What is Laplace transforms: Definition and 186 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. K

    Differential equation using laplace transforms

    Homework Statement y'' + y = delta(t-2*pi) The Attempt at a Solution I have solved this using laplace transforms. Y = e^(-2*pi*s)/(s^2 + 1) + 10s/(s^2 + 1) so that y = sint*u(t - 2*pi) + 10 *cost what I don't understand is this function is not definied for t<0. According to...
  2. B

    Laplace transforms; Abel's integral equation

    Using Laplace transforms, find the solution of Abel's integral equation: \int^{x}_{0}\frac{f(u)}{\sqrt{x-u}}du = 1 + x + x^2 I recognized that the integral is a Laplace convolution, leading to: (f*g)(x) = 1+x+x^2 where g(x)=x^{-1/2} So: L(f*g)=L(1)+L(x)+L(x^2)...
  3. L

    Understanding Laplace Transforms: Solving Problems and Applying Properties

    Hi all, 2 questions here 1) I've been doing some questions on laplace transforms and have been running into some trouble getting my answers into the same form as the answers given with the questions. For example: f(t) = 1 - e^(-t) Using the linearity property i got 1/s - 1/(s-1) which is...
  4. M

    Solving linear eqns using laplace transforms

    Hey can anyone tell me the method to solve this, I can do inverse linear eqns and such but i don't know how to solve this type of question: Use Laplace transforms to solve the following systems of linear equations (a)dx/dt= 3x(t) − 4y(t), dy/dt= 2x(t) + 3y(t), with initial conditions...
  5. M

    Book on laplace transforms & fourier series

    Hi hows it going, Im currently doing a linear maths course, i suppose it'd be introductory. I am using Elementary Linear algebra by Howard anton and find that very good. However the course goes on to deal with laplace transforms and Fourier series, can anyone recommend a good (introductory)...
  6. C

    Solve by means of Laplace transforms

    1. Please see attachment for Question I've put it into microsoft eqn editor. 2. I have not got a clue where to begin i don't want anyone to do it for me but some information on how i can do it for myself would be appreciated. 3. as above
  7. P

    Solving U_{tt}=9U_{xx} with Laplace Transforms

    We are supposed to work this using Laplace transforms U_{tt}=9U_{xx}; -infty<x<infty U(x,0)=sinx U_t(x,0)=0 The attempt at a solution Let L[U]=\hat{U} L[U_{tt}]=s^2\hat{U}-s(sinx) L[9U_{xx}]=9\hat{U}_{xx} s^2\hat{U}-s(sinx)=9\hat{U}_{xx}...
  8. A

    Laplace Transforms to solve non IVPs?

    Is it possible to use a laplace transform to solve a problem like x' + x = T where x is a function of T and x(0) = 5 and x(4) = 7 Or can you only solve initial value problems?
  9. C

    Using Laplace Transforms to Solve PDE

    Use the Laplace transform to solve \frac{\partial^2 y }{ \partial t^2 } = c^2 \frac{ \partial^2 y }{ \partial x^2 } for x>0, t>0 y(0,t) = t, for t>0 y(x,0) = 0, \frac{\partial y(x,0) }{ \partial t } = A, for x>0So I used the Laplace transform of a derivative, along with the initial conditions...
  10. E

    Solving Transcendental Equations (and Laplace Transforms)

    Homework Statement Given the equation H'(t) + u H(t - T) = 0 u > 0 Look for solutions of the form e^{rt} Show that these solutions are exponentially damped if e^{-1} > uT > 0 Find uT for which these solutions for r complex are oscillatory with growing, decaying, or constant amplitude. The...
  11. Saladsamurai

    Efficient Solution for System of Laplace Transforms with Initial Values

    Homework Statement Solve using Laplace Transforms \frac{dx}{dt}=x-2y \frac{dy}{dt}=5x-y Subject to x(0)=0 y(0)=0Okay. So I know that there are more efficient ways to solve this, but I missed the class in systems of Laplace Transforms and would like to get this resolved. I guess my...
  12. P

