity of $\ln(x)$ (or $e^x$ if you want), then use the above.
 
@BalarkaSen I have all your movies
 
Wee
 
I'll set up an access server today
 
I wonder if it'll take infinitely long to download on my end
 
Possibly
 
8:47 PM
How big are these lmao
 
@JohnRennie Can you lend me a VM with some 10GB of storage so I can transfer some files to @BalarkaSen without having to leave my laptop on at all times?
@BalarkaSen Totalling some 10GB I think
 
Fucking hell
I suspect this will take days
 
If John can't help I'll set up my raspberry pi as a provider
That's fine
Assuming my internet doesn't die, lol
 
Same!!!
 
We just need to use rsync
Oh wait
You run malware right?
 
8:48 PM
lol
i run windows
 
Sigh
Why dude
top 10 anime betrayals
Let's wait for @JohnRennie's advice, I don't know how to do anything reliable on Windows
Going to shower; brb
 
See ya
 
Anonymous
@BalarkaSen Alright. I understood your method of considering $f(a,b)$ to be the function we are trying to extremize. What if I try to extremize $g(p,q)$ instead? Where $g(p,q)=a^{p}/p+b^{q}/q$
 
my download is like 20 mbps.
 
Anonymous
$a,b$ beings constants this time.
 
8:53 PM
@Blue Not sure what happens
 
Anonymous
I get a feeling that the minimum possible value would be $ab$
 
Anonymous
(if $1/p+1/q=1$)
 
Anonymous
The lagrange equations are a bit complex
 
Anonymous
So the condition for maximization in that case would be $a^p(\log(a^p)-1)=b^{p}(\log(b^p)-1)$
 
Anonymous
$x(\log(x)-1)$ is not a strictly increasing function
 
Anonymous
9:03 PM
If $a^p,b^q>1$ then $a^p(\log(a^p)-1)=b^{p}(\log(b^p)-1)\implies a^p=b^q$ I think
 
Anonymous
Then it is possible to say that the minimum attainable value would be $ab$ for $g(p,q)$
 
Anonymous
$d/dx(x\ln(x)-x)=x(1/x)+\ln(x)-1$
 
Anonymous
$\ln(x)=0$
 
Anonymous
At $x=1$
 
Anonymous
So, okay
 
Anonymous
9:08 PM
So, yeah. The same inequality $ab \leq a^p/p+b^q/q$ (in this case $a,b$ are constants)would also hold if $a^p$ and $b^q$ are greater than $1$. I guess just $a,b>1$ would do
 
9:34 PM
@Blue Are you doing L^p spaces?
 
 
1 hour later…
10:44 PM
@davidphysics Yes, you are correct. But I also think this question is a sufficient duplicate for that - you could add your answer there.
 
10:57 PM
@ACuriousMind Halp
 
11:19 PM
@BernardoMeurer ?
 
@ACuriousMind Ah, I don't remember what I need help with now
@ACuriousMind but please do help me with it
 
11:36 PM
@BernardoMeurer what do you need
 
If you ask a similar variant of the same question multiple times on a site you will get multiple answers from different people who see it in the moment, if you only allow it to be asked once you will get maybe one answer and people wont answer it years later as it looks closed and answered, a policy closing these kinds of questions wrecks the site, and lets it's competitiors e.g. the math version of this, do better
person is talking about thermo and EM here, physics.stackexchange.com/q/372185/25851, linked post physics.stackexchange.com/q/70376/25851 is going on about lagrangians, makes no sense to think this answers it, ridiculous ridiculous policy
 
@0celo7 I already solved all those proofs but now I have a new one
 
@BernardoMeurer what is it
 
@0celo7 It involves geometry, I'm drawing it on a paper
 
ew
 
11:50 PM
I sent it to you on iMessage
it's hideous
I don't even know what it is tbh
 
@BernardoMeurer I don't believe it for the example you drew
 
@0celo7 Me neither
 
there are 8 tiles, which is not div by 3
 
I got it from that picture I sent you yesterday
I'm missing a row of triagles I thinkg
 
maybe, I dunno
the picture cuts off
 
11:53 PM
Ye
If I add another row it's 16 triangles ($4^2$) and if you take the edge of it's 15, which is div. by 3
 
ok
it's some horrible induction proof then
 
Is it not just showing that any $4^n - 1$ is divisible by 3?
 
maybe, but you need to show that it's equivalent to that
 
I guess I need to show that any three conjoined eq. triangles is a trapezoid ?
 
that's not true
 
11:57 PM
Counter example?
 
oh, equilateral
yeah that's true
 
Ye
How do I show that even
 
draw all the combinations
 
Any way to do it analytically?
 
this isn't analysis
 
11:59 PM
;-;
I don't want to draw
I'll say it's trivial
 

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