Laplace transform Definition and 779 Threads

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



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t
.


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

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  1. V

    Laplace transform to solve a nonhomogeneous equation

    Mod note: Moved from a Homework section can i use the Laplace transform to solve a nonhomogeneous equation if i have these Initial condition s(x) and s(-x)
  2. R

    Integrating Sums (Laplace Transform)

    Homework Statement Using: \mathcal{L}\big\{t^n\big\}=\frac{n!}{s^{n+1}}\text{for all s>0} Give a formula for the Laplace transform of an arbitrary nth degree polynomial p(t)=a_0+a_1t^1+a_2t^2+...+a_nt^n Homework Equations \mathcal{L}=\lim_{b\rightarrow\infty}\int_{0}^{b}p(t)e^{-st}dt The...
  3. J

    Low Pass Filters and Laplace Transform

    Homework Statement Given that r(t) = L^-1 (Inverse laplace) *H(S) and by making the link between the time-domain and frequency-domain responses of a network, explain in detail why the ideal “brick-wall” lowpass filter is not realisable in practice. [/B]Homework EquationsThe Attempt at...
  4. R

    How Do You Select Sigma for Different Regions in Inverse Laplace Transforms?

    Homework Statement Given the Laplace transform $$F_L(s) = \frac{1}{(s+2)(s^2+4)},$$ by using the complex inversion formula compute the inverse Laplace transform, ##f(t),## for the following regions of convergence: (i) ##Re(s)<-2;## (ii) ##-2<Re(s)<0;## (iii) ##Re(s)>0.## Homework Equations...
  5. MAGNIBORO

    I Does the Laplace Transform Exist for tanh(x)?

    hi, sorry for the bad english. exist a Laplace Transform of tanh(x)? i know math of high school, so sorry if it is a question a little silly thanks
  6. S

    MHB Laplace Transform Help: Solving for Unknown Variables in Electrical Circuits

    Evening All I have had a go at a laplace transform and got stuck. $$\frac{d^2v}{dt^2}+\frac R L \d v t+\frac 1{LC}v=\frac 1{LC}V_0$$ $$R=12 \Omega, L=0.16H, C=10^{-4}F, V_0=6V, v(0)=0, v'(0)=0$$ so subbing these in i get $$\mathscr L \left[ \frac {d^2v}{dt^2}+75\d v t+62500 v...
  7. D

    I Find Y(s)/X(s) for y(t) = u(t - a).x(t)

    y(t) = u(t - a) . x(t) u(t) is a unit step function. I have to find Y(s)/X(s). Do I have to do convolution in frequency domain?
  8. T

    How Do You Solve a First Order Laplace Transform with a Ramp Input?

    Homework Statement A process can be represented by the first order equation (4δy(t)/δt) + y(t) = 3u(t) Assume the initial state is steady (y = 0 at t = –0). (a) Determine the transfer function of this process in the s domain. (b) If the input is a ramp change in u(t) = 4t, determine the...
  9. P

    MHB Emad's question via email about Inverse Laplace Transform

    The closest Inverse Laplace Transform from my table is $\displaystyle \begin{align*} \mathcal{L}^{-1}\,\left\{ \frac{2\,a\,s\,\omega}{\left( s^2 + \omega ^2 - a^2 \right) ^2 + 4\,a^2\,\omega ^2 } \right\} = \sin{ \left( \omega \, t \right) } \sinh{ \left( a \, t \right) } \end{align*}$ so we...
  10. F

    Laplace transform of (2s^2 +10s) / ((s^2 -2s +5)(s+1))

    Homework Statement (2s^2) +10s / (s^2 -2s +5 )(s+1) , I have checked the partial fraction , it's correct , but according to the ans it's (e^t)[(3cos2t + 2.5sin2t)] - (e^-t), but my ans is (e^t)[(3cos2t + 4sin2t)] - (e^-t)Homework EquationsThe Attempt at a Solution
  11. ltkach2015

    Dartmouth Extended Laplace Tables -- Not general enough? item26.a

    Homework Statement [/B] http://www.dartmouth.edu/~sullivan/22files/New%20Laplace%20Transform%20Table.pdf (see item 26a) homogenous solution to underdamped in amplitude phase form: (see attached image) 2. Relevant info - non zero initial conditions: x(t=0) = xo AND dx/dt(t=0) = vo - unforced...
  12. J

