Function Definition and 1000 Threads

  1. abdulbadii

    Failed function within SMPS giving weak current

    What is the very common culprit component and what is its function within SMPS having weak current, far weaker than its rating while its voltage is always perfect?
  2. loversphisics

    I Proving Behavior of Particle in Infinite Potential: Wave Function?

    Hello, guys! I have a question. How can I prove the behavior of a particle subjected to an infinite potential? Will the wave function exist?
  3. M

    Deriving Wave Function for One-Dimensional Sinusoidal Wave

    Where did they get the equation in circled in red from? It does not seem that it can be derived from the graph below. Many thanks
  4. M

    Engineering How to implement a transfer function in Simulink with variable coefficients?

    The implementations for the two filters in simulink are as follow: For the first filter: For the second one: The obtained results have values of 10^-12, while the expected results should be between 10^-3 - 10. Since it's the first time when I try t implement a tf with variable coefficients I...
  5. yucheng

    I Fermi's golden rule: why delta function instead of density states?

    Sakurai, in ##\S## 5.7.3 Constant Perturbation mentions that the transition rate can be written in both ways: $$w_{i \to [n]} = \frac{2 \pi}{\hbar} |V_{ni}|^2 \rho(E_n)$$ and $$w_{i \to n} = \frac{2 \pi}{\hbar} |V_{ni}|^2 \delta(E_n - E_i)$$ where it must be understood that this expression is...
  6. I

    I QED/Quantum Mechanics: Probability or Spatial Function?

    In "QED, The Strange Theory of Light And Matter" Richard Feynman describes the probability path of a single photon emitted from a source, reflected from a mirror surface, and finally reflected to a probe detector. This path is the least time path relative to the probe/viewer, determined by the...
  7. L

    I Create a surjective function from [0,1]^n→S^n

    the first method is this : I think I can create a surjective function f:[0,1]^n→S^n in this way : [0,1]^n is omeomorphic to D^n and D^n/S^1 is omeomorphic to S^n so finding a surjective map f is equal to finding a surjective map f':D^n →D^n/S^n and that is quotient map. Now if I take now a...
  8. C

    Formula for Xo and Yo for graph of quadratic function

    Can someone please tell me where I am wrong. I am learning how to write ##a^{2} + bx + c## in this form ##f(x)= a(X-X_0)^{2} +Y_0##. The method used in my textbook is a reduction to the perfect square. And it goes like this: ##f(x)=ax^2+bx+c## ##=a[x^2+\frac{b}{a}x]+c## ##=a\left [...
  9. R

    I Multivariable function optimization inconsistency

    Mentor note: For LaTeX here at this site, don't use single $ characters -- they don't work at all. See our LaTeX tutorial from the link at the lower left corner of the input text pane. I have a function dependent on 4 variables ##f(r_1,r_2,q_1,q)##. I'm looking to minimize this function in the...
  10. V

    Is it possible to find the range of this function?

    I can get the domain, but getting the range seems impossible. Domain $$x-5=0$$ $$x =5$$ $$\therefore x \in (- \infty ,5) \cup (5, + \infty)$$ Range  I can simplify the function to the form below, but I don't know how to go from there. $$ f(x)= x + 5 + \frac {1}{x-5}$$  
  11. P

    A Norm 2, f Integrable function, show: ##||f-g||_2<\epsilon##

    Let ##F:[0,2\pi] --> Complex## ##F## is integrable riemman. show for all ##\epsilon>0## you can find a ##g##, continuous and periodic ##2\pi## s,t: ##||f-g||_2<\epsilon## What I tried ( in short ), which is nothing almost, but all I know: because g in continuous and periodic, according to...
  12. hagopbul

    An idea to improve kidney function

    Hello All : as i read about solid state physics , reading about crystals and structures , is it possible to create PZE electrodes and put them on kidney to create some vibrations patterns to help in filtration of blood reducing the need to kidney dialyses , as kidney problem is filtration...
  13. C

    The derivative of uv wrt x using st function (homework problem)

    TL;DR Summary: I attempt to find the derivative of uv with respect to x using non standard analysis, hyperreals, and the standard part function st; I take u to be a function of x, and I also take v to be a function of x. Hello everyone! I've been learning about non standard analysis concepts...
  14. P

    A Vector calculus - Prove a function is not differentiable at (0,0)

    ##f\left(x\right)=\begin{cases}\sqrt{\left|xy\right|}sin\left(\frac{1}{xy}\right)&xy\ne 0\\ 0&xy=0\end{cases}## I showed it partial derivatives exist at ##(0,0)##, also it is continuous as ##(0,0)## but now I have to show if it differentiable or not at ##(0,0)##. According to answers it is not...
  15. H

    B Can we all agree "consciousness" is not required to collapse wave function?

