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
}
(
s
)
=



0





f
(
t
)

e


s
t



d
t
.


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

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  1. U

    Help with evaluating this Fourier transform

    The definition of Fourier transform (F.T.) that I am using is given as: $$f(\vec{x},t)=\frac{1}{\sqrt{2\pi}}\int e^{-i\omega t}\tilde{f}(\vec{x},\omega)\,\mathrm{d}\omega$$ I want to show that: $$\frac{1}{c\sqrt{2\pi}}\int e^{-i\omega t}\omega^2...
  2. willDavidson

    Laplace Transform Finding Open-Circuit Voltage

    I am interested in modeling a battery charging/discharging. I am starting off with a simple model using a voltage source in series with a parallel RC branch which is in series with a resistor. I will be measuring the open circuit voltage between the last series resistor and the bottom of the...
  3. redtree

    I Fourier transform of a vector

    Given ##f(\vec{x})##, where the Fourier transform ##\mathcal{F}(f(\vec{x}))= \hat{f}(\vec{k})##. Given ##\vec{x}=[x_1,x_2,x_3]## and ##\vec{k}=[k_1,k_2,k_3]##, is the following true? \begin{equation} \begin{split} \mathcal{F}(f(x_1))&= \hat{f}(k_1) \\ \mathcal{F}(f(x_2))&= \hat{f}(k_2) \\...
  4. N

    I Get the time axis right in an inverse Fast Fourier Transform

    Hi I would like to transform the S-parameter responce, collected from a Vector Network Analyzer (VNA), in time domain by using the Inverse Fast Fourier Transform (IFFT) . I use MATLAB IFFT function to do this and the response looks correct, the problem is that I do not manage to the time scaling...
  5. S

    Fourier transform of electric susceptibility example

    I have not studied the Fourier transform (FT) in great detail, but came across a problem in electrodynamics in which I assume it is needed. The problem goes as follows: Evaluate ##\chi (t)## for the model function...
  6. E

    B Transform to accelerating coordinates

    It's a silly example, but hopefully it will help me to understand the maths. Two guys ##A## and ##B## are initially at the same spacetime event ##O##, and then ##B## receives an impulse along the ##x##-direction giving him an initial coordinate velocity ##\dot{x}_B = v_0## as measured by ##A##...
  7. PhysicsTest

    Clarke Transform Clarification

    The standard Clarke Transform is ## i_{alpha} = i_a; -> 1 i_{beta} = \frac {(i_a + 2i_b)} {\sqrt3} ->2 ## I am trying to derive it, but missing a factor. Basically converting the 3 phase currents ## I_a, I_b, I_c ## into the 2 axis ##I_{\alpha}, I_{\beta} ## resolving along the x-axis...
  8. .Scott

    The Fast Fourier Transform is described in the Quantum Domain

    In August, "Quantum Information Processing" published an article describing a full FFT in the quantum domain - a so-called QFFT, not to be confused with the simpler QFT. According to the publication:
  9. rannasquaer

    MHB How to Solve Laplace Transforms with a Fractional Term?

    How to solve the transforms below \[ \mathscr{L}^{-1} \frac{a(s+2 \lambda)+b}{(s+ \lambda)^2- \omega^2} \]
  10. S

    Mathematica Fourier Transform Help with Mathematica

    I am attempting to be able to do this problem with the help of Mathematica and Fourier transform. My professor gave us instructions for Fourier Transformation and Inverse Fourier, but I don't believe that my output in Mathematica is correct.
  11. S

    I Why should a Fourier transform not be a change of basis?

    I was content with the understanding of the Fourier transform (FT) as a change of basis, from the time to the frequency basis or vice versa, an approach that I have often seen reflected in texts. It makes sense, since it is the usual trick so often done in Physics: you have a problem that is...
  12. Frankenstein19

    I Laplace transform linearity problem

    I've included the problem statement and a bit about the function but my main issue is with the equation after "then" and the one with the red asterisk. I don't understand why the Laplace transform for a u(t)*e^(-t/4) isn't (1/s)*(1/(s+1/4)). The book I am reading says it's(1/(s+1/4)).
  13. B