    Finding Inverse Laplace Transforms with Residue Method

    Homework Statement Inverse laplace transforms F(s)=\frac{5s-2}{s^{2}(s-1)(s+2)} Homework Equations Residue technique The Attempt at a Solution F(s)=\frac{5s-2}{s^{2}(s-1)(s+2)} = \frac{k1}{s^{2}} + \frac{k2}{s-1} + \frac{k3}{s+2} I solved for K1,K2, and K3, which all came to...
  13. S

    Differential equations - inverse laplace transforms

    Homework Statement We are given the following LaPlace Transformations and we are to find g(t) and h(t). L(g)(t) = 1/[(1-e^(-2s))(s-1)] L(h)(t) = (e^-s)/s(1-e^-s) Homework Equations By looking at the Table of LaPlace Transformations, the only one I found that could possibly work...
  14. D

    How Do You Derive Laplace Transforms for Delayed Functions?

    Homework Statement Derive the Laplace transform of the following functions, using first principles 3d) u(t - T) \} = 0, \ t<T \ (= 1, t>T) 3e) f(t) = e^{-a(t-T)}u(t-T) Homework Equations see above The Attempt at a Solution I know I need to derive the transform using by integration...
  15. P

    Engineering Solve RC Circuit Using Laplace Transforms

    Find v(t) at t=800ms for the circuit in Figure 1. Ans: 802mV Writing a single node equation we have \frac{v(t)-2tu(t)}{5}+0.1\frac{dv}{dt}=0. Taking the Laplace transform we have L\left\{ \frac{v(t)-2tu(t)}{5}+0.1\frac{dv}{dt}=0\right\} . tu(t)\Rightarrow\frac{1}{s^{2}}...
  16. G

    Laplace Transforms of Discontinuous functions

    Homework Statement (t − 1)^2u(t − 1) Find the Laplace transform. Homework Equations L{f(t-a)u(t-a)}(s) = e^-as F(s) The Attempt at a Solution The solution manual says take f(t) = t^2, I don't see why? Why is f(t) not (t-1)^2?
  17. M

    Laplace Transform of e^(-t)cos2t u(t-1)

    Homework Statement What is the laplace transform of e^(-t) cos 2t u(t-1) Homework Equations definition of Laplace transform: LT of f(t) = integral of f(t)e^-st dt, where limits of integration are from 0 to infinity The Attempt at a Solution since I have u(t-1) then do I just...
  18. B

    Derive 6 Help with Laplace Transforms

    I am new to Derive 6 and Laplace Transforms. Is it possible to solve the closed loop gain A/B of the attached loop using Derive 6. If it is possible, can someone guide me through the steps using Derive, as the problems that lie ahead will be much more complex, and I want to use Derive in the...
  19. V

    Laplace Transforms on PDEs: Non-dimensionalization

    Laplace Transforms on Partial Differential Equations - Non-dimensionalization too! Homework Statement The experiment described in the previous problem was analyzed from the point of view of long time \left(\frac{D_{AB}\,t}{L^2}\;>>\;1\right). We wish to reconsider this analysis in order to...
  20. E

    Help Needed with Laplace Transforms: Solve Before Tomorrow!

    I'm posting these as images because it would be difficult to type. If this isn't allowed, please let me know. I really need help with this before tomorrow, when I have a test. Any help appreciated. Homework Statement problem here The Attempt at a Solution I completed part 1 (solution here)...
  21. E

    Indefinite Integrals / Laplace Transforms

    Homework Statement Using improper integrals, find the Laplace transform of f(t)=t, determining the values of s for which the transform is valid.Homework Equations The Laplace transform F(s) of a function f is defined as ∞ / F(s)= | f(t)e^(-st) dt...
  22. C

    Laplace Transform of sin(3t)cos(3t) on t>=0 | Convolution Method

    Homework Statement Use a table to fing L{f(t)} for the given function f(t) defined on the interval t>=0 Homework Equations f(t)=sin(3t)cos(3t) The Attempt at a Solution Well this type of Laplace transform has got me stumped, I'm not to sure how to proceed. It doesn't seem to...
  23. C

    Solving Laplace Transforms - Hello from Dennis!

    well, I found this place searching for a method to solve a laplace transform as I'm a little stuck on exactly how to do it, So I'd like to say hello, and I hope I can be of some help for someone else in the future. also, do posts here go into a moderator queue before appearing , some other...
  24. U

    Using Laplace transforms to solve mass-spring-damper systems

    Hello everyone, I am actually a mechanical engineering major at the University of Texas, but I thought I'd ask you kind folks for help with this problem. I apologize in advance for this being difficult to read because I don't know how to type many of these symbols. Homework Statement...
  25. Y

    What is the Laplace inverse of F(s) = [3*e^(-4s)] / [s*(s^2 + s + 5/4)]?

