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1620
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location Spain , Basque Country , Bilbao
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visits member for 3 years, 3 months
seen Jan 2 at 11:03

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 :)


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
Jan
26
comment Evaluating $\lim\limits_{x\rightarrow \infty} \frac{f(x)}{x}$ knowing $\lim\limits_{x\to\infty} f(x+1) - f(x)$
for big 'x' $ f(x+1)-f(x) \sim f'(x)$
Jan
23
comment Limit of $\frac{1}{x}\ln{\frac{\exp{x}-1}{x}}$
i have used my calculator and obtained $ 0.49.. $ with $ x=0.0001 $ so the limit must be $ 0.5 $ :D
Jan
21
comment what is the period of this sinusoidal function funtion
we know that $ cos(u+2\pi ) = cos (u) $ for every 'u' so set $ u= \frac{4n \pi}{31}+ \frac{\pi}{5} $
Jan
18
comment evaluation of integral
for big 'x' the integral looks like $ \frac{e^{-2x}}{x} $ so only numerical methods work for this integral , see mathworld.wolfram.com/ExponentialIntegral.html
Jan
17
comment possible value of this series ? either convergent or in the borel sense?
ok thanks :D i didn't know how i cuold not get this solution by myself..
Jan
15
comment “All math is useful eventually”
we can't prove your affirmation even there is physics which eventally will worth nothing is a pity :( for example i can not ge t a job because my math is unesefull :D vixra.org/author/jose_javier_garcia_moreta
Jan
12
comment Why are mathematical proofs that rely on computers controversial?
i think computers does not understand INFINITY am i wrong ? , also unfortunately a numerical proof is not valid otherwise i would have found an operator which yields to Riemann zeros :D :D
Oct
31
comment Laplace, Legendre, Fourier, Hankel, Mellin, Hilbert, Borel, Z…: unified treatment of transforms?
in many cases an integral transform $ g(s)=s\int_{0}^{\infty}K(st)f(t) $ can be solved by using the Borel transform, not only for the case $ K(st)=e^{-st} $
Oct
26
comment Given a plot of a function $f(x)$ how to find at which points it is differentiable?
i think you can not.. assume a discontinuity poitn at ceratin value 'a' so for any positive $ \epsilon $ we hve $ f(x+ \epsilon)= 10^{-30000000000000000000000000000000000000000000000000000000000000}+f(x-\epsilo‌​n) $
Oct
15
comment Result of $\sum_{n=1}^{\infty} \frac{\sin(nx)}{n}$
en.wikipedia.org/wiki/Floor_and_ceiling_functions therefore the sum is about $ \frac{\pi}{2}- frac{x}{2\pi} $
Oct
11
comment Laurent series expansion of a function defined by an integral
well perhaps this exists at some other point $ y=1$ or soemthing :)
Oct
11
comment Evaluate $\lfloor \frac{x}{m} \rfloor + \lfloor \frac{x+1}{m} \rfloor + \dots + \lfloor \frac{x+m-1}{m} \rfloor $
this fucntion is periodic $ f(x)=f(x+m) $ so you could try a Fourier series representation for it