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
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=



0





f
(
t
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e


s
t



d
t
.


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

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  1. 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...
  2. I

    Fourier transform of the linear function

    Hello, I was wondering if one can give meaning to the Fourier transform of the linear function: \int_{-\infty}^{+\infty} x e^{ikx}\, dx I found that it is \frac{\delta(k)}{ik} , does this make sense?
  3. binbagsss

    Sin/cos integrals multiplying results (fourier transform).

    Okay, I am trying to determine the Fourier transform of cos (2\pix)=f(x) Where F(k)=^{\infty}_{\infty}\intf(x)exp^{-ikx} dx, So I use eulers relation to express the exponential term in terms of cos and sin, and then I want to use sin/cos multiplication integral results, such as...
  4. A

    Laplace transform initial value problem-

    Laplace transform initial value problem--need help! Looking at the solutions to these initial value problems, I am very confused as to how the highlighted steps are derived (both use heaviside step functions). I know the goal is to get the fractions in a familiar form so that one can look them...
  5. A

    Fourier transform of sinusoidal functions

    Homework Statement Homework Equations sinc(x) = \frac{sin(x)}{x} The Attempt at a Solution bit unsure how to get started?? i know transform of rectangular pulse pτ(t)=τ*sinc(τω/2∏) also that sin(ωt)= ejωt-e-jωt / (2) I could also probably sketch sinc(t/2∏), if that helps.
  6. B

    Fourier transform of multivalued functions

    Dear all, I have recently come across the following Fourier transform (FT): I=\int_{-\infty}^{\infty} dx \, e^{-\imath x t} \frac{(1-x^2)}{(1+x^2)^{3/2} (a^2+x^2)}. The integrand contains two branch points on the imaginary axis, plus two poles also residing on the imaginary...
  7. polygamma

    MHB Evaluating an Integral: Laplace Transform Method

    The typical way to evaluate $ \displaystyle \int_{0}^{\infty} \frac{\cos mx}{a^{2}+x^{2}} \ dx$ is by contour integration. In a recent thread I evaluated that integral using the Laplace transform. http://mathhelpboards.com/analysis-50/advanced-integration-problem-9129.html#post42551My...
  8. T

    How Does the Hankel Transform Solve Problems in Cylindrical Domains?

    Hello, As of recently, I've been working with Laplace transforms and have a question about their relationship to solving differential equations. I know the definition of the laplace transform and I know that a function is essentially being transformed from the time domain to complex...
  9. B

    Fourier transform and the frequency domain

    I understand that the Fourier transform maps one function onto another. So it is a mapping from one function space onto another. My question is, why is it often referred to as a mapping from time domain to the frequency domain? I don't understand why the image of the Fourier transform...
  10. T

    Arranging this expression into a laplace transform

    Hi Guys, I have an expression that i am struggling to manipulate into a laplace transform. This expression should fit one or a combination of the common transform pairs. I believe the transform the expression should be fitting is either a unit step 1/s a unit ramp 1/s^2 an exponential 1/s+a...
  11. B

    Any suggestions for finding the inverse Laplace transform of 11/(s^2+16)^2?

    Hi, I would like to find the inverse Laplace transform for 11/(s^2+16)^2 I have tried to expand it using the following partial fraction decomp to find the constants and take the inverse Laplace but this did not work C1(s)+ C2/(s^2+16) + C3(s)+C4/(s^2+16)^2 Does anyone have any suggestions?
  12. B

    Laplace transform with 2s(s^2+9) in denominator

    Homework Statement Hi I would like to know how to expand 20/2s(s^2+9) in order to find the inverse Laplace Transform of the function K(s) to gt k(t). The (s^2+9) term in the denominator is throwing my calculations off for the constants because of the s^2 term. Homework Equations...
  13. B

    Laplace Transform for shifted Unit Step Function

    Hello, I have a relatively simple question. after being unable to find it through google I have decided to ask you guys if you know what the Laplace transform of a unit step function that looks like this would look like Us(t-2) From tables, the Laplace transform for a regular units step...
  14. T

    Fourier transform of an annulus

    Hi guys, I've been using this site for a while now, but this is going to be my first post. I want to pick your brains to get some insight on this problem I'm tackling. I'm trying to take a Fourier Transform of a function. My function is a function of (r,phi) and it is a piecewise function...
  15. Philosophaie

    Transform from one position to another.