    I see this written or talked about so often. Pop-sci for sure. But, whatever the wave function is, and whatever might collapse it, can we agree consciousness is not required to collapse it? I.E., the moon was there before "conscious" beings, on this planet or elsewhere, viewed it? Is at...
  16. H

    B Why does anyone think gravity might collapse wave function?

    Why on Earth does anyone, let along Roger Penrose, think gravity might be what causes the wave function to collapse? The most basic experiment in quantum physics, the double slit experiment, shows that collapse is most closely analogous to whether or not the item at issue (for example, an...
  17. PhysicsRock

    How to Show Linearity of a Function?

    I don't really know how I am supposed to approach that. In general, I know how to show that a function is linear, which is to show that ##f(\alpha \cdot x) = \alpha \cdot f(x)## and ##f(x_1 + x_2) = f(x_1) + f(x_2)##. However, for this specific function, I have no idea, since there is nothing...
  18. mcastillo356

    Why does this function make it easy to prove continuity with sequences?

    I've been given the proof, but don't understand; to calculate the limit of ##f## when ##x## tends to zero it's enough to see that if ##\{x_n\}_{n=1}^\infty## is a sequence that tends to ##0##, then...
  19. M

    Deriving position function for object in SHM

    For this problem, How did they get that formula shown? My working is, All the solutions wrote was, Many thanks!
  20. P

    I Can an inverse function of a special cubic function be found?

    Like this one: ##f(x)=3x^3 -18x^2 +36x##.Is there any way to find the inverse of this function without using the general solution to cubic equation?
  21. G

    Apply the Legendre Transformation to the Entropy S as a function of E

    Hi, Unfortunately I am not getting anywhere with task three, I don't know exactly what to show Shall I now show that from ##S(T,V,N)## using Legendre I then get ##S(E,V,N)## and thus obtain the Sackur-Tetrode equation?
  22. V

    Matlab Function for Composite Simpson

    function I=main_simpson(a,b,tol) f = @(x) sin(1./x); SO = 0; N = 10; S = 1; while (abs(S-SO)>tol) SO = S; h = (b-a)/(2*N); i = 0:N-1; xi = a+2*i*h; xi1 = a+2*(i+0.5)*h; xi2 = a+2*(i+1)*h; S = (h/3)*sum(f(xi)+4*f(xi1)+f(xi2)); N = 2*N; end end <Moderator's note...
  23. Expiring

    I Showing That a Function Does Not Have Two Distinct Roots

    I am wondering if someone can look over my proof, and point out any mistakes I might have made.There is no value of m such that x^3 - 3x + m = 0 has two distinct roots on the interval 0 <= x <= 1. Proof. Let f(x) = x^3 - 3x + m. Suppose, to the contrary, that there is a value of m such that f...
  24. jaumzaum

    B Can a function have two fundamental periods?

    I was wondering if a periodic function could have 2 different fundamental periods? If so, could you give an example? And If not, how can I prove that?
  25. chwala

    Prove the hyperbolic function corresponding to the given trigonometric function

    ##8 \sin^4u = 3-4\cos 2u+\cos 4u## ##8 \sinh^4u = 3-4(1+2\sinh^2 u)+ \cosh ( 2u+2u)## ##8 \sin^4u = 3-4-8\sinh^2 u+ \cosh 2u \cosh 2u + \sinh 2u \sinh 2u## ##8 \sinh^4u = 3-4+1-8\sinh^2 u+ 4\sinh^2u +4\sinh^4 u + 4\sinh^2 u + 4\sinh^4 u## ##8 \sinh^4u = -8\sinh^2 u+ 8\sinh^2u +8\sinh^4 u##...
  26. K

    Normalize function - quantum chemistry

    Normalize function f(r) = Nexp{-alpha*r} Where alpha is positive const and r is a vector I was just wondering if the fact that we have a vector value in our equation changes anything about the solution
  27. T

    I Hubble Parameter as function of time in universe models

    This graph shows ##H## as a function of time related to the L-CDM model. Do we (@Jorrie) have similar graphs e.g. for ##\Lambda=0##; ##k=-1## critical, ##\Lambda=0##; ##k=0## open, ##\Lambda=0##; ##k=+1## closed? That would be great, thanks in advance.
  28. H

    What Is the Correct Partition Function for a Spin System?

