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






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

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  1. O

    I Using Fourier Transform to Solve ODE with Initial Conditions

    Hi, let's take this ode: y''(t) = f(t),y(0)=0, y'(0)=0. using the FT it becomes: -w^2 Y(w) = F(w) Y(w)=( -1/w^2 )F(w) so i can say that -1/w^2 is the Fourier transorm of the green's function(let's call it G(w)). then y(t) = g(t) * f(t) where g(t) = F^-1 (G(w)) (inverse Fourier transorm) how can...
  2. A

    Fourier transform between variables of different domains

    I'm doing a research project over the summer, and need some help understanding how to construct an inverse Fourier transform (I have v. little prior experience with them). 1. Homework Statement I know the explicit form of ##q(x)##, where $$ q(x) = \frac{M}{2 \pi} \int _{- \infty}^{\infty} dz...
  3. J

    Solve Fourier Transform Homework: Wrong Answer?

    Homework Statement Homework Equations if x(t) --> X(W) then x(-t) --> X(-W) and x(t+a)-->ejwX(W) The Attempt at a Solution I'm getting right answer for 1st part. For second part book says right answer is C. Where am I wrong?[/B]
  4. E

    Python Fit_transform() vs. transform()

    Hi, I noticed that in some cases we first call fit_transform(), and afterwards we call transform(). Like in the following example: from sklearn.preprocessing import PolynomialFeatures X_train = np.array([6, 8, 10, 14, 18]).reshape(-1, 1) X_test = np.array([6, 8, 11, 16]).reshape(-1, 1)...
  5. Johny911

    Wave equation, separation of variables and the Laplace transform

    Homework Statement Homework Equations If i solve the wave equation using separation of variable and laplace tranform. Will i get the same answer ? The Attempt at a Solution
  6. S

    I Types of complex matrices, why only 3?

    Hi, the three main types of complex matrices are: 1. Hermitian, with only real eigenvalues 2. Skew-Hermitian , with only imaginary eigenvalues 3. Unitary, with only complex conjugates. Shouldn't there be a fourth type: 4. Non-unitary-non-hermitian, with one imaginary value (i.e. 3i) and a...
  7. H

    How to Express a Z-Transform as a Generating Function

    Homework Statement For example : How to inverse z-domain function (z2+3z+7)/(z2+4z+3) The Attempt at a Solution Whatever I use partial fraction to simply the z-domain function, I cannot continue the next step, such as 1/(z+3)
  8. A

    A Fourier Transform for 3rd kind of boundary conditions?

    I am studying online course notes from University of Waterloo on 'Analytical mathematics in geology' in which the author describes a 'modified Fourier transform' which can be used to incorporate 3rd kind of boundary conditions. The formula is ## \Gamma \small[ f(x) \small] = \bar{f}(a) =...
  9. C

    Engineering Laplace Transform on RC circuit

    Homework Statement Homework EquationsThe Attempt at a Solution I'm kind of lost now, how do I go about getting this into the right form for partial fraction exapnsion. And also what do I do with the V(0'). There was no information given about it.
  10. S

    How Does Increasing 'n' Affect the Cut-off Frequency 'k_cut' in DFT Analysis?

    Homework Statement I have this function ##f(\theta)=cos(n \ sin(\frac{\theta}{2})\pi)## and I need to take the discrete Fourier transform (DFT) numerically. I did so and I attached the result for ##\theta \in [0,2\pi)## and n =2,4,8,16,32, together with the function for a given n. I need to...
  11. S

    Discrete Fourier Transform in Python

    Homework Statement I need to calculate the derivative of a function using discrete Fourier transform (DFT). Below is a simplified version of my code (just for sin function) in python Homework Equations from __future__ import division import numpy as np from pylab import * pi = np.pi def...
  12. Milsomonk

    How does the determinant of the metric transform

    Homework Statement In special relativity the metric is invariant under lorentz transformations and therefore so is the determinant of the metric. How does the metric determinant transform under a more general transformation $$x^{a\prime}=J^{a\prime}_{\quad a}x^{a}$$ where $$J^{a\prime}_{\quad...
  13. Jonski

    Convolution - Fourier Transform

    Homework Statement An LTI system has an impulse response h(t) = e-|t| and input of x(t) = ejΩt Homework Equations Find y(t) the system output using convolution Find the dominant frequency and maximum value of y(t) Ω = 2rad/s The Attempt at a Solution I have tried using the Fourier transform...
  14. kaniello

