David Goodmanson

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David Goodmanson

879 total contributions since 2012

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Answered
Modifying 'Bessel second-order ordinary differential equation' in matlab library.
Hi K^2, Take a look at J0(kr) and do the differentiations on d2/dr2 J0(kr) + (1/r) d/dr(J0(kr). Take out a factor of k for ea...

14 minutes ago | 0

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solving a system of 2nd order 2 ODE: output vector length not matching the initial condition vector length
Hi yosri, the reason this is happening is that the expression for dy/dt has four elements, but one of them contains diff(y(4)) ...

3 days ago | 0

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Create a vector field
Hi ALvaro, The code below sets P=Q=0 to make the spacial dependence more clear. Rather than meshgridding the 1d velocity vecto...

3 days ago | 0

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how can i calculate z^2 distibution?
Hello JS By gaussian I assume you mean the normal distribution, mean 0, std deviation 'a' f(z) = N*exp(-(z/a)^2/2) with N =...

4 days ago | 0

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Solve function returns expression in terms of z
Hello Ashmika, You do have a symbolic solution for h, which goes to show that symbolic solutions are not always the ideal. The...

4 days ago | 0

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How can I get randperm to return a permutation of a vector that has no entries at their original positions?
Hi Darcy, the methods I have seen here seem to involve trying randperm and rejecting the result if an element remains in the sa...

5 days ago | 0

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Imaginary numbers when solving ode (ode15s)
Hello YF, whenever unexpected complex quantities start appearing, it's time to look for the usual suspects, which tend to be ei...

7 days ago | 0

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Q Factor is not same
Hello Abdullah be aware that what you are calling alpha is often called alpha/2, but I don't think that had anything to do with...

8 days ago | 1

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How does nanstd function process complex numbers
Hi Luciano I'm not sure what you are referrng to with " nanstd(C) returns a complex matrix with dimentions equal to C and rea...

9 days ago | 0

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Power calculation from Voltage and current waveforms
Hi Stefano, The biggest issue is that when using trapz, you have not taken into account the width of the time steps when doing ...

9 days ago | 0

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FFT and Parseval's Theorem
Hi Chen, Here are a couple of ways. Since the time function fills up the entire time window (as opposed to being some kind of ...

11 days ago | 1

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In the sine wave source is the formula that links samples per period and sample time correct? It says: Samples per period = 2*pi / (Frequency * Sample time), but I believe it should be Samples per period = Sample time / Frequency.
Hello Ilaria, I believe it is neither of those. Rather it is what is in the PNG with the 2pi crossed out: samples/period = 1/...

14 days ago | 0

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Need help with this integral ? what is opstruct in integralcalc?
Hello HA I assume N is defined further on up since Matlab was not complaining about that. Try fun_2=@(t)(ones(size(t))*N); a...

14 days ago | 0

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How to obtain the coordinate of the maximum value in the Cross ambiguity function
Hi John, Not having the phased array system toolbox I don't know how the plot axes are oriented, but I think one of the two pos...

14 days ago | 0

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solving ode equation using ode45
Hi nadeeshani, UPDATED ANSWER This is a speculative answer, but perhaps you did not take the square root when you calculated t...

15 days ago | 0

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Why am I only getting partial streamlines.
Hi Boris, the problem is the line sy = sx./sx which creates a vector of ones for sy. Then every streamline originates at the h...

17 days ago | 0

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Non-Integer For-Loop
Hi Christopher for h = 0:.1:1 works, although with the interval expressed in floating point, you have to be careful. for ...

17 days ago | 1

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Why is dsolve solution halved from real answer?
Hi Miles, One of your conditions is dy/dt = 0 which is iffy, since there is a dirac delta function at the origin and you are no...

19 days ago | 4

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error in computing atanh
Hello Francisco, The imaginary part is i*pi/2, so the two answers are a+i*pi/2 and a-i*pi/2, where a is real. Both answers are...

21 days ago | 1

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Significance of Nyquist frequency and Maximum frequency THD computation for FFT analysis
Hi Alsher, you don't show the horizontal frequency scale but I believe that the very small peaks have spacing 5 Hz, there are 1...

25 days ago | 0

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How to calculate error of trapz() function?
Hi Emil, Although there are uncertainties, you can draw some conclusions by using reasonable assumptions. First, you have to b...

27 days ago | 0

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How do I prevent overwriting of matrix elements?
Hi Domantas This is just a provisional answer since I am not sure exactly what you are trying to do, but statements like H(1:...

29 days ago | 0

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How do I use acot(x) as a continuous function in matlab?
Hi Michael, I believe that 1/2 - (1/pi)*atan(x) fills the bill. It's the same as (1/pi)*acot(x) for x>0 and is continuous, w...

30 days ago | 1

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Answered
3D Plot of particle trajectory in E and B field
Hi Lujain, After setting v = [0 1 1] to provide some initial z velocity, figure(2) plot3(X(:,1),X(:,2),X(:,3)) grid on and ...

1 month ago | 0

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How to Find the Rotation Matrix?
Hi ercan, MODIFIED First of all, for a rotation matrix the two known columns have to be an orthonormal pair, meaning that ther...

1 month ago | 2

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Waveform not staring at origin
Hi SA, If you temporarily set c0 = 0 you obtain a nice trapezoidal wave of amplitude 1 that oscillates about y = 0 and has a me...

1 month ago | 0

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How do I find a D matrix that satisfies [K]*inv(M)*[D]==[D]*inv(M)*[K] ?
Hi Ikram, Using N in place of inv(M) for simplicity, you are looking for a D such that K*N*D = D*N*K Let K*N and N*K have eig...

1 month ago | 0

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Answered
Is there anyway to calculate the position in coordinates of points using a n*n distance matrix?
Hi Meme, first of all, if all you have are the distances between points, you can translate the all the points together in the 2...

1 month ago | 0

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Summation subroutine giving result as NaN (not a number)!
Hi Louis, the basic problem is that in the product calculation you have for l=0:n if (l~=j) && (l~=i) && (l~=m) prod=p...

2 months ago | 0

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Answered
Replace diagonals in a matrix
Hi Hasan, here is one way r = rand(7,7) n = size(r,1); m = (n-1)/2; a = (-m:m)-(-m:m)'; r(abs(a)>1)=0 assuming the main...

2 months ago | 0