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
(
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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. F

    Must the Fourier transform exist for Dirac delta functions?

    I originally asked this in the Calculus & Analysis forum. But perhaps this is better suited as a question in Abstract algebra. For the set of all Dirac delta functions that have a difference for an argument, we have the property that: \int_{ - \infty }^\infty {{\rm{\delta (x -...
  2. W

    Is Oxygen Really Converted Into Energy in Our Bodies?

    I just started reading a pamphlet written my an M.D. about a poorly understood illness. On the second page he writes: "Hypoxia is a technical term meaning the inability to transform oxygen into energy." On the next page he writes: "It is due to a problem at the cellular level converting...
  3. A

    Changes in the internal structure during a Topological transform

    Changes in the internal structure during a "Topological transform" Is there any field of topology which deals with the changes in internal structure of an object when it undergoes topological transform? If I'm transforming a cube into a sphere, is there any 'field of topology' which analyze the...
  4. S

    Transform Maxwell Equations into k-space

    Dear fellow physicists, looking at the derivation for the maxwell equations into k-space, I've stumbled upon something that seems not so logical to me. It is concerning the two parts where they transform \nabla \times E and \nabla \bullet E on page 27 (on the sheets 14)...
  5. L

    Strong duality and coordniate transform

    Hello all, Assume we have an optimization problem and that strong duality holds. Will it also hold for another optimization problem obtained from the initial by a bijective coordinates transform? Thank you in advance.
  6. F

    Nonlinear differential equation (Laplace transform?)

    Hi, Part of my research, I nondimensionalized an ODE to eventually arrive at this form: sin(τλ) = q^((n+2)/(n+1)) + κq' + q'' where q' = dq/dτ The problem is of course the nonlinear q^n. n is an integer greater than 0. Is there a Laplace transform for this? Or what solutions are there for...
  7. C

    Fourier Transform of non-centered circular aperture

    Hi there, I have a little problem in wave optics: I have a wave function \psi_{ap} that depends on some geometric parameters, but that has no units itself (as one would expect). But unfortunately when I calculate the Fourier transform of this wave function the Fourier transform has a unit...
  8. C

    Transform a pde into rotating frame

    Hi, I have an equation of the form; \frac{d}{dt}(W) = \omega \left(x \frac{\partial}{\partial y} - y \frac{\partial}{\partial x} \right) W + g \frac{\partial}{\partial y} W + k x \frac{\partial^2}{\partial y^2} W I want to change it into the rotating frame using the transform; x...
  9. S

    Inverse Laplace transform with unit step function

    Hello again. First off, I wasn't sure how to say this in the title but I'm not taking the inverse Laplace transform of a unit step function. I'm taking the Laplace transform of something that comes out to the unit step function. I have this question, which is a similar version of the...
  10. Ookke

    Kinetic energy conservation in matter/energy transform

    ... C1.... C2-> P-> In the above illustration, P is a particle, C1 and C2 are detectors able to measure the energy/mass of a light pulse. C1 is at rest, P and C2 move horizontally to right with the same velocity. Let's say that P is actually a matter-antimatter pair that annihilates to...
  11. A

    Laplace transform uniqueness

    Consider one-sided Laplace transform:$$\mathcal{L} \left \{ h(t) \right \}=\int_{0^-}^{\infty}h(t)e^{-st}dt$$ Q. Is this defined only for the functions of the form f(t)u(t)? If no, then f(t)u(t) and f(t)u(t)+g(t)u(-t-1) are two different functions with the same Laplace transform, and thus...
  12. C

    Using a Fast Fourier Transform

    Hi I'm working on a project which takes up ECG signals and tries to evaluate the condition of the patient. For one particular disease (ventricular tachycardia) the ECG looks close to a sine wave. Hence, I find the predominant frequency in the signal. I shift the original signal now by half...
  13. N

    Solve Transformation Matrix of Object B in World Coordinates

    Homework Statement How to find the transformation matrix of Object B in world coordinates, when you know the transformation matrix of Object A in world coordinates and the matrix of Object B in Object A's local coordinates Please help!
  14. G