    A Help with Discrete Sine Transform

    Hi, I am a neophyte in Discrete Fourier Transform and I am procticing with discrete Sine-transform. Specifically I want to calculate $$ \mathcal{F}_s \lbrace x \cdot e^{-x^2} \rbrace = \int\limits_{0}^{\infty } x \cdot e^{-x^2} \cdot \sin\left(x\right)\, \mathrm{d}x = \frac{1}{2} \pi^2 \omega...
  15. jdawg

    Laplace Transform with Imaginary Roots

    Homework Statement 4(d2x/dt2) +3x = t*e-3tsin(5t) Homework EquationsThe Attempt at a Solution So I know how to take the Laplace transform and find the function for the Laplace domain: X(s) = 10(s+3)/(((s+3)2+25)2)(4s2+3) + (10s/(4s2+3)) + (2/(4s2+3)) But trying to convert...
  16. F

    B Fourier Transform of Spacetime

    When you do a Fourier transform of spacetime.. what do you get? (or how does spacetime look in frequency domain? And what applications do this and what results are they looking or solving for?
  17. Telemachus

    Fortran Discrete Fast Fourier transform with FFTW in FORTRAN77

    Hi, this thread is an extension of this one: https://www.physicsforums.com/posts/5829265/ As I've realized that the problem is that I don't know how to properly use FFTW, from http://www.fftw.org. I am trying to calculate a derivative using FFTW. I have ##u(x)=e^{\sin(x)}##, so...
  18. Telemachus

    Doubt about a discrete Fourier Transform

    Hi. I was checking the library for the discrete Fourier transform, fftw. So, I was using a functition ##f(x)=sin(kx)##, which when transformed must give a delta function in k. When I transform, and then transform back, I effectively recover the function, so I think I am doing something right...
  19. PhysicsCollegeGirl

    Laplace transform (translation on the s-axis)

    Homework Statement L-1{[(2s-1)]/[(s^2)(s+1)^3]} Homework Equations L{f(t)e^(at)}=F(s-a) The Attempt at a Solution I have tried million ways but the different exponents in the denominator are throwing me off. The other problem is that I cannot use partial fractions, the homework instructions...
  20. D

    B Correctness of Equations in Electromagnetism Textbook

    Hello buddies! Please, check out these equations... Tell me, please, are they mathematically correct or not? I need a simple YES/NO answer. I have not sufficient knowledge to understand them. I just need to know whether they are correct... Thank you! P.S. Am is amplitude; I guess it is a...
  21. A

    Fourier Transform with inverse

    Homework Statement Q/ in this inverse Fourier problem, how did he come with the results of integration of (Sinc) function and how did he come up with those results of integration with the inverse part (as in the attached picture) here is the problem: https://i.imgur.com/Ir3TQIN.png Homework...
  22. A

    Understanding Fourier Transform: Solving a Homework Problem Step by Step

    Homework Statement Hello everyone, am trying to solve this Fourier Trans. problem, here is the original solution >> https://i.imgur.com/eJJ5FLF.pngQ/ How did he come up with this result and where is my mistake? Homework Equations All equation are in the above attached picture The Attempt at a...
  23. B

    I Fourier transform and locality/uncertainty

    Could you explain a bit about the relationship between locality and uncertainty in Fourier pairs? Many pages talk about uncertainty principle stating that the precision at which we can measure time duration of signal cannot unlimitedly grow without affecting precision on bandwidth. Many other...
  24. R

    Matching Discrete Fourier Transform (DFT) Pairs

    Homework Statement [/B] I am trying to match each of the following 28-point discrete-time signals with its DFT: Set #1: Set #2: Homework EquationsThe Attempt at a Solution Set #1 We have already established (here) that: ##Signal 1 \leftrightarrow DFT3## ##Signal 4 \leftrightarrow...
  25. A

    Fourier transform of the ground state hydrogen wave function

    Hi! 1. Homework Statement From the website http://www1.uprh.edu/rbaretti/MomentumspaceIntegration8feb2010.htm we can see the Fourier transform of the ground state hydrogenic wave function : Φ(p) = ∫ ∫ ∫ exp(-i p r) (Z3/π )1/2 exp(-Zr) sin(θ) dθ dφ r² dr (1.1) After intregation...
  26. R

    Discrete Fourier Transform (DFT) Matching

    Homework Statement Match each discrete-time signal with its DFT: Homework EquationsThe Attempt at a Solution I am mainly confused about Signal 7 and Signal 8. Signal 1 is the discrete equivalent to a constant function, therefore its DFT is an impulse (Dirac ##\delta##), so it corresponds...
  27. F