    ##Z = \sum_{-i}^{i} = e^{-E_n \beta}## ##Z = \sum_{0}^j e^{nh\beta} + \sum_{0}^j e^{-nh\beta}## Those sums are 2 finites geometric series ##Z = \frac{1- e^{h\beta(i+1)}}{1-e^{h\beta}} + \frac{1-e^{-h\beta(i+1)}}{1-e^{-h\beta}}## I don't think this is ring since from that I can't get 2 sinh...
  29. Jimyoung

    Why is the Entropy of the Universe (total entropy) a path function?

    I understand that S (Ssys) is a state function but I can't understand why Ssurr and Suniv (or Stot) are a path function.
  30. S

    Comp Sci Plot periodic function with Fourier coefficients

    I have plotted the function for ##T=15## and ##\tau=T/30## below with the following code in Python: import numpy as np import matplotlib.pyplot as plt def p(t,T,tau): n=np.floor(t/T) t=t-n*T if t<(2*np.pi*tau): p=np.sin(t/tau) else: p=0 return p...
  31. J

    B Solving Kepler's 1st law as a function of time

    Hi I posted this differential equation to WolframAlpha https://www.wolframalpha.com/input?i2d=true&i=Power[\(40)Divide[a,1+b*cos\(40)y\(40)x\(41)\(41)]\(41),2]*y'\(40)x\(41)=c but no solution , " Standard computation time exceeded... Try again with Pro computation time " Should I ( buy and )...
  32. Q

    Integration of structure function F2 to calculate quark momentum

    I study particle physics with “Particles and Nuclei” / Povh et al. and “Modern particle physics” / Mark Thomson and I am currently at “Deep-Inelastic scattering”. After introducing several scattering equations, such as Rosenbluth, that all include terms for electric AND magnetic scattering, i.e...
  33. P

    Introduce an integral function in a spreadsheet (Excel MS)

    I found some interesting equations on cosmology and I was wondering how to introduce the integral in an excel sheet: "Paste ( .443s^3+1)^(-1/2) in for the integrand, type in s for the variable and 1 to 2 for the limits. Press submit, then change 2→3→4→5 and repeat." (from the thread...
  34. chwala

    Solve this problem that involves a probability density function

    I am refreshing on this; ..after a long time... Note that i do not have the solution to this problem. I will start with part (a). ##f(u)= 3u-\dfrac{3u^2}{2k}## with limits ##0≤u≤k## it follows that, ##3k - \dfrac{3k}{2}=1## ##\dfrac{3k}{2}=1## ##k=\dfrac {2}{3}## For part (b)...
  35. K

    A How to check if a function doesn't depend on a variable?

    Hello! I have some experimental data points ##(z_i,dz_i)## and I know that in the most general case this variable can be written in terms of 2 other variables as ##z_i = ay_i+bx_i##. Beside ##z_i## I can also measure, for each point, ##x_i## (we can assume that the uncertainty in ##x_i## is...
  36. T

    I Closed Form for Complex Gamma Function

    Hey all, I was wondering if there was an equivalent closed form expression for ##\Gamma(\frac{1}{2}+ib)## where ##b## is a real number. I came across the following answer...
  37. G

    I How Is the Partition Function of BaTiO3 Calculated in a Cubic Lattice?

    I have a cubic lattice, and I am trying to find the partition function and the expected value of the dipole moment. I represent the dipole moment as a unit vector pointing to one the 8 corners of the system. I know nothing about the average dipole moment , but I do know that the mean-field...
  38. PhysicsRock

    I Is the solution to this problem as trivial as I think?