    Galilean transform and the maxwell equations

    So I keep hearing that the maxwell equations are variant under Galilean transform. Tired of simply accepting it without seeing the maths, I decided to do the transformation on my own. To make things easy, I only tried Gauss' law, furthermore I constricted the field to the x-axis only. So I have...
  15. ElijahRockers

    Laplace Transform of Step Function

    Homework Statement Solve y'' + y = f(t), y(0)=0, y'(0)=1, f(t)= (0 for 0<t<pi) (1 for pi<t<2pi) (0 for t>2pi) The Attempt at a Solution y'' + y = upi(t)-u2pi(t) s2L{y} -sy(0) -y'(0) +L{y} = L{upi(t)} -Lu2pi(t)} L{y}(s2+1) -1 = (e-pi*s/s) -(e-2pi*s/s) L{y} =...
  16. H

    The Correct Amplitude of a Fourier Transform

    If you take the absolute value of the FFT output, does that give you the amplitude? I am asking because I have seen example where that is taken as the amplitude, and examples were the absolute value is multiplied by either SQRT2 or by 2 to get the magnitude. So my question is what is...
  17. ElijahRockers

    Laplace transform of step function

    Homework Statement Find laplace trasform of g(t) g(t) = 0 for 0<t<1, t^2 for t>1 So this can be re-written as g(t) = t2*u1(t), where u is the unit step function. By using the fact that L(uc(t)f(t-c)) = e-csF(s) i am trying to take the laplace... So in this case, f(t-c) = t2 ... so then does...
  18. W

    Euler transform matrix multiplication help

    !Euler transform matrix multiplication help! Homework Statement This may be rather simple but i am really struggling to complete a 3 3x3 matrix multiplication. I NEED STEP BY STEP WORKING!. This would really help me I understand the theory. Basically I have three matrices T1= cosψ sin ψ...
  19. D

    Multi-Variable / Dimension Fourier Transform

    Multi-Variable / Dimension Fourier Decomposition Say we have f(x, y). We can Fourier decompose it in terms of f1(y, v) and e^{\ x\ v}, f2(x, u) and e^{\ u\ y}, or both variables simultaneously f3(u, v) and e^{\ x\ v\ +\ u\ y}. Similarly for any greater number of variables or dimensions. Now, is...
  20. Y

    Transform Word Doc to PDF and PDF to Word Doc.

    Hi I am looking for free software that can transform Word Doc to PDF. Maybe PDF back to Word Doc. Any suggestion on which one is good? Thanks Alan
  21. G

    Fourier transform capabilities in reconstructing missing data

    Hi, I know this topic is more suited for Computing & Technology, but it has even more to do with general questions about Fourier transform capabilities. I have a question about sample restoration in Discrete Fourier Transform. Suppose we have a signal with the stack of frequencies from 1 Hz...
  22. R

    Understanding Fourier Transform: Solving Homework with Clear Steps

    Homework Statement The Attempt at a Solution I don't understand this step. It's got to be some sort of identity that I missed. I also don't understand why the limits of integration change.
  23. B

    Fourier Transform help (bit )

    Fourier Transform help! (bit urgent) Hi there, I'm having a recurring problem with my Fourier transforms that I have tried really hard to figure out but I feel like I'm missing something important. It keeps popping up in my communications and signal processing papers. I keep getting FTs...
  24. S

    How to get time dilation & length contraction from Lorentz transform?

    OK, I've found a great explanation of the derivation of the Lorentz transformation, with x' = γ [ x - v t ] t' = γ [ t - ( v / c2 ) x ] so if I take the other term as 0, there is x'( t = 0 ) = γ x t'( x = 0 ) = γ t but the problem is that the time dilation & length...
  25. F

    When is the Fourier transform implied?

