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11:00 PM
Hello @Huy !! Are you familiar with PDE's??
 
Huy
@MaryStar: I know some PDEs but I'm not an expert.
 
It has drive integration (naturally), 1TB storage space for 2 years with the chromebook. There seems to be local storage - I have files that seem to be saved locally, that I have accessed without an internet connection, that load immediately - but I'm not sure about the technicalities.
 
Huy
Ok. It's one of the cheapest options, afaik, right?
 
I am looking at the energy method applied at this math.stackexchange.com/questions/1205836/… . I have an answer about how to apply this method but I don't know how to conclude that $u=0$. Do you maybe have an idea?? @Huy
 
Yeah
Mine was $250
 
Huy
11:03 PM
No, sorry, @MaryStar.
@MikeMiller: I recently got an iPad Air from my school. But I hate the Apple keyboard layout.
 
Ok... No problem... @Huy
 
Huy
That's what's making me hesitate to get some MacBook
 
Hello @CarlMummert !! Are you familiar with PDE's??
 
@Huy: The one I got is the Toshiba 2, if that helps. I'm very happy with it.
 
I am not very familiar with PDEs, sorry.
 
11:05 PM
How're you, @Carl?
 
I'm doing fine - how are you?
 
Huy
@MikeMiller: I'll have a look at it. I doubt I'll buy a laptop replacement before 2016 anyways. But it's always good to know what's on the market.
Alright, off to bed. Need to go to work in 8 hours. Have a nice evening, everyone!
 
Could you though take a look at http://math.stackexchange.com/questions/1205836/how-could-we-find-the-energy/1206110?noredirect=1#comment2454114_1206110 . I have an answer about how to apply the energy metho but I don't know how to conclude that $u=0$. Do you maybe have an idea??


Here is an other example of the energy method: http://math.stackexchange.com/questions/1199161/energy-method-to-show-uniqueness-of-solution-of-pde

@CarlMummert
 
I'm sorry, that type of thing is not my strength. @Mary Star
 
Ok... No problem... @CarlMummert
 
11:17 PM
When philosophy is guided by mathematics, we get a pedagogically useful oversimplification of mathematics. When mathematics is guided by philosophy, we just get a stifled, bastardized version of mathematics. Let mathematicians lead the way, and philosophers follow after.
 
hi guys
 
hi I'm stuck on a question =(
 
I just want somebody to make sure I don't have logical error in my argument
for some question in set theory
could I ask the question here?
 
I just read in a book a theorem where if you have $k$ vector fields that have vanishing lie bracket in a neighborhood then there's a chart s.t. all of them are partial derivatives. The analogy with simultaneously diagonalizable operators seems very strong to me. is there a deeper connection here?
 
yeah.... depends on how easy...or hard it is
I have studied set theory but only easy stuff
 
11:27 PM
The notions “upper bound”, ”lower bound”, “least”, and “greatest” make sense
whenever we have an order, not just for numbers. Consider a fixed set X and its
subsets. We define an order by saying that A is less than B if A ⊂ B. a) every Y subset P(x) is bounded above and bounded below.
so
Y <= X
and phi <= Y
hence it will be always bounded above and below
what do you think @usukidoll
 
@karim you might as well ask
 
what do you think @CarlMummert
 
uhhhhh.........
Hides
 
yes, because the powerset has a minimum element and a maximum element under that ordering. But it is not common to talk about a single element being bounded above or below, it is more common to talk about a set of elements being bounded above or below.
 
@CarlMummert Hey Carl, could you help me with what i asked?
 
11:30 PM
yeh
 
unfortunately, I can't @saal. but you could ask it on the main site
 
thanks
 
Hello @quid @robjohn @ThomasKlimpel !!

I am looking at this http://math.stackexchange.com/questions/1205836/how-could-we-find-the-energy . I have an answer about how to apply the method. Now I got stuck how to show that $\partial_{t} E(t) \leq 0$.
($\partial_{t} E(t)$ is defined in the answer of the post)

Do you maybe have an idea??
 
@CarlMummert under that ordering can we have an element of the power set such that it doesn't have a maximum or a minimum ?
 
no, like you said the empty set is always the minimum and the entire set X is always the maximum.
 
11:33 PM
oh hell my latex chatjax died :O
 
I see
 
@MaryStar I have no idea what the "energy method" you are using says. You say you want to apply the formula for the energy to a given set of equations, but it is not clear what you are trying to show.
@usukidoll Yeah, the mathjax server has been under a DDoS attack and they are having trouble getting out from under it.
 
so the sup of each y subset of X is just Y itself right?
 
NOOO!
 
11:37 PM
Hello @MaryStar Sorry I have no idea.
 
@Karim the least upper bound of a collection will be the union of all the sets in the collection - you can prove that by showing the union is an upper bound, and is a subset of every other upper bound.
 
Here is an other example of the energy method: http://math.stackexchange.com/questions/1199161/energy-method-to-show-uniqueness-of-solution-of-pde

At the anwer there is the energy given by the formula $$E(t) = \frac{1}{2} \int_{a}^{b} u_{t}^{2} \, dx$$

Then the derivative is:
$$\partial_{t} E(t) = \frac{1}{2} \left[ u_{t}^{2}(b,t) - u_{t}^{2}(a,t) \right]$$

we want to show that $\partial_{t} E(t) \leq 0$ so that we can conclude that $u=0$. But how could we do that?? @robjohn
 
@MaryStar That would only be true if $u_t^2(b,t)\le u_t^2(a,t)$
 
yeh I see
and I guess the greatest upper bound will be the intersection
 
lower?
 
11:42 PM
@Carl
@CarlMummert *
 
right, the greatest lower bound is the intersection
 
But this is not known since $u$ is the function that we are looking for, or not?? @robjohn
 
also @carl works by itself
 
alright good :D
 
11:43 PM
@MaryStar I don't know what you are looking for.
 
thank you @carl
 
@MaryStar You either need to give more background in your question as to what the energy method is and what it is trying to solve, or ask your instructor, as they hopefully knows the background.
@MaryStar Your question consists of a stream of equations and inequalities from your notes and a formula for the energy. I have no idea where to take that.
 
I will add more information at the post and sent it to you. @robjohn
 
11:57 PM
0
Q: Lie derivative and simultaneous diagonalizability?

Saal HardaliI just arrived at this theorem: Let $M$ be an $n$-manifold and let $\{X_j\}_{j\le k}$ be a collecion of $k$ vector fields satisfying: 1) $\{X_j(q)\}_{j\le k}$ is linearly independent 2) $[X_j,X_i]_a = 0$ for all $a$ in some neighborhood $V$ of $p$. $\implies$ There exists a...

 
@robjohn http://i.stack.imgur.com/MaKfP.jpg

on 2c I need to rewrite the model in terms of the rescaled version
so it already gives me the subsitutions
X_t = B_t/k, b = ac, and Y_t = E_k/ka
so I need (x_t)(k) = b_t, and Y_t(ak)= E_t and put it inside these equations B_{t+1}=e^{-cE_t/B_t} and $E_{t+1} = aB_t

right?

So my new equations are

Y_{t+1} = X_t and X_{t+1} = 1/K e^{-bY_t/X_t}
 

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