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
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s
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=



0





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e


s
t



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

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  1. 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...
  2. 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 -...
  3. F

    MRI and Fourier transform to form an image

    I read about how MRI works briefly, by flipping the water molecules using a magnetic field to the correct state then send the radio wave to these atoms and have it bounces back to be received by receiver coils and apply Fourier Transform to figure out the imaging. My question is, how does...
  4. L

    Fourier transform of function which has only radial dependence

    3d Fourier transform of function which has only radial dependence ##f(r)##. Many authors in that case define \vec{k} \cdot \vec{r}=|\vec{k}||\vec{r}|\cos\theta where ##\theta## is angle in spherical polar coordinates. So \frac{1}{(2\pi)^3}\int\int_{V}\int e^{-i \vec{k} \cdot...
  5. H

    Can I use the Fourier Transform to analyze the Sun's Spectrum?

    I'm learning digital signal processing in my engineer class, but I'm more interested in apply these things into Astrophysics, so i know a little bit about for what is useful the Fourier Transform, so i thought why not use this in Analyzing the sun spectra! But what do you think!? Is it useful...
  6. 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?
  7. I

    Convolution (Possibly using Fourier transform)

    Homework Statement Find a function ##u## such that ##\int_{-\infty}^\infty u(x-y)e^{-|y|}dy=e^{-x^4}##. Homework Equations Not really sure how to approach this but here's a few of the formulas I tried to use. Fourier transform of convolution ##\mathscr{F} (f*g)(x) \to \hat f(\xi ) \hat g(\xi...
  8. R

    Fourier Transform: Nonperiodic vs Periodic Signals

    In a book the Fourier transform is defined like this. Let g(t) be a nonperiodic deterministic signal... and then the integrals are presented. So, I understand that the signal must be deterministic and not random. But why it has to be nonperiodic (aperiodic). The sin function is periodic and we...
  9. 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...
  10. LunaFly

    Why is Fourier Transform of a Real Function Complex?

    Homework Statement Find the Fourier transform F(w) of the function f(x) = [e-2x (x>0), 0 (x ≤ 0)]. Plot approximate curves using CAS by replacing infinite limit with finite limit. Homework Equations F(w) = 1/√(2π)*∫ f(x)*e-iwxdx, with limits of integration (-∞,∞). The Attempt at a Solution I...
  11. I

    Calculate indefinite integral using Fourier transform

    Homework Statement Use the Fourier transform to compute \int_{-\infty}^\infty \frac{(x^2+2)^2}{(x^4+4)^2}dx Homework Equations The Plancherel Theorem ##||f||^2=\frac{1}{2\pi}||\hat f ||^2## for all ##f \in L^2##. We also have a table with the Fourier transform of some function, the ones of...
  12. I

    Plancherel Theorem (Fourier transform)

    I'm having a hard time understand this theorem in our book: The Plancherel Theorem The Fourier transform, defined originally on ##L^1\cap L^2## extends uniquely to a map from ##L^2## from ##L^2## to itself that satisfies ##\langle \hat f, \hat g \rangle = 2\pi \langle f,g\rangle## and ##||\hat...
  13. B

    Optical Fourier Transform for Propagation

    Homework Statement The complex amplitudes of a monochromatic wave of wavelength ##\lambda## in the z=0 and z=d planes are f(x,y) and g(x,y), redprctively. Assume ##d=10^4 \lambda##, use harmonic analysis to determine g(x,y) in the following cases: (a) f(x,y)=1 ... (d) ##f(x,y)=cos^2(\pi y / 2...
  14. E

    Fourier Transform and Convolution

    Considering two functions of ##t##, ##f\left(t\right) = e^{3t}## and ##g\left(t\right) = e^{7t}##, which are to be convolved analytically will result to ##f\left(t\right) \ast g\left(t\right) = \frac{1}{4}\left(e^{7t} - e^{3t}\right)##. According to a Convolution Theorem, the convolution of two...
  15. N

    Bounds of a Fourier Transform

    If I have a wave function given to me in momentum space, bounded by constants, and I have to find the wave function in position space, when taking the Fourier transform, what will be my bounds in position space?
  16. T

    Understanding derivation of delta-y transform

    Hi, I was just looking over my textbook, and it mentions a ## \Delta##-y and y-## \Delta## transformation that is helpful for dealing with circuits in these configurations. The equations can be found here...
  17. B

    Fourier Transform of a sin(2pi*x)

