What is Transform: Definition and 1000 Discussions

In mathematics, the Laplace transform, named after its inventor Pierre-Simon Laplace (), is an integral transform that converts a function of a real variable



t


{\displaystyle t}
(often time) to a function of a complex variable



s


{\displaystyle s}
(complex frequency). The transform has many applications in science and engineering because it is a tool for solving differential equations. In particular, it transforms linear differential equations into algebraic equations and convolution into multiplication.For suitable functions f, the Laplace transform is the integral






L


{
f
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s
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=



0





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e


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.


{\displaystyle {\mathcal {L}}\{f\}(s)=\int _{0}^{\infty }f(t)e^{-st}\,dt.}

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  1. R

    Does the Fourier Transform Reveal the Magic of Video Segmentation?

    Magic of Fourier Transform? Hello everyone,i am doing my project in image processing... i have done video sementation using the Fourier transform . I applied 3-D fft on video frames ((gray image(2D)+no of video frames(1D)=3D) and Obtained magnitude and phase spectrum and reconstructed video...
  2. K

    Fourier Transform of e^(ip0x)F(x) to F(p)

    Homework Statement f(p) is the Fourier transform of f(x). Show that the Fourier Transform of eipox f(x) is f(p- p0).Homework Equations I'm using these versions of the Fourier transform: f(x)=1/√(2π)∫eixpf(p)dx f(p)=1/√(2π)∫e-ixpf(x)dx The Attempt at a Solution I have...
  3. T

    2D Fourier Transform on a non-rectangular space

    2D Fourier Transform on a non-rectangular area Is it possible to perform a Fourier transform on a shape instead of a rectangular region? To be specific I am attempting to make a linear zoom function that doesn't produce any pixelation and that mimics natural blur that occurs with distance...
  4. M

    What does a fourier transform do?

    hey pf! physically, what does a Fourier transform do? physically what comes out if i put velocity in? thanks! josh
  5. R

    Fourier transform question, keep getting zero, minus infinity limit

    calculate the Fourier transform of the function g(x) if g(x) = 0 for x<0 and g(x) = ##e^{-x}## otherwise. putting g(x) into the transform we have: ##\tilde{g}(p) \propto \int_{0}^{inf} e^{-ipx} e^{-x} dx## which we can write: ##\tilde{g}(p) \propto \int_{0}^{inf} e^{-x(ip+1)} dx##...
  6. K

    Fourrier transform of cos

    Fourier transform of density matrix of cos(x+y)*cos(x-y) I would like to know whether there exists a solution to the following integral, \frac{1}{\pi} \int\limits_{-\infty}^{\infty} \cos(x+y)^\alpha \cos(x-y)^\alpha e^{2ipy} The above expression is the Fourier transform of the...
  7. P

    Non-Convex Coordinate Transform Problem Rotating Frame

    I am sure this is not the best description of the problem, so let me know how I can clarify. Say there are 2 coordinate systems, with one orbiting around the other. Call one fixed ƒ and the other rotating ρ. The goal is to find the transform between the two frames. What's known is 1) A...
  8. J

    Fourier Transform, Discrete Forier Transform image processing

    Hi all, Now naturally after completing a physics degree I am very familiar with the form and function of the Fourier Transform (FT) but never have grasped it quite conceptually. I understand that given a function f(x) I can express every functional value as a linear combination of complex...
  9. A

    Conditions for Laplace and its inverse transform to exist

    I usually see that Laplace transform is used a lot in circuit analysis. I am wondering why can we know for sure that the Laplace and its inverse transform always exists in these cases. Thank you.
  10. J

    MHB Laplace Transform, Finding solution: y′′+4y′+4y=f(t)

    y′′+4y′+4y=f(t) where f(t)=cos(ωt) if 0<t<π and f(t)=0 if t>π? The initial conditions are y(0) = 0 , y'(0) = 1 I know that f(t)=cos(ωt)−uπ(t)cos(ωt), the heaviside equation. AND ω is allowed to vary, supposed to find the general solution, i.e. f(t) in terms of ω I think that after...
  11. J

    Laplace Transform to Find Solution

    Use Laplace transfer to find the solution of the following initial value problem: y''+4y'+4y=f(t) where f(t) = cos(ωt) if 0<t<π and f(t)=0 if t>π ? Also, y(0) = 0, y'(0) = 1 Currently, I have gotten to here, but not sure how to perform inverse Laplace: (s+2)² * F(s) − 1 = [s/(s²+w²)]...
  12. M

