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. R

    Inverse Laplace Transform of (1/(s+s^3))?

    Homework Statement What is the inverse laplace transform of (1/(s+s^3))? Homework Equations The Attempt at a Solution I looked it up on wolframalpha and got 1-cos(t), but I don't understand how they got that answer. I looked up a basic laplace transform chart and didn't see anything...
  2. A

    What is negative frequency(fourier transform)

    in Fourier transforms of normal baseband sigal , spectral components are replicated on both +ve and -ve sides of frequency axis. i know that both -ve and +ve frequency components contribute to the total power of the signal but i don't know the physical significance of the -ve frequencies...
  3. D

    MHB Correcting Constants in Convolution of Fourier Transforms

    I am trying to prove the convolution of the Fourier Transform $$ (\widehat{f\star g})(\xi) = 2\pi\hat{f}(\xi)\hat{g}(\xi) $$
  4. Jalo

    Fourier transform of a function

    Homework Statement a) Find the Fourier transform of the function f(x) defined as: f(x) = 1-3|x| , |x|<2 and 0 for |x|>2 b) Find the values of the inverse Fourier transform of the function F(k) obtained in a) Homework Equations F(k) = \frac{1}{\sqrt{2π}}\int f(t) eikx dx f(x) =...
  5. J

    Why complex discrete Fourier transform?

    I've been trying to figure out why it's standard to use complex discrete Fourier transforms instead of just the real version. It's discussed a bit here. http://dsp.stackexchange.com/questions/1406/real-discrete-fourier-transform As far as I can tell there's a hypothetical efficiency...
  6. M

    How to find inverse Laplace transform?

    Homework Statement Find inverse Laplace transform \mathcal {L}^{-1}[\frac{1}{(s^2+a^2)^2}]Homework Equations The Attempt at a Solution I try with theorem \mathcal{L}[f(t)*g(t)]=F(s)G(s) So this is some multiple of \mathcal{L}[\sin at*\sin at] So \mathcal {L}^{-1}[\frac{1}{(s^2+a^2)^2}]=\propto...
  7. M

    Laplace Transform of the product of two functions

    Hello, I am trying to figure out in my notes how my professor did L[(e^-3t)(sin2t)] = 2/(s+3)^2 +4 I think she just did it in her head and wrote it, so I don't actually know how to solve it. I am looking at my table of laplace transforms and there is none for a product of an exponential and...
  8. A

    Fourier Transform: Limit in Infinity of Exponential Function

    In calculating some basic Fourier transform I seem stumble on the proble that I don't know how to take the limit in infinity of an exponentialfunction with imaginary exponent. In the attached example it just seems to give zero but I don't know what asserts this property. I would have thought...
  9. fluidistic

    Infinite series, probably related to Fourier transform?

    Homework Statement A function f(x) has the following series expansion: ##f(x)=\sum _{n=0}^\infty \frac{c_n x^n}{n!}##. Write down the function ##g(y)=\sum _{n=0}^\infty c_n y^n## under a closed form in function of f(x). Homework Equations Not sure at all. The Attempt at a Solution...
  10. G

    Solving Laplace Transform: Need Help

    I'm having trouble with this question. Can anyone please guide me. My Attempt : = 1/(s-1) * L{t^2*e^-t} = 1/(s-1) * (2/(s+1)^3) = 2/((s-1)(s+1)^3)) but that's not the answer , its 2/((s-1) s^3) somehow. The question is attached below.
  11. T

    Finding the inverse laplace transform of (2/(s+2)^4) using Convolution theorem.

    Homework Statement Find the inverse laplace transform of (2/(s+2)^4) using the given table of identities: Homework Equations Here are the given identities: The Attempt at a Solution Alright, I realize that there is a simple identity that I can use with a factorial symbol, but this...
  12. A

    How to transform 2vdc to 240vac

    i have just recently discovered peltier devices which make electricity from the Seebeck effect. one video on you tube showing peltier device producing about 2 volts from a flame. i would like to know how to convert this 2 volts DC (if it is actually dc) into 2 volts AC then put it through a step...
  13. M

    Fourier Transform of a Gaussian With Non-Zero Mean

    Homework Statement I am looking at finding the Fourier transform of: f(t)=\exp \left[ \frac{-(t-m)^2}{2 \sigma^2}\right] Homework Equations \hat{f}(t)=\frac{1}{\sqrt{2 \pi}} \int_{-\infty}^{\infty} f(t) e^{-i \omega t} dt The Attempt at a Solution I did it a little differently that my...
  14. C

