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David Goodmanson


David Goodmanson

566 total contributions since 2012

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Answered
Question about fft2(2D Fourier Transform) of a Gaussian function
Hi Zhu Li, A couple of things are going on here. First, there is the checkerboard pattern in the angle plot. I added an extra ...

1 jour ago | 1

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Answered
The power sum of all frequencies seems that the half amount of the middle frequency power is not added. But the algorithm accords with the Parseval theorem. why?
Hi H^2, It helps that you are doing this for four frequencies rather than some crazy huge number of them. x = 1:4; N = length...

4 jours ago | 0

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Answered
Problem with symbolic Fourier Transform
Hello Halil, For the delta function, delta(x-x0) = |a| delta(a(x-x0)) so with a = 2*pi, both versions are correct. quick lo...

4 jours ago | 1

Answered
How does function std process complex numbers
Hi JFz, First of all, for a matrix the std is calculated independently for each column, as is true of many Matlab functions. F...

10 jours ago | 1

| accepted

Answered
Simple squaring of expression
HI Wesley, syms a syms b syms c syms d syms e f = expand((1*a+2*b+3*c+4*d+5*e-8)*(1*a+2*b+3*c+4*d+5*e-8))

11 jours ago | 0

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Answered
How to solve this equation which contains complex number, bessel equation and its derivative?
Hi bohan shen, The first six roots are shown below. First, since J1 is odd and J0,J2 are even, if z is a root then so is -z. ...

11 jours ago | 1

| accepted

Answered
How do I assign matrix of strings to matrix of numbers?
Hi [A,B,C,D,E,F] = deal(5,8,2,9,2,1) although for a large number of variables, giving each its own name is not a winning strate...

11 jours ago | 0

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Answered
Finding and plotting radial component in vector field
Hi djr, nc = 14; nr = 14; % Create grid [x,y] = meshgrid(0:dx:(nc-1)*dx,0:dy:(nr-1)*dy); % Plot vectors (rows and colomns ne...

13 jours ago | 0

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Answered
How to solve first-order nonlinear differential equation where the solution is coupled with an integral?
Hi Califfo; This may be in line with what you want. At least it's changing size It's based on the idea that you know not onl...

18 jours ago | 2

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Answered
Errors when solving equation numerically with a Heaviside Theta
Hi A7, The code below finds a solution. Instead of looking for phi0 directly it uses the variable beta = 1/(lambda*phi0) Sin...

19 jours ago | 0

Answered
Randomly select an element from a vector satisfying a condition
Relative speeds are going to depend on the length of X and the value N that the elements have to be greater than, (2 in the exam...

20 jours ago | 0

Answered
Matrix grouping result of combinations
Hello Joao, Maybe I need to write better blurbs. Here is a general solution for even n, with a verification check that shows t...

22 jours ago | 0

Answered
Mesh doesn't work for cone shape?
Hello TY, I don't know if you need a fancier triangular mesh, but here is a way to a 'square' one. r = 0:.05:1; th = linspace...

22 jours ago | 0

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Answered
Standard deviation of decimal numbers
Hi Jill, This is just the usual numerical 'error' due to the limitations of floating point arithmetic. std(.1*(ones(1,1e5)))...

26 jours ago | 1

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Answered
Create block sparse matrix
HI ks, Here is one way. MODIFIED (see comment thread below) showing two possible methods to fill the matrix by means of a ...

26 jours ago | 1

Answered
Flatten Matrix in Row Major Order in Arbitrary Dimensions
Hello Lucas-Raphael, I'm not sure this is what you are looking for, but B = permute(A,[6 5 4 3 2 1]); % (however many dim...

environ un mois ago | 0

Answered
Looking for a function f(x,y,z) based on 3 points to calculate interpolated/extrapolated values with a linear relation
HI Appli, This is something Matlab does really well. I assume by 'linear relation' you mean that each point has a value c = a...

environ un mois ago | 1

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Answered
Cannot plot Fourier Transform
Hi Reza, If you take a look at X, the result is X = -((pi*w*sign(w))/2 + fourier(cos(4*t)/t^2, t, w)/2)/pi^2 which shows tha...

environ un mois ago | 0

Answered
IFFT integration doesn't match cumtrapz integration
Hi NIk, This is an Interesting problem. Let g be the function and G its integral. If you just want to key in on an improved r...

environ un mois ago | 0

Answered
Obtain eigenvalue from matrix and known eigenvector
Hi Henry, you can find the indices where x = 0 and cast those entries out of both x and the corresponding rows and columns of A...

environ un mois ago | 0

Answered
fftshift with even and odd number of data points (scaling the positive and negative frequency axis)
Hi Farooq, [1] For N odd, the frequencies before and after using fftshift (or ifftshift) are as you say: N = 9 example: fo...

environ 2 mois ago | 1

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Answered
Getting a smooth curve instead of two linear functions
Hi Arber, This can be done reasonably well by a hyperola whose asymptotes are the two lines in question. The hyperbola of cour...

2 mois ago | 2

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Answered
eigs bug for 0 as lowest eigenvalue in parts of the matlab versions
Hi pl, 2018b does not list 'sa' as an option for eigs, so I am speculating that that 'sa' is legacy. However, compariing 'sa' t...

2 mois ago | 0

Answered
Reduce the computional time to calculate the mutilplying two matrixes
Hi Thu, try % N = 1000; % M = 200; Q00 = reshape(Q0,N,N*M); ff = reshape(w'*Q00,N,M)'; This is approximately four times f...

2 mois ago | 1

Answered
sine fit in matlab vs closed-form expressions (linear least squares)
Hi Thales, Before doing the least squares calculation it makes sense to try the less ambitious result of finding the right ampl...

2 mois ago | 2

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Answered
Replace vector of idexes with values from another vector corresponding to those indexes
Hi Nate, c = b(a) gets it done. a becomes an index vector into the elements of b.

2 mois ago | 1

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Answered
Division problems wiht matrix, calculation error
Hi Eduardo, It's quite likely that two of the displayed values for LineInf and LineSup are not what you think they are. The va...

2 mois ago | 0

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Answered
Audio fft shape is too strange.
Hi eunbae, The code is pretty close. The fft of a real signal has positive and negative frequencies, and what you are seeing a...

2 mois ago | 1

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Answered
Is It possible create a function that, given an equation, finds the value of the (x) so the two members are equal?
Hi Gianmarco, the two equations aren't coupled, and using fzero on Mp^2 seems to work. In the first equation I multiplied by b...

3 mois ago | 0

Answered
Defining derivatives in ode45
Hello sina, If you turn the diagram around by 180 degrees and then let Ca <--> Cb, you get exactly the same diagram that you st...

3 mois ago | 1

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