    Homework Statement Using the Schwarzschild Metric and the Contravariant Position Vector 1x4 ##x^k## with 4 vector: $$x^{k'} = \left[ \begin {array}{c}r \\ \theta \\ \phi \\ t \end {array} \right]$$ where ##x^1## = r = 1 per unit distance ##x^2## = ##\theta## = 50 Degrees ##x^3##...
  16. G

    Inverse Laplace Transform Help

    Homework Statement Is there a way to evaluate L^{-1}(\frac{F(s)}{s + a})? I'm sure if it can be evaluate. Homework Equations The Attempt at a Solution
  17. D

    MHB Laplace Transform with two steps

    Given the transfer function \[ H(s) = \frac{Y(s)}{U(s)} = \frac{1}{s + 1} \] and \[ u(t) = 1(t) + 1(t - 1). \] How do I find U(s)? I know I take the Laplace transform of u(t) but with the two step functions how can this be done? The Laplace transform of the step function is \(\frac{1}{s}\)...
  18. D

    MHB Inverse Laplace Transform problem

    I can't seem to part of an inverse Laplace transform correct. \begin{align*} f(t) &= \frac{6}{5}\mathcal{L}^{-1}\bigg\{\frac{1}{s + 2}\bigg\} + \frac{3}{5}\mathcal{L}^{-1}\bigg\{\frac{3s - 1}...
  19. G

    Laplace Transform Within a Domain

    Homework Statement Find the Laplace transform of f(t) = t \forall 0≤t≤T, 0 otherwise Homework Equations The Attempt at a Solution I write the function as tu(t)-t*u(t-T) That is turn on the function t at t=0 and turn the function t off at t=T. It seems to be right to me...
  20. D

    Solve a Laplace transform puzzle

    Hi~ I recently solve a Laplace transform problem as following L[int{t,0}cosh(t'-1)U(t'-1)dt']=? U(t'-1) is the unit step function(=1 for t'>1, =zero otherwise) According the standard Laplace formula : (1)L[cosh(t-1)U(t-1)]=exp(-s)*s/(s^2-1); (2)L(int{t,0}f(t')dt')=F(s)/s...
  21. I

    Fourier transform of a functional

    Hello, I was wondering if such a thing even exists, so here it goes... Let's say I have a function x(s) (it is real, smooth, differentiable, etc.) defined on (0,1). In addition, dx/ds = 0 on the boundary (s=0 and s=1). I can compute its Fourier transform (?) as a_p = \int_0^1 x(s)...
  22. V

    Fourier Transform of Distribution

    Hi, I hope somebody can help me with this one. Homework Statement Compute the Fourier Transform of the distribution x-a Homework Equations The Fourier Transform of a distribution is just the distribution evaluated with the Fourier Transform of a test function.The Attempt at a Solution See...
  23. A

    Fourier Transform: Determining Constant in Convolution

    I have an exercise with a function of the form: h(t) = f(t)g(t) and f(t) and g(t) both have discrete Fourier series, which implies that h does too. I want to find the Fourier series of h, so my teacher said I should apply the convolution theorem which would turn the product above into a...
  24. I

    Trouble with Laplace transform of a function

    I have a probability distribution as follows: \begin{equation}p_j(t)=\frac{1}{N^2}\left|\sum_{k=0}^{N-1}c_{1,k}e^{ij\tilde{k}}\right|^2+\frac{1}{N^2}\left|\sum_{k=0}^{N-1}c_{2,k}(t)e^{ij\tilde{k}}\right|^2\end{equation} where...
  25. U

    Solving DE using Fourier Transform

    Homework Statement Part (a): State inverse Fourier transform. Show Fourier transform is: Part (b): Show Fourier transform is: Part (c): By transforming LHS and RHS, show the solution is: Part(d): Using inverse Fourier transform, find an expression for T(x,t) Homework Equations The Attempt...
  26. alyafey22

    MHB What is the relationship between the Mellin transform and the sine function?

    Mellin transform of sine Define the Mellin transform as \mathcal{MT}\{f(t)\}=\int^\infty_0 t^{z-1} f(t) dt where z\in \mathbb{C}If the transform exists , it is analytic in some vertical strip a<\mathrm{Re}(z)<b in the complex plane Find the vertical strip of \mathcal{MT}\{ \sin(t)\}...
  27. alyafey22

    MHB Existence of Laplace transform

    Prove the following Suppose that $f$ is piecewise continuous on [0,\infty) and of exponential order $c$ then \int^\infty_0 e^{-st} f(t)\, dt is analytic in the right half-plane for \mathrm{Re}(s)>c
  28. evinda

    MHB What are the restrictions for s and how to find them in Laplace transform?