    Homework Statement just a small part of a large problem ><a I am not even sure if this is in the right place. the first two questions i have to ask are really minor so i didnt want to make separate threads for each one. the third one is an actual problem itself tho. (1) i need the laplace...
  26. H

    Solving Laplace Transforms: y""-4y"'+6y" -4y'+y=0

    Can someone show me how to do these laplace transforms of these differentials? 1) y""-4y"'+6y" -4y'+y=0 y(0)=0, y'(0)=1, y"(0)=0, y"'(0)=1 2) y"-2y'+4y=0 y(0)=2, y'(0)=0 3) y"'+2y'+y=4e^-t y(0)=2, y'(0)=-1 4) y"-2y'+2y=cos(t) y(0)=1, y'(0)=0 the Laplace transfrom that i got for...
  27. J

    Studying for the FE test, never learned LaPlace Transforms.

    I began studying with a friend of mine for the FE (fundamentals of engineering) test and we began with the math section. We came across a LaPlace transform problem and we had never learned it before. Is this something I can learn relatively quickly (within the week)? I have taken calculus 1 2...
  28. M

    Laplace transforms and partial fractions

    Hey guys, I am supposed to find the Laplace transform of a set of ODEs. Ive broken it down a bit and I am left with finding the Laplace transform of: (-2e^-s)/(s(s+4)(s+1)) Is this something I have to use partial fractions for? Or is there another way? I am a bit confused.
  29. T

    Help with Laplace Transforms of Autonomous & Delayed Functions

    Could you please help me to do Laplace transformation ? That is an autonomous and nonlinear function on the right-hand side L{dx/dt}=L{1/1+x^a} where a is an integer other kind is in the form of delay L{dx/dt}=L{sin(x(t-\tau))} where \tau is delay, and real number
  30. D

    Laplace Transform of f(s) | Calculation of 𝜓(s)

    [tex] 1) \hat f(s) = 7/(s+2)(s^2+8s=41) \exp3s
  31. D

    Laplace Transforms and its applications

    Hi, I am taking a circuits analysis course currently. We are studying Laplace Transforms. I was wondering if anybody out there knows a way of bypassing all of the cumbersome complex algebra to find the partial fraction decomposition of a given function with respect to s. If not maybe...
  32. M

    Calculating Laplace Transform of g(t)=x(2t-5)u(2t-5)

    Ok, this is the question: Assume that the Laplace transform of x(t) is given as X(s)=s / (2s^(2) + 1). Determine the Laplace transform of the following function. g(t)=x(2t-5)u(2t-5) How do I use the transform they have given me to solve this...I guess my major problem lies using time...
  33. S

    Unit Step Function and Laplace Transforms

    Hey I was wondering if someone would check my work on this problem: Note: {\cal L} = Laplace {\cal U} = Unit Step Function {\cal L} \{ \cos(2t) \,\,\, {\cal U} (t - \pi)\} =e^{-\pi s} {\cal L} \{ \cos(2(t + \pi)) \} =e^{-\pi s} {\cal L} \{ \cos(2t + 2\pi) \} =e^{-\pi s}...
  34. B

    Laplace Transforms and non ideal inductors

    Hi there, I'm trying to derive an expression for the transient response (for a step input of magnitude V), for a non-ideal inductor modeled in the schematic I have drawn. This non-ideal inductor includes its inductance ( :smile: ), a parasitic parallel resistance and a parasitic capacitance...
  35. S

    What is the Laplace Transform of a Gaussian Distribution?

    I need a large table of Laplace transforms, do you know any good ones? Format HTML, Pdf, Ps, Latex or Word (?) Extra question: what is the Laplace transform of a Gaussian (normal distribution), with mean m and standard deviation s (assume equal to zero for t<0)?
  36. E

    Laplace transforms and the shifting theorem

    Can anyone explain to me the point of Laplace transforms and the shifting theorem in general?
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