    Trouble with Galilean transform problem heat equation

    Homework Statement 1. The common form of the heat-diffusion equation governing the temperature distribution $$\rho C_p \frac{\partial T}{\partial t}=k\nabla^2T$$ Is this equation valid in any inertial frame of reference? (i.e. does it have the property of Galilean invariance?) If not, can it...
  28. Addez123

    Can't find inverse Z transform

    Homework Statement I got the laplace transfer function H(s) = 1/(s + 2) and I'm suppose to find the inverse Z transform by first converting to H(z) by s = Ts/2*(z-1)/(z+1) Then do inverse Z-transform using the "displacement rule" - Never heard of. Homework Equations H(s) = 1/(s + 2) s =...
  29. MattRob

    Showing that Metric Connections transform as a Connection

    Homework Statement Show that the metric connection transforms like a connection Homework Equations The metric connection is Γ^{a}_{bc} = \frac{1}{2} g^{ad} ( ∂_{b} g_{dc} + ∂_{c} g_{db} - ∂_{d} g_{bc} ) And of course, in the context of Einstein's GR, we have a symmetric connection, Γ^{a}_{bc}...
  30. S

    I Transform Bases for 4-Vectors in Ref. Frames

    Hello! Why do we need to impose a change on the basis vector, when going from a reference frame to another. I understand that the components of the vector and the basis change using inverse matrices (the components use a matrix and the vector basis the inverse). But the transformation condition...
  31. Vitani11

    Inverse Laplace transform for an irreducible quadratic?

    Homework Statement I have to take the inverse Laplace of this function (xoms+bxo)/(ms2+bs+k) this can not be broken into partial fractions because it just gives me the same thing I started with. How is this done? This is coming from the laplace of the position function for a harmonic oscillator...
  32. M

    Applying Convolution to a PDE with a Fourier Transform

    Homework Statement $$u_{xx}=u_t+u_x$$ subject to ##u(x,0)=f(x)## and ##u## and ##u_x## tend to 0 as ##x\to\pm\infty##. Homework Equations Fourier Transform The Attempt at a Solution Taking the Fourier transform of the PDE yields $$ (\omega^2-i\omega) F\{u\}=...
  33. M

    Integral of absolute value of a Fourier transform

    Homework Statement Hi guys, I am going to calculate the following integral: $$\int_0^{f_c+f_m} |Y(f)|^2\, df$$ where:$$Y(f)=\frac{\pi}{2} \alpha_m \sum_{l=1}^{L} \sqrt{g_l}\left [ e^{-j(\omega \tau_l - \theta_m)} \delta(\omega - \omega_0) + e^{-j(\omega \tau_l + \theta_m)} \delta(\omega +...
  34. G

    Laplace transform of derivative of convolution

    Prelude Consider the convolution h(t) of two function f(t) and g(t): $$h(t) = f(t) \ast g(t)=\int_0^t f(t-\tau) g(\tau) d \tau$$ then we know that by the properties of convolution $$\frac{d h(t)}{d t} = \frac{d f(t)}{d t} \ast g(t) = f(t) \ast \frac{d g(t)}{d t}$$ Intermezzo We also know that...
  35. entropy1

    I Why is momentum the Fourier transform of position?

    Apart from the fact that it is, what is the physical significance of the fact that you can get the momentum distribution of a particle by taking the Fourier transform of its position distribution?
  36. Vitani11

    Proving inverse Fourier transform of 1/(1+x^2) = 1/(1+x^2)

    Homework Statement F(t) = sqrt(π/2)e-t for t>0 F(t) = sqrt(π/2)et for t<0 In other words the question asks to solve this integral: 1/sqrt(2π) ∫F(t)eitxdt and show that it equals 1/(1+x2) Homework Equations F(t) = sqrt(π/2)e-t for t>0 F(t) = sqrt(π/2)et for t<0 1/sqrt(2π) ∫F(t)eitxdt The Attempt...
  37. Eclair_de_XII

    How to abstractly prove a Laplace transform identity?