    Question about the Lorentz transform

    Image below. Is the Lorentz transform just switching between a stationary frame and a moving frame? I forgot to write Alice's frame but I assume that is obvious.
  14. M

    Engineering Fourier Transform: best window to represent function

    Hi, I was hoping to gain more insight into these window questions when looking at frequency spectra questions. I don't really know what makes windows better than one another. My attempt: In the question, we have f(t) = cos(\omega_0 t) and therefore its F.T is F(\omega ) = \pi \left(...
  15. thaiqi

    Fourier transform of Maxwell's equations

    Hello, I am unfamiliar with Maxwell's equations' Fourier transform. Are there any materials talking about it?
  16. B

    Why is the heaviside function in the inverse Laplace transform of 1?

    Homework Statement:: Why is the heaviside function in the inverse laplace transform of 1? Relevant Equations:: N/A This is a small segment of a larger problem I've been working on, and in my book it gives the transform of 1 as 1/s and vice versa. But as I've looked online for help in figuring...
  17. thaiqi

    I Lorentz Transform Deduction: Question Explained

    I read in one book about the deduction of Lorentz transform. It writes: ' $$ \begin{aligned} t^\prime & = \xi t + \zeta x (1) \\ x^\prime & = \gamma x + \delta t (2) \\ y^\prime & = y (3) \\ z^\prime & = z (4) \end{aligned} $$ from (2), it gives: $$ \begin{aligned} {dx \over dt} = -{ \delta...
  18. agnimusayoti

    What is the Exponential Fourier Transform of an Even Function?

    From the sketch, I know that this function is an even function. So, I simplify the Fourier transform in the limit of the integration (but still in exponential form). Then, I try to find the exponential FOurier transform. Here what I get: $$g(a)=\frac{2}{2\pi} \int_{0}^{\infty} e^{-x} e^{-iax}...
  19. S

    Laplace transform of an ODE with a non-smooth forcing function

    Suppose I'm solving $$y''(t) = x''(t)$$ where $$x(t)$$ is the ramp function. Then, by taking the Laplace transform of both sides, I need to know $x'(0)$ which is discontinuous. What is the appropriate technique to use here?
  20. A

    A How to transform a probability density function?

    I have the following probability density function (in Maple notation): f (x) = (1 / ((3/2) * Pi)) * (sin (x)) ** 2 with support [0; 3 * Pi] Now I want to transform x so that 0 -> (3/2) * Pi and 3 * Pi -> (15/2) * Pi and the new function is still a probability density function. How should I...
  21. M

    Can I Use a Transformation Matrix to Solve the Radon Transform of a Square?

    Can I attempt this problem using the transformation matrix? I'm not sure how to go about solving this?
  22. M

    Fourier series and the shifting property of Fourier transform

    Summary:: If ##f(x)=-f(x+L/2)##, where L is the period of the periodic function ##f(x)##, then the coefficient of the even term of its Fourier series is zero. Hint: we can use the shifting property of the Fourier transform. So here's my attempt to this problem so far...
  23. Electrical Engi321

    Finding Fourier Transforms of Non-Rectangular Pulses

    Hi, In class I have learned how to find the Fourier transform of rectangular pulses. However, how do I solve a problem when I should sketch the Fourier transform of a pulse that isn't exactly rectangular. For instance "Sketch the Fourier transform of the following 2 pulses" Thanks in advance...
  24. redtree

    I The domain of the Fourier transform

    Given the domain of the integral for the Fourier transform is over the real numbers, how does the Fourier transform transform functions whose independent variable is complex? For example, given \begin{equation} \begin{split} \hat{f}(k_{\mathbb{C}}) &= \int_{\mathbb{R}} f(z_{\mathbb{C}})...
  25. person_random_normal

    I Visualizing the Fourier transform using the center of mass concept

    I found this video on youtube which is trying to explain Fourier transform using the center of mass concept At 15:20 the expression of the x coordinate is given in the video. I believe it is wrong, and it should be: ##\frac{{\int g(t)e^{(-2 \pi ift)}.g(t).2 \pi f.dt}} { \int g(t).2 \pi...
  26. jisbon

