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# David Goodmanson

### David Goodmanson

633 total contributions since 2012

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Solving an equation with terms that require double summation and products
Hi GS, try aij_2 = aij.^2 Since y1 and y2 are scalars, there are three dots in the last equation that you can drop. I usuall...

ongeveer 13 uur ago | 0

How to plot double sided amplitude spectrum after FFT?
Hi Hamid, at the end of your code I added the following: figure(2) plot(f,fftshift(cmag),'o'); grid on xlim([-30 30]); f...

2 dagen ago | 0

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Why are the symbolic units not evaluated by a square root?
Hi Lucas, try your original code but with the last two lines omega_n = (pi/l)^2*(g*E*I/(A*lambda))^(1/2) omega_n = vpa(simpli...

7 dagen ago | 0

how to calculate direction in rotated coordinate system
Hi UWM, Assuming the correct rotation has already been made, then calling the resulting vector u, and making sure it is normali...

8 dagen ago | 0

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Why did i get different answers for eigenvectors for different powers of a matrix?
Hi RMT, Since you have two identical eigenvalues, the eigenvectors corresponding to those eigenvalues are not unique*. They on...

8 dagen ago | 1

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Element-Wise Vector Division
HI Mark, new_vector = K./vector; ./ (dot divide) does element-by-element operations.

11 dagen ago | 1

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Vectorizing the addition of a vector of values with associated indices to an existing vector, when the vector of indices has repeated values.
Hi Nathan, sparse matrices automatically do what you want. You have full matrices, and sparse operations are on the slow side ...

11 dagen ago | 0

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Sub-sampling the minimum number of points to accurately reproduce a curve
Hi Michael, take a look at the interp1 function. There are several choices for the type of interpolation, and assuming a curve ...

11 dagen ago | 0

Cannot find ALL solutions to simultaneous equation
Hi CZ If exp(x^2+y^2+z^2) = 9 then x^2+y^2+z^2 = log(9) which is a lot less challenging for symbolic evaluation. clear all...

12 dagen ago | 0

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Troubles assigning colorbar values in a bivariate histogram plot
Hi Mar, I have been looking at this with some data I made up, but now that you posted it I was able to plug it in. I thought y...

12 dagen ago | 0

What to use instead of simple function?
Hi Liliana, 1/(2*pi^(1/2)*(1/(4*a^2))^(1/2)) may not be pretty, but it does equal a/sqrt(pi) so it is mathematically correct....

22 dagen ago | 0

a Simple Matrix question
Hello LC Matrix_C = matrix_A; Matrix_C(matrix_A == Matrix_B) = 255;

24 dagen ago | 0

How can I get more than 49 digits of pi in a string?
Hi India, vpa(pi,100) for example (although you need the symbolic toolbox for vpa) And see Walter's comment below. The answer...

25 dagen ago | 0

plot polygon function error
Hi msh, the reason is pretty simple. You are asking for an output from the function, but you have not provided any in its defi...

29 dagen ago | 0

why the legend show wrong lines ?
Hi tomer, try replacing plot(t,43*(19.6e-3)/(100*15e-3),' black '); %% plot--> of boundery limit with plot(t,43*(19.6e-3)/(...

29 dagen ago | 0

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Solving 3 Simultaneous Exponential Equations
HI Rory, just for completeness y1 = 159.2543; y2 = 117.2699; y3 = 63.8384; x1 = 291.15; x2 = 293.15; x3 = 299.15; A1 =...

30 dagen ago | 1

solve on vector equation
Hi Michiel, The unit vector N has to lie in the plane defined by s1 and s2. The result for any s1,s2 is N = s2 - (n1/n2)*s1;...

ongeveer een maand ago | 0

how can I creat a matrix of all possible combinations of zero and ones across eight digits.
HI Yonatan, not a black box: function a = x10(ndigits) a = ['0';'1']; count = 1; while count < ndigits n = size(...

ongeveer een maand ago | 0

IFFT of Convolution equivalence
Hi JOB/Ridwan Here is a small example where a and b are padded with zeros, so that regular convolution can be compared with con...

ongeveer een maand ago | 1

Why 999^999-999^999 is NaN?
HI Fahmy, >> realmax ans = 1.7977e+308 That's the largest floating point number in Mallab, which uses IEEE754 64 bit double ...

ongeveer een maand ago | 0

How to obtain CDF from the below PDF function
Hello Manesf, This pdf seems related to the Weibull distribution. I made some abrreviations Etta_d = xid Etta_D = xiD ...

ongeveer een maand ago | 1

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In the matlab page of Associated Legendre Polynomials, is the example for the spherical harmonics correct?
Hi chaitanya, Good catch. Really good catch. In addition to the signs of the lobes, I believe that Matlab's Y32 is functional...

ongeveer een maand ago | 2

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How to plot the velocity of a crate on a ramp for different angles?
Hi Kiera, The plot above shows the velocity of the box at the top of the ramp getting larger as the angle of the ramp gets stee...

ongeveer een maand ago | 0

associated legendre functions matlab
Hi chaitanya, It's apples and oranges. When the domain of the argument is -1 <= x <= 1, the function is -sqrt(1-x^2). That's ...

ongeveer een maand ago | 0

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Implementing a sum with summands of unequal spacing inside an integral
Hi Richard, I don't claim to be a professional although I did use Matlab at work, and here is how I would do this. The main th...

ongeveer 2 maanden ago | 1

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Does the permute function have a bug?
Hello ZY, see 'help permute'. Permute puts the dimensions in the order listed, so in this case the old 4th dimension goes firs...

ongeveer 2 maanden ago | 0

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Is it possible to create periodic boundary conditions for a matrix with linear indexing?
Hi Tom, mod(k,N)+1 for the raised index, k+1 mod(k-2,N)+1 for the lowered index, k-1 and these do give the correct vector of ...

ongeveer 2 maanden ago | 0

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how to solve the equation: xdot=AX+Bu; where u=sin(2t)
Hi Ebraheem, ode45 is fine with explicit time dependence in the calculation of xdot: [t, x] = ode45(@smc5,[0, 10],[1, -2]) pl...

ongeveer 2 maanden ago | 2

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