David Goodmanson

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David Goodmanson

806 total contributions since 2012

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Answered
Poisson Boltzmann eq. with an infinite boundary condition
Hi Roi For convenience I will use u in place of psi. An exact solution is tanh(u/4) = A*exp(-x) where A = tanh(1/4) ...

5 days ago | 1

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Can I use the PDEPE solver to solve the following dimensionless Transient PFR PDE? If not, what method do you reconmend?
Hello Rogelio, For psi(t,eta) I assume that the boundary conditions are psi(0,eta) = 0 for all eta an...

7 days ago | 0

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double peaks in FFT matlab
Hello hamzah the fft is a complex function. Are you plotting only the real part? This problem is occurring because your delta...

10 days ago | 0

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How to plot wavelength and wavenumber FFT from intensity data
Hi Arwi, n = 3648, dpix = 8e-9; % 8nm seems small for a pixel width The x array has spacing delx = dpix and is x = delx*(0:...

13 days ago | 0

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Verifying the uncertainty principle with fft for Gaussian
Hello Ori, The problem stems from the following, where I am using t and f rather than x and k (see comment). For an fft, once ...

14 days ago | 0

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why the Real and imaginary part of fourier transform (fft) are not zero for real odd function
Hi Jiali, with an even number of points the symmetry is not quite right. In the frequency domain, for eight points (without an...

15 days ago | 0

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How to solve Ax=B with some knowns in x and B
Hi Derek, the method below uses y instead of B so that A*x = y, and does not assume that the known values of x are contiguous t...

16 days ago | 0

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Convert permute and reshape to for
Hi Raquel, For loops are going to be slower, but it is interesting to seet how much and under what circumstances. The followin...

17 days ago | 0

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X axis for convoluted function
Hi dinesh, Here is an example with two normal (gaussian) pdfs. Arrays x and f(x) describe one of them, and arrays y and g(y) d...

18 days ago | 0

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¿Why the phase of the Fourier transform whith "angle" fuction of a rectangular pulse function is not odd?
Hi Paulina, neglecting some unimportant (in this context) real constants, the fourier transform of the square pulse is sin(w*t...

20 days ago | 0

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RF toolkit capacitance calculation
Hi Derek, The exact expression is indeed the acosh expression used in Matlab, and we would expect no less. The log expression ...

27 days ago | 0

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How to shuffle data at the same way EVERYTIME random.seed(42)
Hi RG rng(12345) % for example rand rand rng(12345) rand % same values as before rand see help rand for mor...

1 month ago | 0

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Inaccuracy in a loglog(...) plot, compared to a standard plot(...)
HI Adam, I am assuming that you are doing something like x = [1 2] y = [2,3] plot(x,y) and then zooming in on the plot at, ...

1 month ago | 3

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Answered
I'm not getting antenna pattern roll off that I expect, not sure if I'm wrong or where there is 20, there should be 10?
Hi mike, since intensity goes as the square of the E field, the expression to use is 10*log10((cosd(70)^1.4)^2) ans = -1...

1 month ago | 0

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Surf(x, y, z) with a colormap that is only two colours
Hi Emil, x = linspace(-20,20,2400); fz = exp(-x.^2./0.2).*cos(5*x); [X, Y] = meshgrid(x, x); z = exp(-X.^2-Y.^2); f = z.*me...

1 month ago | 0

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Fourier series of any function
Hello Danny, the problem is that you are supposed to approximate the function with a sum of sines and cosines with certain ampl...

1 month ago | 0

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Order of integration in double integral
Hi A.K. If you are convinced that the problem arises from the square root singularity, one approach is a change of variable y ...

1 month ago | 0

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How to integrate products of hypergeometric functions and rational functions?
Hello Nicolas, I don't know how you are implementing the nth derivative of 1/(lambda^2 + q^2) but it is obviously very time con...

1 month ago | 0

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Answered
Simplifying a complex function in order to separate real and imaginary part?
Hi zah ra, An explicit form for real and imaginary parts of (1 - r*exp(theta*1i))^(3/2) is possible, although not particularl...

2 months ago | 0

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Steady-states and non-trivial eigenvalues of equation
Hi katara, the fixed points are at 0,theta,K as you said. Although you don't have specific values, the derivatives, which you ...

2 months ago | 0

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Cannot use besselh as function handle
Hi wbriand, any reason you can't just define F = @(nu,z) besselh(nu,1,z) or F = @(nu,z) besselh(nu,2,z) whichever one you w...

2 months ago | 0

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Scaling an array by a certain number so that the area under the curve equals a fixed number
HI Christina, A = trapz(x,pyy) % find the unscaled area pyy_new = pyy*(30/A); trapz(x,pyy_new) % this ...

2 months ago | 0

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ilaplace() function is giving wrong results
Hi David, plugging in cosh(z) = ((exp(z) + exp(-z))/2 sinh(z) = ((exp(z) - exp(-z))/2 results in a constant and two exponent...

2 months ago | 0

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clamp cross-entropy loss
Hi Matt, z = log(Y); z(z<100) = 100; loss = -sum(W*(T.*z))/N; In the link you provided, they talk about a limit of -100 rath...

2 months ago | 0

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Vectorization time-varying recursive linear function
Hi Bruno, a = rand(1,50); b = rand(1,50); % method 1 xk = 0; x = zeros(1,50); for k = 1:50 xk = a(k)*xk + b(k); ...

2 months ago | 0

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Answered
Laplace of heaviside function with negative arguments
Hi Darius, since the laplace transform is Integral{0,inf} f(t)*exp(-s*t) dt, the value of f(t) for t<0 makes no difference. ...

2 months ago | 0

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Intersection line and quadrilateral
Hi Francesco Here is one way. The function linecross determines whether two line segments intersect. The function yesno just ...

2 months ago | 0

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How to find out the intersection points between two 3D ellipsoids?
Hi PA, As has been alluded to, the intersection of these two surfaces results in lines. These are calculated below. The abc c...

2 months ago | 0

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dot multiplication of the matrices is not the same when you feed the matrix and concatenate the matrix
Hi mohammed, For H1_2 you have switched a3 and a4 between the first calculation and the hand calculation. So you get two diffe...

3 months ago | 0

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About FFT of cosine function
Hi mk, In order to get just the two sharp peaks you need to have exactly n oscillations in the time domain. Otherwise the wave...

3 months ago | 0

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