    MHB David's Fourier Transform Problem from YAnswers

    Here's my problem;Find the Fourier transform \(P(\omega)\) of the function;\[ p(t)=\left\lbrace \begin{array}{ll} e^{-9t} & \text{for } t \ge 0 \\ e^{9t} & \text{for } t \lt 0 \end{array} \right.\]Hence (use one of the shift theorems) find the inverse Fourier transform of; \(...
  15. D

    Series form of the Laplace transform

    I thought it would be obvious, but I can't find a series representation of the Laplace transform. I'm looking for something analogous to the Fourier series and how it can be used to derive the Fourier transform. I though it would simply be f(x) = \sum_{s=-\infty}^{\infty}{C_{s} e^{sx}} , but...
  16. E

    ROC and its relation to the inverse Laplace transform

    This is a conceptual question on the region of convergence (ROC) and the inverse Laplace transform (ILT). Here the bilateral laplace transform (LT) and the ILT are given by F(s)=L\{f(t)\}=\int_{-\infty}^{+\infty} f(t) e^{-st} dt and f(t)=L^{-1}\{F(s)\}=\frac{1}{i...
  17. H

    Fourier transform, Fourer Integral transform

    I was going to post this in the learning material section but i didnt have access to it for some reason. but i guess i can post it here. its homework after all. so i have noticed that there is almost nothing learning material on fourer transform on the web. like how to transform a function to...
  18. L

    Intuition about definition of laplace transform

    why was laplace transform developed i have googled it and found that it is something about shaping a family of exponential and vector projections etc i couldn't get it. some simply said that it was used to make a linear differential equation to algebraic equation but i couldn't understand how...
  19. N

    Laplace transform of the dirac delta function

    Homework Statement L[t^{2} - t^{2}δ(t-1)] Homework Equations L[ t^{n}f(t)] = (-1^{n}) \frac{d^{n}}{ds^{n}} L[f(t)] L[δ-t] = e^-ts The Attempt at a Solution My teacher wrote \frac{2}{s^{3}} -e^{s} as the answer. I got \frac{2}{s^{3}} + \frac{e^-s}{s} + 2 \frac{e^-s}{s^2} + \frac{2e^-s}{s^3}
  20. F

    How to transform non-linear frequency vibration to constant frequency?

    How to transform non-linear frequency vibration to constant frequency of vibration of 2 Hz? Such as transform the different frequency of waves to constant frequency and then maintain it..
  21. S

    Reference or explanation of zeta mellin transform in critical strip

    Hi. In Apostol's book "Introduction to analytic number theory", Teorem 3.2(b), Apostol proves (1) \zeta (s) = \lim\limits_{x \to \infty} \left\{ \sum\limits_{n \leq x} \frac{1}{n^s} - \frac{x^{1-s}}{1-s} \right\} for s in critical strip. I know this translates to a Mellin transform...
  22. L

    Laplace transform of a function squared, help with this system

    Homework Statement Use Laplace transform to the system: \frac{dy}{dt} + 6y = \frac{dx}{dt}3x - \frac{dx}{dt} = 2\frac{dy}{dt} x(0) = 2 ; y(0) = 3 The Attempt at a Solution I've tried everything on this one. I first solved \frac{dy}{dt} + 6y = 2\frac{dy}{dt} and I got y = 3e^{6t} ...
  23. fluidistic

    An integral arising from the inverse Fourier transform

    Homework Statement For a physics problem I must take the inverse Fourier transform of 2 functions. Namely I must compute the integral ##\frac{1}{\sqrt{2\pi}}\int_{-\infty} ^\infty [A\cos (ckt)+B\sin (ckt)]e^{ikx}dk##.Homework Equations Already given. i is the complex number. t is greater or...
  24. fluidistic

    Heat equation with Laplace transform

    Homework Statement Problem 8-19 in Matthews and Walker's book on mathematical physics. A straight wire of radius a is immersed in an infinite volume of liquid. Initially the wire and the liquid have temperature T=0. At time t=0, the wire is suddenly raised to temperature ##T_0## and...
  25. fluidistic

    Laplace transform to solve an ODE

    Homework Statement I must solve the following diff. eq. ##tx''-(4t+1)x'+(4t+2)x=0## with the initial condition ##x(0)=0## and the relations ##\mathcal {L }[tx]=-\frac{d \mathcal{L}[x]}{ds}##, ##\mathcal {L} [tx']=-\frac{d [s \mathcal {L}[x]]}{ds}## and ##\mathcal{L}[x']=s \mathcal...
  26. E

    Solving a Second Order Differential Equation with Laplace Transform

    Homework Statement this one stumped me.. d^2y/dt^2 +ωy=ksin((√ω)t) y(∏/4)=0, y'(∏/4)=0 The Attempt at a Solution → (s^2 + ω)U(s)= LT {ksin((√ω)(T+∏/4)} is as far as i can get (i know what to do with the left hand side once i get the LT of the right hand side but i don't know what to do with...
  27. H

    Unilateral and Bilateral Laplace Transform in Solving Differential Equations

    Why is it that the unilateral lateral Laplace transform is used when given initial conditions that are non-zero. Is there a reason that explains why it would be wrong to use the bilateral Laplace transform instead? I know bilateral does not have any input of initial conditions but that does not...
  28. M

    Are Laplace Transform Limits Equivalent to a Limit at Infinity?