    Inverse Laplace Transform and Court

    Homework Statement I had a question in my midterm, it was to find inverse laplace tansform of: (4s+5) / (s^2 + 5s + 18.5) Where ^ denotes power. Homework Equations The Attempt at a Solution My answer was to find the complex roots of equation (s^2 + 5s + 18.5) , by them...
  13. F

    Radon transform, Buffon's needle and Integral geometry

    In all the literature that I have seen it is mentioned that these two are "branches" of integral geometry, but no where I can see the exact connection since one is connected with probability and the other is an integral. I have seen this, but it is not clear...
  14. A

    Fourier transform of function times periodic function

    Suppose I have a function of the type: h(t) = g(t)f(t) where g(t) is a periodic function. Are there any nice properties relating to the Fourier transform of such a product? Edit: If not then what about if g(t) is taken as the complex exponential?
  15. A

    Laplace transform for set of differential equations

    I have a set of differential equations with the basic form: dy_n/dt = t*(a_(n-1)*y_(n-1)+b(n+1)*y_(n+1)-2c_n*y_n) So the time depence is a simple factor in front of the coefficient matrix. Does this set of differential equations have closed form solutions?
  16. J

    Fourier integral and Fourier Transform

    Which is the difference between the Fourier integral and Fourier transform? Or they are the same thing!? Fourier integral:
  17. K

    Laplace Transform solution for 2nd order differential equation

    Homework Statement d^2x/dt^2 - 3 dx/dt + 2x= 2e^3t give that at t=0, x=5, and dx/dt=7 Homework Equations i can't figure out how to derive the values of A, B, and C from the attempted equation solution. please help me out here. thanks The Attempt at a Solution
  18. M

    Solving a Laplace Transform Problem: Where Am I Going Wrong?

    I'm out of college and am brushing up on Laplace Transforms. I have a problem I've solved, but I believe the solution I got is wrong and can't find my error. The problem is 2x''-x'=t*sin(t) x(0)=5,x'(0)=3 My solution... Take the Laplace Transform 2(s^2x-5s-3)-(sx-5)=2s/(s^2+1)^2...
  19. U

    Fourier Transform of wavefunction - momentum space

    Homework Statement Find possible momentum, and their probabilities. Find possible energies, and their probabilities. Homework Equations The Attempt at a Solution First, we need to Fourier transform it into momentum space: \psi_k = \frac{1}{\sqrt{2\pi}} \int \psi_x e^{-ikx} dx =...
  20. M

    Fourier transform convolution proof

    Homework Statement Let FT(f) = Fourier transform of f, (f*g)(x) = convolution of f and g. Given FT(f*g) = FT(f)FT(g), the first part of the convolution theorem, show that FT[fg] = [FT(f)*FT(g)]/2pi. Homework Equations Duality: FT2f(x) = (2pi)f(-x) Convolution: (f*g)(x) =...
  21. J

    Fourier transform matrices

    Homework Statement Let F be the 4x4 matrix whose (i, j)th entry is 5ij in F_13 for i, j = 0,1,2, 3. Compute F(hat) and verify that F(hat)F = I Homework Equations The matrix F(hat) is called the inverse discrete Fourier transform of F. The Attempt at a Solution I found that e = 4...
  22. J

    Fourier transform matrices

    Homework Statement (i) Verify that 5 is a primitive 4th root of unity in F13. (ii) Let F be the 4x4 matrix whose (i, j)th entry is 5ij in F13 for i, j = 0,1,2, 3. Compute F(hat) and verify that F(hat)F= I. Homework Equations The matrix F(hat) is called the inverse discrete Fourier...
  23. J

    What is the Laplace transform of tcos4t using the derivative of a transform?

    Homework Statement Evaluate the Laplace of {tcos4t} using the derivative of a transform Ofcourse i know the shortcut way of doing this, but I need to do it the long way. Homework Equations shortcut way t cos bt = \frac{s^2-b^2}{(s^2+b^2)^2} long way transform of a derivative...
  24. P

    Detailed working out Lorentz contraction from the Lorentz transform

    We have a few posters struggling with this, I thought I'd post a step by step guide, to see if it would help. That seems easier than trying to untangle the confused threads we have. We'll see if it works... Setup and notation: We have a rocket, which has a front and a back. We have a...
  25. M

    MHB Fourier Transform property

    Hey! :o Could you give me a hint how to prove the following property of the Fourier transform, when $F[f(x)]=\widetilde{f}(x)$, where $F[f(x)]$ is the Fourier transform of $f(x)$? $$F[ \widetilde{f}(x) ]= \frac{f(-k)}{2 \pi}$$ We know that: $ \widetilde{f}(k)=\int_{- \infty}^{+ \infty}{...
  26. R