    Homework Statement "Suppose that ##F(s) = L[f(t)]## exists for ##s > a ≥ 0##. (a) Show that if c is a positive constant, then ##L[f(ct)]=\frac{1}{c}F(\frac{s}{c})## Homework Equations ##L[f(t)]=\int_0^\infty f(t)e^{-st}dt## The Attempt at a Solution ##L[f(ct)]=\int_0^\infty f(ct)e^{-st}dt##...
  38. M

    I Truncated Fourier transform and power spectral density

    Hello, I am trying to find an expression for the signal-to-noise ratio of an oscillating signal on top some white noise. In particular I would like to know how the SNR scales with the integration time. It is well known that during some integration time ##T##, the SNR increases as ##T^{1/2}##...
  39. V

    Fourier transform of periodic potential in crystal lattice

    Homework Statement Homework Equations I'm not sure. The Attempt at a Solution I started on (i) -- this is where I've gotten so far. I am asked to compute the Fourier transform of a periodic potential, ##V(x)=\beta \cos(\frac{2\pi x}{a})## such that...
  40. Archie Medes

    Transform difference equation into continuous function?

    Homework Statement My question: Can I turn this difference equation for R below, into a continuous function R(t)? I have no idea if, or how, I can. And I'd like to. Equation derived from the following manufacturer statement on the thermal response of a thermistor to a fixed temperature: The...
  41. B

    B What Integral Transform is this?

    What is the transformation used Is there any explanation for : $$ \frac{\mathit{\lambda}}{\mathit{\Gamma}{\mathrm{(}}{q}{\mathrm{)}}}\mathop{\int}\limits_{t0}\limits^{t}{{\mathrm{(}}{t}\mathrm{{-}}{s}{\mathrm{)}}^{{q}\mathrm{{-}}{1}}}{x}_{0}\mathrm{(}s\mathrm{)}ds $$ How did become like this...
  42. L

    I Wave equation solution using Fourier Transform

    I'm studying Quantum Field Theory and the first example being given in the textbook is the massless Klein Gordon field whose equation is just the wave equation \Box \ \phi = 0. The only problem is that I'm not being able to get the same solution as the book. In the book the author states that...
  43. D

    I Transpose and Inverse of Lorentz Transform Matrix

    Let ##\Lambda## be a Lorentz transformation. The matrix representing the Lorentz transformation is written as ##\Lambda^\mu{}_\nu##, the first index referring to the rows and the second index referring to columns. The defining relation (necessary and sufficient) for Lorentz transforms is...
  44. M

    Calculating Magnetic Field from FFT Amplitude

    So a little bit of background: I work in an undergraduate lab at UMass Amherst and am currently building/optimizing a faraday magnetometer for use in the Muon g-2 experiment at Fermilab. The magnetometer works as follows. A laser is shone through a crystal with a particular Verdet Constant at...
  45. T

    I Help with infinitesimal transformation to finite transform

    <Moderation note: edited LaTex code> E.g. A rotation by a finite angle θ is constructed as n consecutive rotations by θ/n each and taking the limit n→∞. $$ \begin{pmatrix} x' \\ y' \\ \end{pmatrix} =\lim_{x \to \infty} (I + \frac{\theta}{n} L_z )^n \begin{pmatrix} x...
  46. P

    I Can Least Squares Solve for Rigid Transform?

    Background: I have a set of known 3D feature points {x_i} on the surface of an object in some reference position/orientation at time t = 0. At t > 0 the object will have moved by a rigid transform. I am using computer vision to estimate the position of the 3D feature points {y_i}. I want to...
  47. P

    Find equation obeyed following Fourier transform

    Homework Statement I have a potential V(x,t) = scos(ωt)δ(x) where s is the strength of the potential. I need to find the equations obeyed by φn given that ## \psi_E (x,t) =\phi_E exp[\frac{-iEt}{\hbar}] \\ \phi_E (x, t + T) = \phi_E (x,t)\\ \phi_E =...
  48. cg78ithaca

    A Inverse Laplace transform of a piecewise defined function

    I understand the conditions for the existence of the inverse Laplace transforms are $$\lim_{s\to\infty}F(s) = 0$$ and $$ \lim_{s\to\infty}(sF(s))<\infty. $$ I am interested in finding the inverse Laplace transform of a piecewise defined function defined, such as $$F(s) =\begin{cases} 1-s...
  49. cg78ithaca

    A Inverse Laplace transform of F(s)=exp(-as) as delta(t-a)

    This is mostly a procedural question regarding how to evaluate a Bromwich integral in a case that should be simple. I'm looking at determining the inverse Laplace transform of a simple exponential F(s)=exp(-as), a>0. It is known that in this case f(t) = delta(t-a). Using the Bromwich formula...
  50. D

    Fourier Transform of Polarization

    Homework Statement The problem is from an optics text, however I believe the problem to be a mathematical one. I'm trying to take the Fourier transform of P(t) = ε0∫ X(t-τ)E(τ) dτ which should equal P(ω) = ε0X(ω)E(ω) where ε0 is a constant X is the susceptibility E is the...
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