    I Heaviside's Operational Calculus and Laplace Transform

    Hello everyone, I was studing Heaviside's operators for solving ODE, which I strongly recommend to have a look because it helps a lot when the differential equations have "exotic" inhomogeneous terms, but it is a method that works and you do not know exactly why. Some biographies tell that...
  13. D

    A question on Laplace transform

    x(t) and y(t) are related by y(t)=1/(x(t) -k), how should I derive Y(s)/X(s)?
  14. H

    Understanding the Laplace Transform for Right-Handed Notes

    for the right part of the notes, why the integral of (e^-su)f(u) from 0 to T will become integral of (e^-st)f(t) from 0 to T suddenly ? why not integral of (e^-s (t-nT) )f(t-nT) from 0 to T ? as we can see, u = t +nTd given/known dataHomework EquationsThe Attempt at a Solution
  15. J

    Laplace Transform unit step function

    Homework Statement g(t) = (t+1)us(t) - (t-1)us(t-1) - 2us(t-1) - (t - 2)us(t-2) + (t-3)us)(t - 3) + us(t-3) Homework Equations unit step function us(t-3) is same as u3 (t) Shift in time: L[f(t - T)us(t-T)] = e-TsF(s) us(t) ↔ 1/s t ⇔ 1/s2 The Attempt at a Solution 1/s2 + 1/s - e-s/s2 + e-s/s -...
  16. A

    How Do You Apply Laplace Transforms to Vehicle Suspension Analysis?

    Homework Statement Diagram for a vehicle suspension is given. Displacement of wheel is given by 'x' and and displacement of body is 'y'. Spring constant, k = (7*10^4) Nm Damping coefficient, c = (3*10^3) N/m/s mass,m = 250kg a) Make a Laplace Transform of system and utilize it to predict 'y'...
  17. j3dwards

    Explicit check for Laplace transform?

    Homework Statement Solve the following initial value problem using Laplace transforms: y' + 4y = 3t3 e−4t ; y(0) = 0 . Useful information: Recall that the Laplace transform of y 0 is pY − y(0), where Y is the Laplace Transform of y. The Laplace transform of tk e−at is k!/(p + a)k+1 . Confirm...
  18. R

    Solving ODE by Laplace Transform: Where Did I Go Wrong?

    Homework Statement Use Laplace transform to solve the following ODE Homework Equations xy'' + y' + 4xy = 0, y(0) = 3, y'(0) = 0 The Attempt at a Solution L(xy'') = -\frac{dL(y'')}{ds} L(4xy) = -\frac{4dL(y)}{ds} L(y'') = s²L(y) - sy(0) - y'(0) = s²L(y) -3s L(y') = sL(y) - sy(0) - y(0) =...
  19. L

    MHB Rieman inversion formula in Laplace transform

    Hello everybody! I'm sorry if it's not the right section to post in. I'm trying to solve this exercise: \frac{1}{2i\pi}*\int_{8-i\infty}^{8+i\infty}\frac{e^{s(t-5)}}{(s+4)^2}ds The request is to find the result in function of t I know i must use the Riemann inversion formula, and so the request...
  20. I

    MHB Laplace Transform: Basic Concepts & Applications

    Did I do this right? View image: 20151201 143310 1
  21. I

    MHB How do I find the Laplace Transform for U3(t)(t-3)^5/2?

    I'm working on a few problems to find Laplace transforms and I got stuck on this one. ${U}_{3}(t){(t-3)}^{5/2}$ It looks different from the other I've been doing so I don't really know how to get started
  22. Crush1986

    Can Laplace Transforms Reveal Bessel Functions as Solutions?

    Homework Statement xy''+y'+xy=0, y'(0)=0, y(0)=0 Using the method of Laplace transforms, show that the solution is the Bessel function of order zero. Homework Equations -(d/ds)L{f(x)} The Attempt at a Solution The only thing I got out of this when trying to solve it was y=0. Obviously not...
  23. Mark Brewer

    How can partial fractions be used to solve inverse Laplace transforms?

    Homework Statement L-1{(2s2+3)/(s2+3s-4)2} The Attempt at a Solution I factored the denominator f(t)=(2s2+3)/((s-1)(s+4))2 now I've tried partial fractions to get (2s2+3)/((s-1)(s+4))2 = A/(s-1)2 + B(s+4)2 (2s2+3)=A(s+4)2 + B(s-1)2 by substitution, s=1 and s=-4 5=A(25) A=1/5 35=B(25)...
  24. jdawg

    Understanding the Inverse Laplace Transform: Solving for 3/s√(π)

    Homework Statement L-1{3/s1/2} Homework EquationsThe Attempt at a Solution 3L-1{1/s1/2} 3L-1{(1/sqrt(π))(sqrt(π)/(sqrt(s))} 3/(sqrt(π))L-1{(sqrt(π))/(sqrt(s))} 3/(sqrt(π))(1/(sqrt(t)) This is what I got from the solution for this problem. What tipped them off to multiply by sqrt(π)? And...
  25. H

    How to solve this problem using laplace transform?