    Engineering Nodal Analysis of this Circuit using the Laplace Transform

    Was just practicing some problems on the Fundamentals of Electric Circuits, and came across this question. I understand I will have to transform to the s domain circuit, which looks something like this: Then doing nodal analysis, I will get the following for the first segement (10/s-V1)/1 =...
  27. thereddy

    Discrete Fourier transform question

    Summary:: Discrete Fourier transform exam question Hi there, I'm not really sure how to do this question at all. Any help would be appreciated.
  28. tworitdash

    A Spatial Fourier Transform: Bessel x Sinusoidal

    I(k_x, k_y) = \int_{0}^{R} \int_{0}^{2\pi} J_{m-1}(\alpha \rho) \sin((m + 1) \phi) e^{j\rho(k_x \cos\phi + k_y \sin\phi)} \rho d\rho d\phi Is there any way to do it? J is the Bessel function of the first kind. I thought of partially doing only the phi integral as \int_{0}^{2\pi} \sin((m + 1)...
  29. R

    I Inverse Laplace transform of a rational function

    I struggle to find an appropriate inverse Laplace transform of the following $$F(p)= 2^n a^n \frac{p^{n-1}}{(p+a)^{2n}}, \quad a>0.$$ WolframAlpha gives as an answer $$f(t)= 2^n a^n t^n \frac{_1F_1 (2n;n+1;-at)}{\Gamma(n+1)}, \quad (_1F_1 - \text{confluent hypergeometric function})$$ which...
  30. PainterGuy

    I Magnitude and phase of the Fourier transform

    Hi, A rectangular pulse having unit height and lasts from -T/2 to T/2. "T" is pulse width. Let's assume T=2π. The following is Fourier transform of the above mentioned pulse. F(ω)=2sin{(ωT)/2}/ω ; since T=2π ; therefore F(ω)=2sin(ωπ)/ω Magnitude of F(ω)=|F(ω)|=√[{2sin(ωπ)/ω}^2]=|2sin(ωπ)/ω|...
  31. PainterGuy

    I Fourier transform of rectangular pulses

    Hi, I was trying to find Fourier transform of two rectangular pulses as shown below. The inverted rectangular pulse has unit height, -1, and lasts from -π to 0. The other rectangular pulse has unit height, 1, and lasts from 0 to π. I was making use of Laplace transform and its time shifting...
  32. PainterGuy

    Solving an ODE with the Laplace transform

    Hi again, The previous problem was done using y′′(t)+2y′(t)+10y(t)=10 with with intial condition y(0⁻)=0. In the following case, I'm using an initial condition and setting the right hand side equal to zero. Find y(t) for the following differential equation with intial condition y(0⁻)=4...
  33. PainterGuy

    MATLAB Finding an inverse Fourier transform using the Laplace transform

    Hi, This thread is an extension of this discussion where @DrClaude helped me. I thought that it'd be better to separate this question. I couldn't find any other way to post my work other than as images so if any of the embedded images are not clear, just click on them. It'd make them clearer...
  34. PainterGuy

    I Laplace transform of an expression using transform tables

    Hi, I 'm trying to find the Laplace transform of the following expression. I used the following conversion formulas. I think "1" is equivalent to unit step function who Laplace transform is 1/s. I ended up with the following final Laplace transform. Is my final result correct? Thank you...
  35. L

    Engineering Laplace transform of the given circuit

    Hello i have an assignment. From given circuit i need to find s domain and inverse them back to t domain. can you help me by explain this circuit?
  36. engnrshyckh

    B Inverse Laplace transform

    I used partial fraction method first as: 1/s(s^2+w^2)=A/s+Bs+C/(s^2+w^2) I found A=1/w^2 B=-1 C=0 1/s(s^2+w^2)=1/sw^2- s/s^2 +w^2 Taking invers laplace i get 1/w2 - coswt But the ans is not correct kindly help.
  37. P

    MHB Solving Integral Equation w/ Laplace Transform - Abdullah

    We would need to recognise that the integral in the equation is a convolution integral, which has Laplace Transform: $\displaystyle \mathcal{L}\,\left\{ \int_0^t{ f\left( u \right) \,g\left( t - u \right) \,\mathrm{d}u } \right\} = F\left( s \right) \,G\left( s \right) $. In this case...
  38. P