    Use the Fourier transform directly to solve the heat equation

    Homework Statement Use the Fourier transform directly to solve the heat equation with a convection term u_t =ku_{xx} +\mu u_x,\quad −infty<x<\infty,\: u(x,0)=\phi(x), assuming that u is bounded and k > 0. Homework Equations fourier transform inverse Fourier transform convolution thm The...
  27. J

    Rotate Plane: Transform z=b-y to Horizontal Plane

    Homework Statement using a rotation transform, show that the plane z = b - y can be transformed to the horizontal plane \widehat{z} = \frac {b} {\sqrt{b^2 + c^2}} Homework Equations ^ The Attempt at a Solution I just need some help understanding the question, if I could get a...
  28. N

    How to calculate this inverse Fourier Transform?

    Homework Statement Take the inverse Fourier Transform of 5[\delta(f+100)+\delta(f-100)]\bigg(\frac{180+j2\pi f*0.0135}{1680+j2\pi f*0.0135}\bigg)Homework Equations g(t)=\int_{-\infty}^{\infty} G(f)e^{j2\pi ft}dt The Attempt at a Solution g(t)=\int_{-\infty}^{\infty}...
  29. S

    Differential equation with Fourier Transform

    Homework Statement Without solving the differential equation, find the differential equation that solves Fourier transformation of given differential equation for ##a>0##. a) ##y^{'}+axy=0## b) For what ##a## is the solution of part a) an eigenfunction of Fourier Transform Homework Equations...
  30. N

    How to calculate Fourier Transform of e^-a*|t|?

    Homework Statement Calculate (from the definition, no tables allowed) the Fourier Transform of e^{-a*|t|}, where a > 0. Homework Equations Fourier Transform: G(f) = \int_{-\infty}^{\infty} g(t)e^{-j\omega t} dt The Attempt at a Solution I thought I'd break up the problem into the two cases...
  31. M

    How do I prove the Fourier transform of f'(x) is iμF(μ) with given conditions?

    Homework Statement Suppose f(x), -\infty<x<\infty, is continuous and piecewise smooth on every finite interval, and both \int_{-\infty}^\infty |f(x)|dx and \int_{-\infty}^\infty |f'(x)|dx are absolutely convergent. Show the Fourier transform of f'(x) is i\mu F(\mu).Homework Equations...
  32. J

    Problems with Fourier transform

    A necessary condition that a function f(x) can be Fourier transformed is that f(x) is absolutely integrable. However, some function, such as |t|, still can be Fourier transformed and the result is 1/w^2, apart from some coefficients. This can be worked out, as we can add a exponential...
  33. A

    Relationship between Fourier series Coefficients and F Transform

    Homework Statement "Suppose x[n] is a DT (discrete time) periodic signal with fundamental period N. Let us define x_{n}[n] to be x[n] for n ε {0, 1,2, ... , N-1} and zero elsewhere. Denote the Fourier transform of x_{n}[n] with X_{n}[e^jω]. How can one find the Fourier Series coefficients...
  34. M

    Laplace transform intuition

    hello pf! i am wondering if anyone here knows of a geometric, intuitive explanation for the laplace transform? if so, please direct me to the source of if you could, explain to me your understanding? thanks!
  35. D

    Inverse Discrete Time Fourier Transform (DTFT) Question

    1. Given: The DTFT over the interval |ω|≤\pi, X\left ( e^{jω}\right )= cos\left ( \frac{ω}{2}\right ) Find: x(n) 2. Necessary Equations: IDTFT synthesis equation: x(n)=\frac{1}{2\pi}\int\limits_{-\pi}^{\pi}X\left ( e^{jω} \right ) e^{j\omega n}d\omega Euler's Identity...
  36. rogeralms

    Fourier Transform Homework: Determine F(k) & Plot Result

    Homework Statement Determine the Fourier Transform of the function shown. Plot the result using excel, MathCad, or Matlab. See attachment for figure of triangle above x-axis from -X0/2 tp X0/2 with a max height of 1 at x=0. Homework Equations The answer is F(k) = X0/2 [sin(kX0/4) /...
  37. H

    What is the Fourier transform of this function ?