    I understand that if you have a system that is linear and time invariant, that you can perform a Fourier transform on it. But that doesn't mean you need to Fourier transform it. Or does it? Is a linear, time invariant system equivalent to or in some way implies a Fourier transform? Or is the...
  26. P

    Solve Laplace Transform: t{e^{ - t}}u(t - 1)

    Homework Statement Is there an easier way of solving this rather than doing the integral? Find the laplace transform of: t{e^{ - t}}u(t - 1) Homework Equations The Attempt at a Solution \int_1^\infty {t{e^{ - t}}} {e^{ - st}}dt = \int_1^\infty {t{e^{ - t(1 + s)}}} dt =...
  27. T

    Z-Transform, Cant find this transform

    Homework Statement I am attempting to perform a z-transformation on the terms 1/(z-3) and 1/(z-5) but I cannot find a sequence which fits this form in any of my tables. Is there a transform for these terms or do you just leave them as they are? Homework Equations The Attempt at a...
  28. C

    Question on rotational transform matrix, I

    Hi, I'm reading a book called Robotics, written by Tadej Bajd on my own to learn about robotics and have no one else to put my questions other than to the forums. Here the writer on 11th page writes: "By considering the similarity of triangles in Figure 2.3, it is not difficult to derive...
  29. C

    Laplace transform and fourier transform

    Homework Statement F{f(t)} is the Fourier transform of f(t) and L{f(t)} is the Laplace transform of f(t) why F{f(t)} = L{f(t)} where s = jw in L{f(t)} The Attempt at a Solution I suppose the definition of F{f(t)} is ∫[f(t)e^-jwt]dt where the lower integral limit is -∞...
  30. A

    Competing definitions of the Fourier transform

    Just began a serious study of the Fourier transform with a couple of books. One of them defines the Fourier transform on \mathbb R as \hat f(\xi) = \frac{1}{\sqrt{2\pi}} \int_{-\infty}^\infty f(x) e^{-i\xi x}dx. Another defines it as \hat f(\xi) = \int_{-\infty}^\infty f(x)...
  31. F

    Laplace transform with heavyside step function

    Homework Statement I need to solve the ODE y''-y = t - tH(t-1); y(0)=y'(0)=0 Homework Equations - The Attempt at a Solution I'm fine with the process of solving the ODE, but I need a little help regarding the first t. From what I understand from lectures, all of the 't' terms need to be in...
  32. M

    Very tricky Fourier transform

    I'm trying to evaluate the following intergral using complex function theory: \begin{equation} \int_{-\infty}^{\infty}\int_{-\infty}^{\infty}\frac{e^{i(ap+aq+b\sqrt{k^2-p^2-q^2})}}{\sqrt{k^2-p^2-q^2}}dpdq \end{equation}I though that it is possible if i can calculate: \begin{equation}...
  33. R

    Laplace transform and tabular integration

    Homework Statement The Attempt at a Solution I can't get the jump to [e^-st(-s cost bt + b sin bt)]/(s^2+b^2) They say they have to use integration by parts but when e and a trig ratio are involved that requires tabular integration. They're obviously not using tabular...
  34. R

    Understanding Laplace Transform: Step 1 to 2 Difficulty

    Homework Statement The Attempt at a Solution I can understand step 2 to 3, but I can't get step 1 to 2. For simplicity sake we'll just call e^(3-s)t = N since it will = N anyway ultimately. I think the answer should be [N/3-s - 1/(3-s)^2)N - (0 - 1/(3-s)^2)0 The second term...
  35. F

    I have to transform some machine for use them in United state

    Hi, First, I would like to ask for your apologize for my very bad english... My name is Frédéric Serrano, I'm a technician and I'm starting my own business. For a new contract my customer ask me to adapt his industrial machine for the USA. So I have to comeback to the basic rule. Here in...
  36. H

    Transform of a piecewise continuous function

    We know that the \mathcal L\{f(t)\} = \int^{\infty}_0 e^{-st}f(t) dt. Say we want to, for example, solve the following IVP: y'' + y = f(t) where f(t) = \begin{cases} 0 & 0 \leq t < \pi \\ 1 & \pi \leq t < 2\pi\\ 0 & 2\pi \leq t \end{cases} and y(0) = 0 , y'(0) = 0 We apply Laplace on both...
  37. G

