2,773 reputation
1518
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location Spain , Basque Country , Bilbao
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visits member for 3 years
seen yesterday

i got a degree on Physics and have several ideas on my own , unfortunately i do not have a physics sponsor :) in order to get an investigation grant :)


Mar
23
comment laurent series of a function defined by an integral
$ g(t) $ is smooth with no poles so the integral exists for every 'x' since there are no poles in the integrand
Mar
19
comment Real roots plot of the modified bessel function
OK thanks in fact i managed to prove that the roots of the function (smooth part) was about $ \frac{ \sqrt{E}}{2\pi}log(\frac{\sqrt{E}}{2\pi e}) $ that's why i thought that the zeros would be related
Mar
15
comment A variational problem with a lagrangian , what is the lagrangian?
THANKS a lot could yuou help me with other problems i have about variatonal calculus :D i must prove 20 exercises but i have only solved 4 :D
Feb
26
comment Help in differentiating a complicated function
$D(f(X)g(X))=f'(x)g(x)+f(X)g'(x) $ apply this to your 2 produc t and remeber the minus sign before epsilon
Feb
20
comment minimal surface from a variational problem
i have donwloade the book and in example 8.1.2 they put only the Euler lagrange equation i put in my question they do not explicitly evaluate the mean curvature of the surface
Feb
20
comment minimal surface from a variational problem
of course but i know would need the curvature equation in $ R^{n} $ to see that the vanishing of Euler lagrange equation is the vanishing also from the mean curvature in n-dimension
Feb
20
comment minimal surface from a variational problem
io know i should compare my Euler lagrange equation with the differential equation of the mean curvature am i right ? where could i find more hitns ?
Feb
20
comment minimal surface from a variational problem
i found this problem on Evans partial differential equations chapter 8 books.google.es/books/about/… chapter 8 problem 12 :)
Feb
18
comment A variational problem with a lagrangian , what is the lagrangian?
shouldn't this be the term $ e^{f(x)}$ instead ?= in both cases ??
Feb
18
comment A variational problem with a lagrangian , what is the lagrangian?
thank you RObert :D wehn i have enoguht poitn to vote i will give you a point thanks again
Feb
18
comment Solve $y'(t) = \dfrac{1}{1+ty}$
wolframalpha.com/input/…
Feb
18
comment Solve $y'(t) = \dfrac{1}{1+ty}$
i suggest to define a new function $ u(t)=ty(t) $ to see what happens
Feb
13
comment Find solution for the following system: $x'=y^3-4x$ , $y'=y^3-y-3x$
you know $ y-x=f(t) $ for some function now you should replace this identity inside your equation :D
Feb
13
comment Find solution for the following system: $x'=y^3-4x$ , $y'=y^3-y-3x$
what do you jean by 'invariant' xy is time invariant so $ \frac{d (xy)}{dt }=0 $
Feb
8
comment Can I express $\sqrt{x}$ as $Q(x)$ where Q(x) is a first degree polynomial?
you can use the identity $ (\sqrt x +1)(\sqrt x -1)=x-1 $ to approximate the root by a rational function
Feb
5
comment The Laurent series of the digamma function at the negative integers
but i do not get it if we put $\Psi (x)= \frac{1}{z}-\gamma + \sum_{n=1}^{\infty}\zeta (k+1)(-z)^{k} $ how do you get then that $ \psi (1)= -\gamma $ this is my doubt :D thanks for your answer
Feb
3
comment Minus sign differential operators
the minus sign is to make the operator selfadjoint and so all the eigenvalues are always real and positive as a counter example imagine $ \frac{d^{2}f}{dx}= \lambda_{n}f(x) $ with conditions $ y(0)=y(1)=0$ are the eigenvalues real
Feb
1
comment Weak derivative of one parameter group and the domain of its generator
your limit shoudl it be $ (\phi | i \frac{dA}{dt}|\phi ) $
Jan
31
comment Euler-Maclarurin summation formula and regularization
thanks :) however i would more interested in regularizing divegent integrals $ \int_{0}^{\infty}x^{a}dx $ from zeta regularization $ \zeta (-a) $
Jan
26
comment How can one find this limit
take a calculatro and you will check that tends to 0 :D because of the exponential below :D