    Hi, I have problems finding out the Fourier transform of the following function, 1/\sqrt{q^2 + m^2}, where m\neq 0 denotes a parameter. It seems easy, but I don't know how. Could anybody show me how to do it ? Thanks in advance. hiyok
  38. L

    Inverse fourier transform of constant

    Homework Statement Find the inverse Fourier transform of f(w)=1 Hint: Denote by f(x) the inverse Fourier transform of 1 and consider convolution of f with an arbitrary function. Homework Equations From my textbook the inverse Fourier transform of f(w)=\int F(w)e^-iwt dw The...
  39. R

    MHB Transform Random Var CDF to Standard Normal: F(x)=1-exp(-sqrt x)

    How to transform a random variable CDF to a standard normal Given F(x) = 1- exp (-sqrt x), for x greater that 0 Thanks.
  40. P

    Fast Fourier Transform (FFT) power spectrum angle

    Dear Physics Buddies, How are well all, okay I hope. I was wondering if I might browse all your infinite intellects and ask you a very simple question. I am working with some medical images in MATLAB and my collaborators would like to know the orientation of the fibres that it contains...
  41. P

    MHB Douglas' question via email about Inverse Laplace Transform

    To start with, let's work on the Partial Fraction decomposition. $\displaystyle \begin{align*} \frac{A\,s + B}{s^2 - 16s +128} + \frac{C\,s + D}{s^2 + 16s + 128} &\equiv \frac{3s}{s^4 + 16\,384} \\ \frac{ \left( A\,s + B \right) \left( s^2 + 16s + 128 \right) + \left( C\,s + D \right) \left(...
  42. Choisai

    Focused diffraction and Fourier transform

    After searching on the web and reading a bit, I found that lenses can perform Fourier transform. All you need to do is put a transparant object in front of it, like a transparant sheet with black stripes on it and a screen behind the lens(so basically a 4f setup). The lens will then perform a...
  43. B

    Fourier transform vs Inner product

    So the complex exponential Fourier series form an orthonormal basis for the space of functions. A periodic function can be represented with countably many elements from the basis, and an aperiodic function requires uncountably many elements. Given a signal, we can find the coefficients of the...
  44. D

    MHB Solving Laplace Transform: \[(s+1)^2/(s^2-s+1)\]

    \[ \frac{(s+1)^2}{s^2 - s + 1} \] I have simplified it down to \[ \frac{s - \frac{1}{2} + s^2 + s + \frac{3}{2}}{(s - 1/2)^2 + \frac{3}{4}} = e^{1/2t}\cos\Big(t\frac{\sqrt{3}}{2}\Big) + \sqrt{3}e^{1/2t}\sin\Big(t\frac{\sqrt{3}}{2}\Big) + \frac{s^2 + s}{(s - 1/2)^2 + \frac{3}{4}} \] but I can't...
  45. D

    MHB Magnitude Fourier transform lowpass, highpass, or bandpass

    Using geometric evaluation of the magnitude of the Fourier transform from the corresponding pole-zero plot, determine, for each of the following Laplace transforms, whether the magnitude of the corresponding Fourier transform is approximately lowpass, highpass, or bandpass. \[ H_1(s) =...
  46. D

    MHB Inverse Laplace transform question

    With a Laplace transform, we can remember common set ups; for example, \[ \mathcal{L}\{e^{-at}\} = \frac{1}{s + a}. \] When it comes to the inverse Laplace transform, I can only find the tables to remember in a book. However, if we go back to the Laplace transform, we can always do \[...
  47. J

    An analytic solution for a fourier transform

    Homework Statement the function is Exp[-w^2]/w^2, how to solve the Fourier transform analytically with Residue theorem? It is better if there is more general results. Mathematica can solve it analytically, but I need a human-soluable way. Homework Equations The Attempt at a...
  48. L

    Fourier transform. Impulse representation.

    ##\varphi(p)=\frac{1}{\sqrt{2\pi\hbar}}\int^{\infty}_{-\infty}dx\psi(x)e^{-\frac{ipx}{\hbar}}##. This ##\hbar## looks strange here for me. Does it holds identity ##\int^{\infty}_{-\infty}|\varphi(p)|^2dp=\int^{\infty}_{-\infty}|\psi(x)|^2dx=1##? I'm don't think so because this ##\hbar##. So...
  49. I

    How does magnetic moment transform due to relativity?

    Hi, I have seen textbooks model how an electric field of an electron changes when viewed from another frame of reference. In these models, the electric fields seems to "compress" along the axis of motion. What happens to the magnetic moment in these situations? Does the magnetic moment also get...
  50. D

    4 Lens optical system/fourier transform

    Question on my study guide: An optical systems consists of 4 lenses spaced apart. Each lens has a focal length f. Each lens is located a distance "z" away from each plane as shown. The total length of the system is 8z. Find the distance z needed to satisfy a FOURIER TRANSFORM condition...
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