    Hello! :D I have to find the solution of the equation y'(x)+5y(x)=e^{-x} , 0<x<\infty , y(0)=2 , using the Laplace transform. That's what I have done so far: $$L\{y'(x)+5y(x)\}=L\{e^{-x}\}$$ $$L\{y'(x)\}+5L\{y(x)\}=L\{e^{-x}\}$$ $$sY(s)-y(0)+5Y(s)=\frac{1}{s+1}$$...
  29. P

    Solving Integral Using Laplace Transform

    I posted this in the homework section, but I haven't received any help, so hopefully putting it in this section won't be an issue. I'm trying to compute the integral $$ \int_0^ \infty \frac{ \cos xt}{1 + t^2} \, dt $$ using the Laplace transform. The first thing that catches my eye is the 1...
  30. P

    What is the Laplace Transform Integral for the function $\frac{\cos xt}{1+t^2}$?

    Homework Statement $$ \int_0^\infty \frac{\sin xt}{x} \, dt $$ Homework Equations The Attempt at a Solution $$ = \int_0^\infty L(\sin xt) \, dp $$ $$ = \int_0^\infty \frac{x}{p^2 + x^2} \, dp $$ $$ = x \int_0^\infty \frac{dx}{p^2 + x^2} \, dp $$ p = x tan theta: $$ = x \int_0^{\pi/2}...
  31. P

    Question: How do we use the Laplace transform to find the inverse of a function?

    Homework Statement Find $$ L^{-1} \left[ \frac{1}{ (p^2 + a^2)^2} \right] $$ Homework Equations $$ L [ x \cos ax ] = \frac{p^2 - a^2} { (p^2 + a^2) ^2 } $$ The Attempt at a Solution I have no idea. Any thoughts?
  32. A

    How Do Delta Functions Simplify the Fourier Transform in Quantum Mechanics?

    Homework Statement The exercise is a) in the attached trial. I have attached my attempt at a solution, but there are some issues. First of all: Isn't the example result wrong? As I demonstrate you get a delta function which yields the sum I have written (as far as I can see), not the sum...
  33. J

    Correcting a Laplace Transform Problem

    Homework Statement Why I am getting wrong answer related to this Laplace Transforms problem? According to the book "Higher Engineering Mathematics 6th edition by John O Bird" page no. 583 one should get (e^{-st}/(s^{2} + a^{2}))(a sin at - s cos at)Homework Equations ∫e^{-st}cos at dt The...
  34. J

    Airy integral by Fourier transform?

    http://calclab.math.tamu.edu/~fulling/m412/f07/airywkb.pdf Can someone walk me through this derivation of the Airy integral by Fourier transform? I have tried it but failed
  35. R

    Software to transform sentences

    I want to build some software that will transform a formal language from one set of symbols to another. What would be the best software to do that with. Here is one example of what I want to do: Say we have (x'Hy) BC (x'Hz) I need an algorithm to transform that into: ((w'Hp) IDx'-z) A...
  36. M

    How do the Maxwell equations transform under a time reversal?

    Guys, Let me ask you the silliest question of the year. I am looking at the Maxwell equations in their standard form. No 4-dim potential A, no Faraday tensor F, no mentioning of special relativity - just the standard form from a college-level textbook. I know that the eqns are NOT...
  37. T

    Correct way for symmetry transform

    Homework Statement Hi I'm trying to understand how symmetry transform works. Suppose a lagrangian L = q^{-2} (actually it had another kinetic member, but I don't need it for my question here) The matching action S = \int dt q^{-2} We were told that it has the next symmetry t...
  38. M

    Time-independence of original coordinates in canonical transform

    I am going through my professors notes on generating functions. I come across the following equation: \frac{\partial}{\partial t} \frac{\partial F}{\partial \xi^k} = \frac{\partial}{\partial t} \left( \gamma_{il} \frac{\partial \eta^i}{\partial \xi^k}\eta^l - \gamma_{kl}\xi^l \right ). Here...
  39. E

    Unitary discrete Fourier transform

    I'm trying to prove that the discrete form of the Fourier transform is a unitary transformation So I used the equation for the discrete Fourier transform: ##y_k=\frac{1}{\sqrt{N}}\sum^{N-1}_{j=0}{x_je^{i2\pi\frac{jk}{N}}}## and I put the Fourier transform into a N-1 by N-1 matrix form...
  40. N

    Do Fourier transforms always converge to 0 at the extreme ends?