    Homework Statement The differential equation given: y''-y'-2y=4t2 Homework EquationsThe Attempt at a Solution I used the laplace transform table to construct this equation,and then I did partial fraction for finding the inverse laplace transform.But I'm now stuck at finding the inverse laplace...
  26. J

    How would I take the laplace transform of f(t)= te^tsin^2(t)?

    How would I take the laplace transform of f(t)= te^tsin^2(t)?
  27. D

    Laplace tranform of unitstep (heaviside) function

    Homework Statement [/B] I know for t[u(t)-u(t-2)], we can simplify that to tu(t)-((t-2)+2)u(t-2) which then gives us tu(t)-(t-2)u(t-2)-u(t-2). Now, the laplace transform seems trivial but I am having problems with this equation: sin(t)[u(t)-u(t-pi)] Homework...
  28. Linder88

    How Do You Apply Laplace Transform to an ODE with a Derivative of Time?

    The ordinary differential equation, with initial values,shall be solved using Laplace transform. The ODE looks like this \begin{equation} y''(t')+2y''(t)-2y(t)=0 \end{equation} And the initial conditions are \begin{equation} y(0)=y'(0)=0, y''(0)=0 \end{equation} The problem is with the first...
  29. Aristotle

    Laplace Transform Method for Solving Initial Value Problems

    Homework Statement Use laplace transforms to find following initial value problem -- there is no credit for partial fractions. (i assume my teacher is against using it..) y'' + 2y' + 2y = 2 ; y(0)= y'(0) = 0 Homework Equations Lf'' = ((s^2)*F) - s*f(0) - f'(0) Lf' = sF - f(0) Lf = F(s) The...
  30. Aristotle

    Initial Value Problem using Laplace Transform help?

    Homework Statement Use laplace transforms to find following initial value problem -- there is no credit for partial fractions. (i assume my teach is against using it..) y'' - 4y' + 3y = 0 ; y(0)=2 y'(0) = 8 Homework Equations Lf'' = ((s^2)*F) - s*f(0) - f'(0) Lf' = sF -...
  31. J

    Is there a mistake in my calculation or in my reasoning?

    Homework Statement y'' + 3y' + 2y = r(t), r(t) = u(t - 1) - u(t - 2), y(0) = y'(0) = 0. I need to solve this by convolution, which I know is commutative. The problem is that my calculation gives (f * g) =/= (g * f). Could someone please tell me where my mistake is? Homework Equations...
  32. O

    Quick laplace transform question

    Homework Statement So I know 1/(s-a)=e^(a1), but why is say, 2/((s+4)^2) equal to 2xe^-4x? Do I just simply add an X if the numeration is a constant other than 1?
  33. I

    Solving ODE with Laplace transform

    Homework Statement Let ##f(t)= \begin{cases} \sin t , \; \; 0 \le t < \pi \\ 0 , \; \; \; \; \; \text{else.} \end{cases}## Use Laplace transform to solve the initial value problem ##x'(t)+x(t)=f(t), \; \; \; x(0)=0.## Homework Equations Some useful Laplace transforms...
  34. J

    Keep getting the wrong answer in this lengthy Laplace problem

    Homework Statement y'' + 4y = 8t^2 if 0 < t < 5, and 0 if t > 5; y(1) = 1 + cos(2), y'(1) = 4 - 2sin(2). Use the Laplace transform to find y. Homework Equations t-shift, s-shift, unit step function. The Attempt at a Solution I have been trying to solve it for hours, but keep getting the wrong...
  35. C

    Laplace Transforms Involving: Unit-Step, and Ramp Functions

    Homework Statement Here is an imgur link to my assignment: http://imgur.com/N0l2Buk I also uploaded it as a picture and attached it to this post. Homework Equations u_c (t) = \begin{cases} 1 & \text{if } t \geq c \\ 0 & \text{if } t < c \end{cases} The Attempt at a Solution Question 1.1 -...
  36. Italo Campoli

    Inverse Laplace Transform of a fractional F(s)