    MHB Seth's question via email about a Laplace Transform

    Since this is of the form $\displaystyle \frac{f\left( t \right)}{t} $ we should use $\displaystyle \mathcal{L}\,\left\{ \frac{f\left( t \right) }{t} \right\} = \int_s^{\infty}{F\left( u \right) \,\mathrm{d}u } $. Here $\displaystyle f\left( t \right) = \cosh{\left( 4\,t \right) } - 1 $ and so...
  39. B

    Question about the Galilean transform in classical physics

    Shouldn't the equation be x' = x + (v')(t) instead of x' = x + (v)(t)?
  40. P

    MHB Jun's question via email about Laplace Transform

    Upon taking the Laplace Transform of the equation we have $\displaystyle \begin{align*} s^2\,Y\left( s \right) - s\,y\left( 0 \right) - y'\left( 0 \right) + 4\,Y\left( s \right) &= -\frac{8\,\mathrm{e}^{-6\,s}}{s} \\ s^2 \,Y\left( s \right) - 2\,s - 0 + 4\,Y\left( s \right) &=...
  41. Luke Tan

    I Peak of Analytical Fourier Transform

    In a numerical Fourier transform, we find the frequency that maximizes the value of the Fourier transform. However, let us consider an analytical Fourier transform, of ##\sin\Omega t##. It's Fourier transform is given by $$-i\pi\delta(\Omega-\omega)+i\pi\delta(\omega+\Omega)$$ Normally, to find...
  42. P

    MHB Dharshan's question via email about a Laplace Transform

    $\displaystyle \begin{align*} \mathcal{L} \left\{ 5\sin{ \left( 11\,t \right) } \sinh{ \left( 11\,t \right) } \right\} &= \mathcal{L} \left\{ 5\sin{ \left( 11\,t \right) } \cdot \frac{1}{2} \left( \mathrm{e}^{11\,t} - \mathrm{e}^{-11\,t} \right) \right\} \\ &= \frac{5}{2} \,\mathcal{L} \left\{...
  43. Jason-Li

    Comp Sci Laplace Transform of the input portion of this circuit

    So I have completed (a) as this (original on the left): I have then went onto (b) and I have equated T(s)=Z(s) as follows: and due to hence Does this look correct to you smarter people? Thanks in advance! All replies are welcome :)
  44. arcTomato

    Engineering Fourier transform when the data is lacking datapoints

    I would like to know the equation of Fourier transform when the data has lack. like this sine wave.
  45. Fosheimdet

    A Fourier transform equation question

    In my QFT homework I was asked to prove that $$\int d^3x \int \frac{d^3k}{(2\pi)^3} e^{i\mathbf{k} \cdot (\mathbf{x} - \mathbf{y})} k_j f(\mathbf{x}) = i \frac{df}{dx_j}(\mathbf{y}) $$ Using ##\frac{\partial e^{i\mathbf{k} \cdot (\mathbf{x} - \mathbf{y})}}{\partial x^j} = i k_j e^{i\mathbf{k}...
  46. G

    MHB Laplace / inverse laplace transform

    Problem: Find a (limited?) solution to the diff eq. At the end of the solution, when you transform \frac{-1}{s+1} + \frac{2}{s-3} why doesn't it become -e^{-t} + 2e^{3t} , t>0 ?
  47. G

    MHB Fourier and inverse fourier transform

    Hi, I've been looking all over the net for good examples but I've only found some intro but no examples being solved. If you know of good resources (both theories and problems) please let me know! a) Calculate Fourier and inverse Fourier transform of f(t). b) Calculate the limit. My...
  48. G

    MHB Solve integral with laplace transform

    So the task is to solve the following integral with laplace transform. Since t>0 we can multiply both sides with heaviside stepfunction (lets call it \theta(t)). What I am unsure about is what happens with the integral part and how do we inpret the resulting expression? What will it result...
  49. S

    Compute the given Fourier transform by using the given tables

    Hello, everyone. :) I'm trying to do a certain problem regarding Fourier transforms (but one that's supposedly easy, because of just using tables, rather than fully computing stuff), and I know how to do it, but I don't know why it works. Here's the problem statement.: "Compute the Fourier...
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