    From -infinity to infinity at the extreme ends do Fourier transforms always converge to 0? I know in the case of signals, you can never have an infinite signal so it does go to 0, but speaking in general if you are taking the Fourier transform of f(x) If you do integration by parts, you get a...
  41. I

    Laplace Transform IVP (Easy I think)

    Homework Statement Use Laplace transforms to solve the initial value problems. ##y''+4y=0;## ##y(0)=5;## ##y'(0)=0## Homework Equations The Attempt at a Solution $$y''+4y=0$$ $$L(y'')+L(4y)=L(0)\implies s^{2}Y(s)-sy(0)-y'(0)+4(sY(s)-y(0))=0\implies s^{2}Y(s)+4sY(s)-5s-20=0$$...
  42. B

    Final value theorems to each transform pair

    Homework Statement Find f(t) for the function F(s)=(10s^2+85s+95)/(s^2+6s+5) and apply the initial and final value theorems to each transform pairHomework Equations Initial value theorem: f(0)=lim s->∞ s(F(s)) Final value theorem: f(∞) = lim s->0 s(F(s))The Attempt at a Solution After dividing...
  43. J

    MHB Matrix transform- about origin, then angular rotation

    The problem asks to find the standard matrix for the composition of these two linear operations on R2. - A reflection about the line y=x, followed by a rotation counterclockwise of 60o. This is how I proceeded. y=x $\begin{bmatrix}0&1\\1&0 \end{bmatrix}$ counter clockwise 60degs...
  44. C

    Efficient Computation of Convolution using Z-Transform in Discrete-Time Signals

    x_1(n) = (!/4)^n u(n-1) and x_2(n) = [1- (1/2)^n] u(n) X_1(z) = (1/4)z^-1 / (1-(!/4)z^-1 and X_2(z) = 1/(1-z^-1) + 1/(1-(1/2)z^-1) Y(z) = X_1(z) X_2(z) = (-4/3) /(1-(1/4)z^-1 + (1/3) / (1-z^-1) + 1/(1-(1/2)z^-1
  45. T

    Laplace Transform Solution to Second Order ODE IVP

    Homework Statement y''+6y=f(t), y(0)=0, y'(0)=-2 f(t)= t for 0≤t<1 and 0 for t≥1 Homework Equations The Attempt at a Solution L{y''}+6L{y}=L{t}-L{tμ(t-1)} where μ(t-1) is Unit Step Y(s)=L{y} sY(s)-y(0)=L{y'} and y(0)=0 s2Y(s)-sy(0)-y'(0)+6Y(s) where y(0)=0 and...
  46. 1

    Inverse Laplace Transform of s/(s^2+1)^2)

    Homework Statement ##\mathcal{L}^{-1}\Big\{\frac{s}{(s^2+1)^2}\Big\}## I'm trying to figure out how to find the inverse Laplace transform of this expression. Is this something you just look up in a table or is there a way to find it directly, maybe by Convolution?
  47. B

    Fourier transform of single pulse & sequence of pulses

    Homework Statement What is the Fourier transform of a single short pulse and of a sequence of pulses? The Attempt at a Solution In class we haven't dealt with the mathematics of a Fourier transform, however my professor has simple stated that a Fourier transform is simply a equation...
  48. L

    Laplace transform interpretation

    Hello, We were introduced to Laplace transforms in my ODE class a few days ago, so naturally I went online to try to figure out what this transform actually is, rather than being satisfied with being able to compute simple Laplace transforms. The Wikipedia page for the transform says it...
  49. S

    Applying the fourier transform to a PDE

    I have a tutorial question for maths involving the heat equation and Fourier transform. {\frac{∂u}{∂t}} = {\frac{∂^2u}{∂x^2}} you are given the initial condition: u(x,0) = 70e^{-{\frac{1}{2}}{x^2}} the answer is: u(x,t) = {\frac{70}{\sqrt{1+2t}}}{e^{-{\frac{x^2}{2+4t}}}} In this course...
  50. I

    Laplace Transform of t: Using Integration by Parts

    Homework Statement Apply the definition in (1) to find directly the Laplace transforms of the functions described (by formula or graph). 1) f(t)=t Homework Equations The Attempt at a Solution Seems pretty easy... Question is, I don't understand the directions exactly.. Am I...
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