    Lorentz transform of a scalar in QM

    If you Lorentz transform a scalar: U^{-1}(\Lambda)\phi(x)U(\Lambda)=\phi(\Lambda^{-1}x) If you now perform another Lorentz transform, would it it look like this: U^{-1}(\Lambda')U^{-1}(\Lambda)\phi(x)U(\Lambda)U(\Lambda')=\phi(\Lambda'^{-1}\Lambda^{-1}x) ? But isn't this wrong...
  38. O

    Fast Fourier Transform in Real Time

    I guess this is programming and physics all combined into one but hopefully I can get some help anyway. I am doing some signal analysis of real-time streaming sensor data. I would like to do a DFFT on the data in real time as it streams in. So far pretty easy, however, there are a number of...
  39. M

    Fourier Transform Tricky Integral

    Hi I am trying to analytically calculate the Fourier transform attached. I am getting really stuck with the integral, can anyone help? I've attached how far I've got with it, any help much appreciated! Kind Regards, Mike
  40. T

    I have 3 questions which are bessel, half range expression and laplace transform

    the questions are together with this file and my solutions are also attached. hope someone can comment on my solutions. thanks a lot and i hope i won't get any warning any more.
  41. H

    Why can't I substitute a Laplace transform into an integration?

    Hi, I was given the attached question and have given my wrong attempt at the answer. I know how to work the answer out (also shown) but I would like to know why my first attempt is wrong. Many Thanks
  42. H

    Laplace Transform: Solving Hi Everyone - Help Needed

    Hi everybody, can somewone tell me where am i wrong in this solution?(attached here) thank's
  43. E

    Fourier transform of a time integral

    Question: Derive the relationship \int^t_{- \infty} f(\tau) d \tau \Leftrightarrow \frac{F(\omega)}{j \omega} + \pi F(0) \delta (\omega) (where \Leftrightarrow means "Fourier transforms into"). Attempt: I have already proved the relationship \frac{dg(t)}{dt} \Leftrightarrow j \omega G(...
  44. T

    Definite integral evaluation (Inverse Fourier Sine Transform)

    Homework Statement I'm working on a long problem and have come to the final step. The answer seems so simple, but I can't quite get to it. I need to evaluate this integral: \int_0^{\infty}\ \left(e^{-k^2 t}/k\right)\sin(kx)\ dk Homework Equations Mathematica gives the result as...
  45. H

    What is the Inverse Fourier Transform of cos(4ω)?

    Hi everyone, I'm trying to solve an exercise in which I need to find x(t) considering that X(ω) = cos(4ω). So, I need to find the Inverse Fourier Transform of cos(4ω), but I don't have the inverse Fourier transform table. So, I thought about applying the duality property. If x(t) <-->...
  46. P

    MHB Fourier Transform of f'(ax): Discrepancy in Results?

    What is the Fourier transform of $f'(ax)$, where a>0 is a constant? Firstly, I reasoned that (lets say $F[f]$ is the Fourier transform of f) $F[f('x)]=\frac{1}{a}F[f](\frac{k}{a})$ by scaling theorem, then using the derivative rule we get $F[f'(ax)]=\frac{ik}{a}F[f(x)](\frac{k}{a})$. But when I...
  47. H

    Fourier Transform of Ohno Potential

    Ohno Potential is modeled by v(r)=\frac{U}{\alpha ^{2}r^{2}+1}. U and \alpha are constants. I try to Fourier transform it V(q)=\int V(r) e^{iqr\cos \theta}r^{2} \sin \theta d \phi d \theta dr It gives V(q) = 2 \pi U \int \frac {r \sin qr}{\sqrt{\alpha ^{2} r^{2}+1}} dr The...
  48. P

    Inverse fourier transform

    Homework Statement I can't figure out what the limits of integration should be; if a transfer function is given as follows: h(ω)=1 if 1<|ω|<2, 0 otherwise 1) find the impulse response 2) if the input is white noise of intensity σ² find the variance of the output signal 3)state...
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