    The problem goes as follows: Let ##M, N## be sets and ##f : M \rightarrow N##. Further let ##L \subseteq M## and ##P \subseteq N##. Then show that ##L \subseteq f^{-1}(f(L))## and ##f^{-1}(f(P)) \subseteq P##. Obviously, I would simply use the definition of a functions inverse to obtain...
  39. H

    Kramers-Kronig, parity and delta function

    Hi, First of all, I'm not sure to understand what he Kramers-kronig do exactly. It is used to get the Real part of a function using the imaginary part? Then, when asked to add a peak to the parity at ##\omega = -\omega_0##, is ##Im[\epsilon_r(\omega)] = \delta(\omega^2 - \omega_0 ^2)## correct...
  40. Barbequeman

    Did I Calculate the Salpeter Initial Mass Function Correctly?

    I calculated the following in the attached file, I hope I did it correctly...
  41. H

    Monotonic sequence definition of Continuity of a function

    Question: There is a function ##f##, it is given that for every monotonic sequence ##(x_n) \to x_0##, where ##x_n, x_0 \in dom(f)##, implies ##f(x_n) \to f(x_0)##. Prove that ##f## is continuous at ##x_0## Proof: Assume that ##f## is discontinuous at ##x_0##. That means for any sequence...
  42. S

    Antiderivative of Heaviside step function with absolute-value-argument

    For ##R<0##, the antiderivative is just a constant, since then ##R-|x|## is negative for all values of ##x##, which in turn implies ##\Theta(R-|x|)## is zero for all values of ##x##. For ##R\geq 0##, and by inspection apparently, the antiderivative is ##(R+x)\Theta(R-|x|)+2R\Theta(x-R)+C.##...
  43. LCSphysicist

    Partition function of modified Ising model

    $$H = - J ( \sum_{i = odd}) \sigma_i \sigma_{i+1} - \mu H ( \sum_{i} \sigma_i ) $$ So basically, my idea was to separate the particles in this way:: ##N_{\uparrow}## is the number of up spin particles ##N_{\downarrow}## "" down spin particles ##N_1## is the number of pairs of particles close...
  44. N

    I Finding Max and Min Extremes of a Function with Second Derivatives Equal to Zero

    What should I do when the f(x, y) function's second derivatives or Δ=AC-B² is zero? When the function is f(x) then we can differentiate it until it won't be a zero, but if z = some x and y then can I just continue this process to find what max and min (extremes) it has? What I've done is...
  45. chwala

    Express a function as a sum of even and odd functions

    I am refreshing on this; of course i may need your insight where necessary...I intend to attempt the highlighted...this is a relatively new area to me... For part (a), We shall let ##f(x)=\dfrac{1}{x(2-x)}##, let ##g(x)## be the even function and ##h(x)## be the odd function. It follows...
  46. N

    I Why can't we just integrate a simple function?

    Can anyone explain to me why the second one is the right? (See the attachment)
  47. PhysicsRock

    Exploring an Unexplored Expression for the Beta Function

    So, I've recently played around a little with the Gamma Function and eventually managed to find an expression for the Beta Function I have not yet seen. So I'm asking you guys, if you've ever seen this expression somewhere or if this is a new thing. Would be cool if it was, so here's the...
  48. Euge

    POTW Contour Integral Representation of a Function

    Suppose ##f## is holomorphic in an open neighborhood of the closed unit disk ##\overline{\mathbb{D}} = \{z\in \mathbb{C}\mid |z| \le 1\}##. Derive the integral representation $$f(z) = \frac{1}{2\pi i}\oint_{|w| = 1} \frac{\operatorname{Re}(f(w))}{w}\,\frac{w + z}{w - z}\, dw +...
  49. chwala

    I Understanding Removable discontinuity of the given function: ##e^x##

    I would like to understand the highlighted part. In my understanding, this function does not seem to have a hole! Having said this, i can state that ##x_0=1## and we have our defined ##f(x_0)=2##. It follows that, ##f(1^{+}) = e## ##f(1^{-}) = e## thus ##f(x_0^{+})=f(x_0^{-})≠f(x_0)## thus the...
  50. Franklie001

    Engineering RLC circuit -- Phasor Transfer Function calculation

    Good morning, I need some help solving those two question. I've attached my attempted solution below. Could i solve the transfer function any further? Thank you for your help
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