    How we get relation \lim_{t\to 0}f(t)=\lim_{p\to \infty}pF(p)? Where ##\mathcal{L}\{f\}=F##.
  29. D

    Laplace Transform of Delta Function

    Homework Statement Evaluate the Laplace transform: L{δ(t-∏)tan(t)} Homework Equations The Attempt at a Solution L{δ(t-∏)tan(t)} = ∫ δ(t-∏)tan(t) dt evaluated from 0 to ∞ =tan(∏)e-∏*s = 0 Could someone check my work on this one? I'm suspicious that my transform is just zero...
  30. N

    Using Laplace Transform to solve a differential equation

    Homework Statement y" + y = 4δ(t-2π); y(0)=1, y'(0)=0 Homework Equations L[f(t-a) U(t-a)] = e^{-as} L[f(t)] L[δ(t-c)] = e^{-cs} The Attempt at a Solution My answer is: cos(t) + 4U(t-2π)sin(t-2π). When I used Wolframalpha it gave me 4sin(t)U(t-2π) + cos(t)
  31. T

    Magnitude in frequency domain of Fourier Transform

    Homework Statement Hi All, I'm just trying to practice graphing signals in frequency domain and I came across a stiuation I wasn't familiar with. If the exp() has a constant*t in it I'm not sure how to graph it, I remember that just cos it like a double sided exp(jwt) but with half the...
  32. W

    Evaluating a Fourier Transform Integral

    Evaluating a "Fourier Transform" Integral Homework Statement Evaluate I = ∫[0,∞] e-ktw2 cos(wx) dw in the following way: Determine ∂I/∂x, then integrate by parts. Homework Equations Possibly? The Attempt at a Solution Since integral limits do not depend on x, the partial with respect...
  33. F

    Laplace transform, sum of dirac delta

    Homework Statement Homework Equations I really wish they existed in my notes! *cry*. All I can think of is that integrating or in other words summing the dirac delta functions for all t, would be infinite? None the less the laplace transform exist since its asked for in the question and i...
  34. T

    Magnitude in frequency domain of Fourier Transform situation

    Hi All, I'm just trying to practice graphing signals in frequency domain and I came across a stiuation I wasn't familiar with. If the exp() has a constant*t in it I'm not sure how to graph it, I remember that just cos it like a double sided exp(jwt) but with half the magnitude. I've attached a...
  35. J

    Fourier transform from k-space to x

    I have calculated a k-space function to be f(k) = \frac{1}{2k} I want to Fourier transform this to find f(x), I have found many different Fourier transform equations...can I use this one? f(x) = \frac{1}{\sqrt{2π}}\int\frac{1}{2k}e-ikxdk Limits fo integration -Infinity to Infinity...
  36. J

    Help finding Fourier Transform

    Homework Statement Find the Fourier Transform of: f(t)=\frac{cos(\alpha t)}{t^2+\beta^2} Homework Equations F(\omega)=\frac{1}{2\pi}\int^{∞}_{-∞}\frac{cos(\alpha t)exp(i \omega t)}{t^2+\beta^2} The Attempt at a Solution I start with: cos(\alpha t)=\frac{exp(i \alpha t)+exp(-i...
  37. D

    Fourier transform pair for u(t)

    Homework Statement Ok I know Fourier transform pair for u(t) is pi*del(w)+1/(j*w) Am I right to say the transform pair of u(t)-u(t-1) is [pi*del(w)+1/(j*w)]-[pi*del(w-1)+1/(j*(w-1)] If not what is it? thanks
  38. chisigma

    MHB A Laplace Transform: Integral Calculation

    On MHF... Integral Caculation ... the user widapol did have some difficulties in the computation of the integral... $\displaystyle \int_{0}^{\infty} \ln^{2} (1+t)\ e^{- s t}\ dt$ (1) ... which of course is the L-Transform of the function $\displaystyle \ln^{2} (1+t)$. Remembering thye basic...
  39. G

