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# David Goodmanson

### David Goodmanson

738 total contributions since 2012

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Fast Fourier Transform component detection issue
Hello awezmm, This occurs because of a combination of aliasing and the spacing of the chosen frequencies. For sampling frequen...

environ 22 heures ago | 1

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My code won't run, related to ode function
Hi Dardenella, try the same thing only with [t,Y] = ode45(@(t,Y) f(t,Y,omega0,p), [0,10],[y0,v0]); % solve for 0<t<10 [n...

2 jours ago | 0

How to make specific elements in a 3D matrix zero?
Hi Rabia, try for yy=1:10 temp = Costyearlydata(:,:,yy); temp(D(:,1,yy)) = 0; cost1(:,:,yy) = temp; end

3 jours ago | 0

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constructing a difficult large matrix
Hi ektor, I presume you are interested not so much in the in the matrix A as in the 1000 scalars you get after you multiply eac...

3 jours ago | 0

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Plot the travel for an electron by using ode45 (involving matrices)
Hi Ibrahim, There is nothing wrong with using matrices in this situation, and the plot is fine, insofar as it is plotting what ...

3 jours ago | 1

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Solver Equation not giving solution
Hi Diogo, Matlab syms can solve this, but it needs some help, which is squaring both sides of eqn3 to form a new eqn3. Also si...

4 jours ago | 0

Mutual Inductance ODEs and wireless power transfer
Hello Tucker, You have two first order DE's so there is no need to have a vector x with four components. Four is appropriate f...

4 jours ago | 0

Can anyone help me to fix my code?
Hello JCam, Since you are looking for a numerical result there is really no reason to use syms here. With x and y both being 1...

5 jours ago | 0

Strange disagreement between analytical phase and unwrap(angle())
Hello Joshua, There a a couple of issues with the analytic calculation. Xkabs = abs( Ampl*sin((pi*L/N)*(k-1)*dn)./sin((pi/N...

6 jours ago | 0

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Plotting complex roots of polynomial
Hi Thomas, what the roots function is looking for is the coefficients of the powers of z in decreasing order. In this case tha...

7 jours ago | 0

Problem with cholesky decomposition
Hi Peter, when you use the 'lower' option, chol assumes that the upper triangle is the complex conjugate transpose of the lower...

7 jours ago | 1

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Refractive index profile calculation
Hi Tay, The following code addresses (1) in the text. For Lf = 1, D = 1 and 1000 layers the resulting plot reproduces the one ...

7 jours ago | 1

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Swapping the columns of a matrix with every other column
Hi Robert, Going with permutaions of the first six columns in conjuction with permutations of the last four columns certainly r...

8 jours ago | 1

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How to find all the non unique solutions in rank deficient system of linear equations in matlab
Hello Zeab, One solution is v0 = A\b. Since A is rank defiicient it has a nonempty null space nullA = null(A) which is dime...

11 jours ago | 1

How to solve coupled ODE problem
Hi seoyeon, It's easy enough to solve for Ydot4 in the fourth equation. Then if you put that up front in the code, you can plu...

15 jours ago | 0

How to extract the coefficient of x inside the exponential?
Hi Ishan, Squaring y gives 16 terms involving the product of two exponential functions. Multilying exponentials means adding t...

16 jours ago | 1

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How to copy colormap from an existing image
HI Alexei I copied the image you provided as a jpeg, used datatips to find coordinate points at the top and bottom of the color...

18 jours ago | 0

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Taking an average of every n elements of one column
Hi Tony, a = rand(144,73,551); b = squeeze(a(:,3,:)); % take all the third columns c = mean(reshape(b,12,[])...

18 jours ago | 0

Integration of a vector with hyperbolic function
Hi Sunit, Thanks for annotating the code and providing the expressions as comments. The key here is with the C1 coefficient...

18 jours ago | 1

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After the FFT(Frequency-Amplitude) of the seismic wave(Time-Acceleration), I want to reconstruct the seismic wave(Time-Acceleration) by IFFT again.
Hello haeyeon, A couple of things here. First of all, you are using nextpow2 to go from what looks like 10001 points to 16384....

19 jours ago | 0

How do you do a radial Fourier transform in MATLAB?
Hi S, here is one way. First of all, the transform pair is q*F(q) = Int r*F(r) sin(q*r) dr r*F(r) = (1/(2*pi))*In...

19 jours ago | 0

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FFT and PSD - normalize values
Hi John, This concerns fft only; psd is a different animal. For a continuous oscillation, most people do not seem to be concer...

19 jours ago | 0

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Problem with using symbolic integration
Hello Yasho, For any reasonable q, integrating from l to u gives F = 1 by definition of the beta function. When q is an intege...

20 jours ago | 1

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Time of sparse matrix components allocation
Hi reza, with sparse matrices you want to build up a set of indices to use in the first two inputs, in order to make a single c...

23 jours ago | 0

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Matrix differential equations, correct answer?
Hi Sara, this plot figure(1) tvec = 0:.01:6; reliability_d = double(subs(reliability,t,tvec)); rel_d = double(subs(rel,t,tv...

24 jours ago | 1

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Plotting a section of a hemisphere using parametric equations
Hi Marcus theta=[0:0.01:1]*2*pi; ensures that the value of 2*pi is reached.

26 jours ago | 0

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Trying to solve time of charge of supercapacitor with ode45
Hello Isaac It seems easier to do this as two first order equations for the node voltages V1 and V2 rather than go to a second ...

26 jours ago | 0

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How to use one ode45 to solve another?
Hi Carlos, you can toss them all in together, with g(1) = y(4) and g(2) = y(5). That way y(1) is available in context. t0=0; ...

27 jours ago | 0

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Warning: Matrix is singular to working precision.
Hi y, In the future it would help if you copied in text rather than an image, so as to make it easy to run without retyping. I...

28 jours ago | 0