    I have been very briefly introduced to Fourier transformations but the topic was not explained especially well (or I just didn't understand it!) We were shown the graphs with equations below and then their Fourier transformation (RHS). I understand the one for cos(2pist) but NOT the sin(2pist)...
  18. K

    Different forms of the discrete Fourier Transform

    Hi I am trying to program excel to take the DFT of a signal, then bring it back to the time domain after a low pass filter. I have a code that can handle simple data for example t = [ 0, 1, 2, 3] y = [2, 3, -1, 4] So I think everything is great and so I plug in my real signal and things go off...
  19. Estanho

    Transform that maps points from any quad to an reactangle

    Hello, This question might seem silly, but I've tried some approaches and none of them seemed to work. Here's my problem: I need some sort of transform that maps points from any quad to an rectangle. I will be using this on a computer graphics software, so you can think of this rectangle as my...
  20. S

    Definition clarification for Fourier transform

    I have been studying Fourier transforms lately. Specifically, I have been studying the form of the formula that uses the square root of 2π in the definition. Now here is the problem: In some sources, I see the forward and inverse transforms defined as such: F(k) = [1/(√2π)] ∫∞-∞ f(x)eikx dx...
  21. B

    Can you use the Lorentz transform for a function of time?

    Reading Griffiths, he states that the Lorentz Transform is useful for describing where an 'event' occurs in a different inertial frame. What about describing the motion of a particle in this moving frame if I know its motion in my frame? Really, I'm looking at pickup ions in the solar wind. A...
  22. S

    One question on the sampling theorem in Fourier transform

    Hello everyone, The question that I have may not be fully relevant to the title, but I thought that could be the best point to start the main question! I'm working on 2-D data which are images. For some reason, I have converted my data to a 1-D vector, and then transformed them to the...
  23. davidbenari

    How coordinate lines transform under ##e^z=\frac{a-w}{a+w}##

    Homework Statement Say how coordinate lines of the z plane transform when applied the following transformation ##e^z=\frac{a-w}{a+w}## Homework EquationsThe Attempt at a Solution This is exactly the way the problem is stated. It is a pretty weird transformation in my opinion and I'm guessing...
  24. 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...
  25. 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...
  26. Terocamo

    Fourier Transform of Dirac Comb/Impulse Train

    With Dirac Comb is defined as follow: $$III(t)=\sum_{n=-\infty}^\infty\delta(t-nT)$$ Fourier Transform from t domain to frequency domain can be obtained by: $$F(f)=\int_{-\infty}^{\infty}f(t)\cdot e^{-i2\pi ft}dt$$ I wonder why directly apply the above equation does not work for the Dirac Comb...
  27. rtransformation

    What does this two momentum transform look like?

    qi is the cartesian coordinate, and Qi is the Generalized coordinate, why the momentum under the two coordinates have this transformation way: pi=∑Pj(∂Qj/∂qj) pi and Pi are corresponding momentum under the two coordinate respectively.
  28. S

    Convolution and space-time Fourier transform

    Hi, I have a general function u(x,y,z,t). Then, (1) what would be the space-time Fourier transform of G⊗(∂nu/∂tn) and (2) would the relation G⊗(∂nu/∂tn) = ∂n(G⊗u)/∂tn hold true? Here, note that the symbol ⊗ represents convolution and G is a function of (x,y,z) only (i.e. it does not depend on...
  29. 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...
  30. T

    What method does a receiver or transmitter use to approx....

    Hi, I'm just curious because I know wifi uses digital FFT to send and receive signals. (I can't really remember why) But when I imagine a signal being sent its like a squiggily wave, so what method does the reciever use to approximate the instantanious values of the signal into a mathematical...
  31. S

    Why does large space correspond to low wavenumber in Fourier Transform?

    Hi In making Fourier Transform of a function, why is it said that large space (r) corresponds to low wavenumber(k)?
  32. 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...
  33. E

    Step Validity with the Fourier Transform of Convolution

    A convolution can be expressed in terms of Fourier Transform as thus, ##\mathcal{F}\left\{f \ast g\right\} = \mathcal{F}\left\{f\right\} \cdot \mathcal{F}\left\{g\right\}##. Considering this equation: ##g\left(x, y\right) = h\left(x, y\right) \ast f\left(x, y\right)## Are these steps valid...
  34. D