    Homework Statement [/B] Having a little trouble solving this fractional inverse Laplace were the den. is a irreducible repeated factor 2. The attempt at a solution tryed at first with partial fractions but that didnt got me anywhere, i know i could use tables at the 2nd fraction i got as...
  37. Italo Campoli

    Prove a Laplace Transform Equality

    Homework Statement Prove that http://www4f.wolframalpha.com/Calculate/MSP/MSP26931c1531g07285beh7000062h7f6g1ggd95eea?MSPStoreType=image/gif&s=5&w=98.&h=38. =http://www4f.wolframalpha.com/Calculate/MSP/MSP6901c153574d0bdbh20000048829f0g4d1fi1d0?MSPStoreType=image/gif&s=5&w=69.&h=35. The...
  38. khurram usman

    A discussion about Fourier and Laplace transforms and calculus

    i have read many of the answers and explanations about the similarities and differences between laplace and Fourier transform. Laplace can be used to analyze unstable systems. Fourier is a subset of laplace. Some signals have Fourier but laplace is not defined , for instance cosine or sine...
  39. S

    Second shifting theorem of Laplace transform

    Can anybody direct me towards a proof of the second shifting theorem for Laplace transforms? I'm understanding how to use it but I can't figure out where it comes from. I've been learning from Boas, which doesn't offer much in way of proof for this theorem. Are there any good resources online...
  40. B

    How Do You Apply ζ in an Initial Value Problem When Using Laplace Transform?

    hi, if there is a initial value problem with a ζ in it with specified values what do you do with it when taking the laplace transform?
  41. Destroxia

    Step Function IVP Differential Equation w/ Laplace Transform

    Homework Statement (didn't know how to make piecewise function so I took screenshot) Homework EquationsThe Attempt at a Solution My issue here with this problem is that I have absolutely no idea where to start... I have read through the textbook numerous times, and searched all over the...
  42. H

    Need explanation on Laplace Transform and Fourier Transform

    Hello guys. I need an easy explanation regarding Laplace Transform and Fourier Transform. I know it is quite a mathematics question but I need an explanation in which it has something to do with engineering. I already search a bit about them but still cannot find and explanation that easy enough...
  43. A

    Laplace transform of anti causal systems

    The unilateral laplace transform integrates from 0 to infinity.Then how can i take laplace transform of exp(t)u(-t)?PS:I don't want to flip it and use time scaling property.
  44. S

    Inverse Discrete Laplace Transform

    Hi, I have an idea which when tested looks like its clearly flawed. I am hoping someone can tell me where my procedure is flawed, or point me to some other theory that has already done something similar. The first two are the laplace transform. The third line is the Fourier Transform. The...
  45. P

    MHB Johnsy's question over Facebook about an Inverse Laplace Transform

    To start with, apply partial fractions... $\displaystyle \begin{align*} \frac{A\,s + B}{ s^2 + 9} + \frac{C\,s + D}{ \left( s^2 + 9 \right) ^2 } &\equiv \frac{ 4s^3 + 5s^2 + 57s + 45}{ \left( s^2 + 9 \right) ^2 } \\ \left( A\,s + B \right) \left( s^2 + 9 \right) + C\,s + D &\equiv 4s^3 + 5s^2 +...
  46. J

    Laplace Transform question with unit step function

    Homework Statement Homework Equations Laplace Trasformations The Attempt at a Solution a. done b. f(t)= t -3*t*u(t-1) + 4*u(t-1) -3*u(t-2) -2*t*(t-2) c. 1/(s^2) - (3e^-s -2e^-2s)/(s^3) + (4e^-s -3e^-2s)/s d. 1/(s-1) * (1/(s^2) - (3e^-s -2e^-2s)/(s^3) + (4e^-s -3e^-2s)/s) These are the...
  47. Feodalherren

    What is the issue with applying the Laplace transform to tcos(4t)?

    Homework Statement f(t)=tcos(4t)Homework Equations tnf(t)=(-1)n dF(s)/dsn The Attempt at a Solution I don't understand why this formula is giving me the oppiste sign of the answer. If I apply the formula I get (16-s2)/(s2+16)2 Because n=1 I need to multiply by a negative but this yields...
  48. M

    Convolution theorem for Laplace Transform proof

    Hi all. Sorry about creating this new threat despite existing some others on the same topic. I have a problem in understanding a very specific step in the mentioned proof. Let me take the proof given in this link as our guide. My problem is just at the ending. When it says: "The region...
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