    Discrete Fourier transform in k and 1/k

    Say you have some function that is periodic in a parameter k. The discrete Fourier transform from a sampling may be found in the usual way, giving the frequency spectrum in k. But what if I want to find the frequency spectrum in 1/k ? I'm not really sure what this is called, and so I've had a...
  40. fluidistic

    Calculating the Laplace transform of a Bessel function

    Homework Statement Hi guys! I'm basically stuck at "starting" (ouch!) on the following problem: Using the integral representation of the Bessel function J_0 (x)=\frac{1}{\pi} \int _0 ^\pi \cos ( x\sin \theta ) d \theta, find its Laplace transform. Homework Equations \mathbb{L}...
  41. A

    Fourier Transform - Solving for Impulse Response

    Homework Statement I'm trying to Solve for an impulse response h(t) Given the excitation signal x(t) and the output signal y(t) x(t) = 4rect(t/2) y(t) = 10[(1-e-(t+1))u(t+1) - (1-e-(t-1))u(t-1)] h(t) = ? y(t) = h(t)*x(t) --> '*' meaning convolution! I am unsure how to take the Fourier...
  42. fluidistic

    Laplace transform of a piecewise function

    Homework Statement I must calculate the Laplace transform of the following function: f(x)=1 for x \in [0,1] \cap [2,3] \cap [4,5] \cap ... , f(x)=0 otherwise. Homework Equations The Laplace transform is \mathbb{L} [f(x)]=\int _0 ^{\infty} e^{-sx}f(x)dx. The Attempt at a Solution...
  43. V

    Second fundamental theorem of calculus viewed as a transform?

    You see this picture of the second fundamental theorem of calculus and you are taught in high school / early college calculus that the t is a dummy variable. However, couldn't you view this as some sort of transform? You convert a function f(t) into a function of f(x). Is this a valid way to...
  44. M

    Laplace transform converge

    ##\mathcal{L}\{f(t)\}=F(s)## \mathcal{L}\{e^{at}\}=\frac{1}{s-a},Re(s)>a \mathcal{L}\{\sin (at)\}=\frac{a}{s^2+a^2}, \quad Re(s)>0 \mathcal{L}\{\cos (at)\}=\frac{s}{s^2+a^2},Re(s)>0 If we look at Euler identity ##e^{ix}=\cos x+i\sin x##, how to get difference converge intervals...
  45. C

    Log transform on cylindrical coordinates

    Homework Statement I'd like to do a log transform on the radius variable of the heat conservation equation: qr - qr + Δr= ΔE/Δt where qr= -kA(dT/dr) My solution for this equation in cylindrical coordinates is: Tt+Δt=Tt+(Δt*k)/(ρ*c*Δr^2)* [(Tt-1-Tt)/(ln(rt/rt-1) - (Tt-Tt+1)/(ln(rt+1/rt)]...
  46. matqkks

    Transform Vector: Real Life Examples

    Why would we want to transform a vector in our normal basis (xyz axes) to another basis? The only situation I can recall is when we are looking at a force applied on an inclined plane. Are there any other real life examples where this may be necessary?
  47. B

    Laplace Sine Transform: Re[s]>0

    L[sin(at)]=\frac{a}{s^{2}+a^{2}}, Re[s]>0 L[e^{kt}]=\frac{1}{s-k}, s>k L[e^{-kt}]=\frac{1}{s+k}, s<-k L[sin(at)]=\frac{1}{2i}L[e^{iat}-e^{-iat}] =\frac{1}{2i}L[e^{iat}]-L[e^{-iat}] Using the above relations =\frac{1}{2i}[\frac{1}{s-ia}-\frac{1}{s+ia}], s>ia, s<-ia The problem is...
  48. E

    On the domain of the function that undergoes the Hilbert transform

    Hi all, This question is on the Hilbert transform, particularly on the domain of the input and output functions of the Hilbert transform. Before rising the question, consider the Fourier transform. The input is f(t) and the output is F(\omega). The function f and F are defined over...
  49. B

    Integration when transform to center of mass frame

    Hi, I am having some difficulty doing the integral ∫d^{3}v1d^{3}v2 | \overline{v1}-\overline{v2}|, where u1\leq|v1|,|v2|\lequ2, and \overline{v1} means vectors. It seems better to evaluate it in the center of mass frame, by substitution \overline{v1}+\overline{v2}=\overline{V}, and...
  50. 0

    Rectangular Fourier Transform and its Properties

    Is there a name for a transformation using the orthonormal base s_k(x)=\lceil \sin kx \rceil,\: c_k(x) = \lceil \cos kx \rceil \quad ? So basically a Fourier transform or Fourier series using periodic rectangles. What are the properties? Is there some kind of convolution theorem?
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