    Force Transform Applying: Question on a Specific Case

    When I try to apply the force transformation (the 3 vector one) to the describe following situation, I find a result that I can't make sense of. Hopefully someone can tell me what I'm doing wrong. Suppose observers A and B are in inertial frames, and B travels in the +x direction relative to A...
  35. P

    Books on the Fourier Transform

    I need a good book on the Fourier transform, which I know almost noting about. Some online sources were suggesting Bracewell's "The Fourier Transform & Its Applications." I gave it shot, but it's competely unreadable. On page 1 he throws out an internal expression and says "There, that's the...
  36. E

    Spatial Frequencies of the Fourier Transform

    The Fourier Transform transforms a function of space into a function of frequency. Considering a function ##f\left(x, y\right)##, the Fourier Transform of such a function is ##\mathcal{F}\left\{f\left(x, y\right)\right\} = F\left(p, q\right)##, where ##p## and ##q## are the spatial frequencies...
  37. T

    Transform from Magnitude of P to R

    Hi everyone! How do I transform Momentum to Position in spherical coordinates?Thinker301
  38. T

    Fourier Series: Understanding Non-Periodic Signals

    It's been quite a few years but I recently watched a video about how every picture can be represented by a number of overlapping constructive and destructive peaks from a Fourier (transform or series? I don't remember which). I remember that Fourier series was for periodic and transform was for...
  39. C

    What is the Stirling transform of (k-1)?

    While reading about combinatorial mathematics, I came across the Stirling transform. https://en.wikipedia.org/wiki/Stirling_transform So then, if I want to find the Stirling transform of, for instance, ##(k-1)!##, I have to compute this (using the explicit formula of the Stirling number of the...
  40. M

    MHB A question about FFT transform

    Suppose that there is a linear relation between discrete time (n) and frequency (f), then what is the relatian between x(n) and X(f) (X(f) is DFT transform of x(n))?
  41. G

    Fortran [Fortran] Filon's method Fourier Transform

    I was told to do a Fourier transform of function by using a Filon's method. I have found the code but I don't know how to include any function to the subroutine. I would be grateful for any example of how to use this code. SUBROUTINE FILONC ( DT, DOM, NMAX, C, CHAT ) C...
  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. P

    Problem with Fourier bessel transform of Yukawa potential

    Hello, I am trying to find Fourier Bessel Transform (i.e. Hankel transform of order zero) for Yukuwa potential of the form f(r) = - e1*e2*exp(-kappa*r)/(r) (e1, e2 and kappa are constants). I am using the discrete sine transform routine from FFTW ( with dst routine). For this potential...
  44. R

    What Fourier transform be called? Correlation or convolution?

    We know that in the Fourier transform formula ,there are mainly two terms function f(t) and complex exponential term ( function). But I am confused that what should i call Fourier transform formula as a correlation or convolution formula? So can anybody help regarding it?
  45. D

    Discrete Fourier Transform of Sine Function

    (1) For a real function, g(x), the Fourier integral transform is defined by g(x) = \int_{0}^{\infty} A(\omega )cos(2\pi \omega x)d\omega - \int_{0}^{\infty} B(\omega )sin(2\pi \omega x)d\omega where A(\omega ) = 2 \int_{-\infty}^{\infty} g(x)cos(2\pi \omega x)dx and B(\omega ) = 2...
  46. L

    Derive parameters from transform matrix

    Hello everybody, Sorry to ask you something that may be easy for you but I'm stuck. For example I have 2 images (size 2056x2056). One image of reference and the other is the same rotated from -90degrees. Using a program with keypoints, it gives me a transform matrix : a=2.056884522e+03...
  47. R

    How are Fourier Series and Fourier transform are related?

    We know that Fourier series is used for periodic sinusoidal signals and Fourier transform is used for aperiodic sinusoidal signals. But i want to know that Is there any relation present between Fourier Series and Fourier transform ? Also,Can we derive mathematical formula of Fourier...
  48. E

    Angular Spectrum Method and Fourier Transform

    Are the results of the Angular Spectrum Method and the Fourier Transform of a Fresnel Diffraction be different, or the same? Given the same distance between the input and output plane, and the same aperture.
  49. N

    What is the Correct Z-Transform of x(n) = -2^n u(-n-1)?

    Hi guys, I am trying to find the z-tranform of the following equation: x(n) =-2n u(-n-1) Using the Z-transform definition,summation and geometric series I am getting 1/(1-2z-1) But according to my lecturer the answer is suppose to be 0.5/(1-2z-1) I have tried simplification/factorization and...
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