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# David Goodmanson

### David Goodmanson

654 total contributions since 2012

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Checking values in a vector
Hello Jose if any(x(4:end)~=0) (do something) else (do something else) end

alrededor de 18 horas ago | 0

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solve equation whit integer output as a matrix
Hi Simon, you have z2/z1 = 3.9 % or 10*z2 = 39*z1 since 10 and 39 are relatively prime, i.e. they have no prime factors in...

2 días ago | 0

How to solve a differential equation and the plug a number in for the resulting differential equation
Hi Benjamin, syms x d = diff((1 + 5 * x^2 - 2 * x^3 + 8 * x^4) ^(1/8)) x0 = 8.8 val = double(subs(d,x0)) val = 0.2...

2 días ago | 0

System of nonlinear equations
Hi Aleem, Wolfram Alpha is solving this numercially not analytiaclly so you might as well, too. b = @(t) 10*cosd(15)*(t+ 2*(4...

4 días ago | 1

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My diff function won't work and I'm not sure why
Hi Julia, if you want to use this for a variety of functions, then fun = @(x) exp(2*sin(x)) - x; % one example [f g ...

4 días ago | 0

How to implement polyval in more than one dimension when the summation includes complex coefficients
Hi Matthew, unless I'm missing something, % make up some data M = 5; N = 6; c = rand(N,M)+i*rand(N,M); eps = .3; delt = ...

6 días ago | 0

How can I make curve form data?
Riyadh; The differences from a straight line are small, so it make sense to look at that difference. x = [7000,7050,7100,7150,...

9 días ago | 0

Does fftn do post padding ?
HI raheem, It's pre padding of the original x array by 56 in each dimension, before the fft. As you can see, the y array has n...

9 días ago | 0

Compute the difference matix between a marix and another matrix in MATLAB
Hello Jesujoba, it looks like A and B must have the same number of columns but can have a different number of rows. The for-lo...

10 días ago | 0

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Problem Using Summation Notation with Euler's Number
Hi Jonathan, symbolics is just telling you that it can't do the sum explicitly and get an analytic solution. Fortunately the t...

11 días ago | 0

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Problem in 2 dimensional numerical integration
Hi Ashok, you can make a decent case that the answer is 1/2, at least if the variables are continuous. For the first term, In...

16 días ago | 0

Bessel function - roots and zeros on interval <12,20>
HI Jaroslav Do roots and zeros mean the same thing? The code below uses Newton's method to find the roots, which has the advan...

16 días ago | 0

3D vector plot of electric field
Hello QP, Once you have made the matrix variables XX,YY,ZZ, those are the ones you use for further calculation, no longer x,y,z...

18 días ago | 0

Plotting a matrix of co-ordinates
Hi Anmoi, points = rand(2,56) plot(points(1,:),points(2,:),'o') grid on If you go to the help for plot you will find many ot...

18 días ago | 1

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Matrix division problem on adding condition
Hi David, MODIFIED the solution is not immediate, but you did ask … Take the example A = [1 2 3] C = [5 2 -1] B = the matr...

20 días ago | 2

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Evaluating svd() on slice of matrix array.
Hi Morten I take it that your matrices are close to being orthonomal already. Try [Q, ~] = qr(A(:,:,i)); A(:,:,i) = Q; whic...

25 días ago | 0

How to solve a system of linear equations with strict inequalities and equalities?
Hi Terri, Looks like it is not possible. You have [F1;F2;F3] = [10 2 10 15 20 8 6 4 12] * [x1;...

25 días ago | 0

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How can I solve for the matrix S in the below mentioned matrix equation?
Hello NAA, It appears that you mean that d is 3x6,not 6x3. Let E = EPS_T - EPS_S and abbreviate inv(S) as iS. You are looki...

26 días ago | 1

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How do i scale to my axis after fft?
Hi Cherie, you have a time array of length, 601 and spacing deltat = .01. The frequency array is going to be 601 points with t...

27 días ago | 1

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Raise the elements of a matrix to a power.
Hi Ricardo, min3 = min.^3 It's not a good idea to name a variable 'min' because that is the name of a built-in Matlab function...

27 días ago | 1

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Solving an equation with terms that require double summation and products
Hi GS, I reproduced your results and then calculated the equation using for loops, just to make sure, and got 1.8767e37, same a...

27 días ago | 0

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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...

28 días 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...

29 días 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...

alrededor de 1 mes 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...

alrededor de 1 mes 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...

alrededor de 1 mes ago | 1

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

alrededor de 1 mes 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 ...

alrededor de 1 mes 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 ...

alrededor de 1 mes ago | 0