# L'O.G.

Active since 2022

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Question

Using accumarray to sum all values associated with a given node
Given a graph with the following edges edges = [1 2; 2 3; 3 1; 2 4; 4 5; 4 1]; I have some data associated with each edge dat...

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Question

Numerical first derivative of irregularly spaced data
Given a vector x and a vector y, the numerical first derivative should be gradient(y)./gradient(x) for all points specified by x...

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Solving an initial value problem when one of the initial values is unknown
I am trying to numerically solve the ODE given by a*y"(t) + b*y'(t) = c, where a, b, and c are positive constants. I set this up...

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Question

How do you set up an ode solver with a more than one function in the ode?
For example, if you have an ode such as a*df(t)/dt + b*dg(t)/dt + f(t) + g(t) + c = 0 that you'd like to solve and if you want t...

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How do you solve a coupled ODE when one of the ODE results in a vector of length 3 and the other results in a scalar of length 1?
For instance, in the following example that I found online, if dz(2) were actually a vector, how would you modify this? [v z]...

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How to call an ode solver within another function?
I solve dx/dt = x(t) using an ode solver sol = ode45(@(t,x) u(t,x,ode,eps,a0),[t0 tf],[x1;x2]); that calls a function u fo...

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Question

How to do this unusual Fourier transform?
I am trying to compute a sine transform: I'm not sure about the non-standard bound of the integral (why it's not infinity...

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Solving linear systems in Matlab
How do I solve for x in u = A(x+b)? A is a matrix, and the other terms are vectors. Isn't it something like x = A\u - b ? I'm no...

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Runge-Kutta with a function that changes at each time step
I previously asked a question about solving an equation dx/dt = u(x,t) where u(x,t) is a velocity. I want to solve for the posit...

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Question

Using Runge-Kutta in Matlab
I am trying to solve an equation dx/dt = f(x,t) where f(x,t) is a velocity. I want to solve for the positions x to obtain the tr...

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Question

Integrating a constant?
This is more of a physics question than a Matlab question, but given an instantaneous velocity vx and a time increment dt, how d...

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Question

Numerical integral where the bounds change with each evaluation
I'm trying to take the following integral: I tried this symbolically, but I think that was throwing me off. I am attachin...

ungefär ett år ago | 1 answer | 0

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Question

How to take an integral symbolically and then convert it to type double?
How do I take the following integral symbolically? And convert it to double? I have a 1000 x 1 numeric vector of type double for...

ungefär ett år ago | 1 answer | 0

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Question

Inverse of a matrix
I want to solve the following for X2: A = B(X1+X2) where B is a matrix, and A, X1, and X2 are vectors. I can't divide by a matri...

ungefär ett år ago | 1 answer | 0

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Question

Integration when some of the values change over time
I have a function of the form where is the position of the k-th object and is the corresponding force. The force has a functio...

ungefär ett år ago | 1 answer | 0

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Question

How can I detect the object in this noisy image?
I'm trying to process images like the attached. In this case, there should be an object near the center of the image around test...

ungefär ett år ago | 2 answers | 0

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Question

Cell arrays with a vector within a cell within a cell
I have a cell array where each element consists of a 1 x 1 cell containing a vector of type double, i.e., C{1,1} contains a vect...

ungefär ett år ago | 3 answers | 0

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Question

How do you convert the cell within a cell to a vector?
I have a cell of cells. The inner cell is a 1 x 1 and contains a vector. The vector in each inner cell might be of different len...

ungefär ett år ago | 1 answer | 0

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Question

How to output a cell array as a table where the arrays contain vectors of different length?
I have a cell array C that is 3 x 10, with each element containing a vector of numbers of type double. Each vector is of a diffe...

ungefär ett år ago | 2 answers | 0

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Question

Working with cell arrays
I would like to separate columns in an array based on the unique values of the first column. I think the way to do this is a cel...

ungefär ett år ago | 1 answer | 0

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Question

How do I read each frame of a video?

ungefär ett år ago | 2 answers | 0

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Question

Finding first value in an array equal to each number in a vector
I can find the first value in test_array that is equal to 2 using the following: find(test_array==2, 1, 'first') But how d...

ungefär ett år ago | 1 answer | 0

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Question

What is the previous syntax for this function?
I can combine strings using something like str = append("Hello","world") But I have access only to Matlab 2018a. The append fu...

ungefär ett år ago | 1 answer | 0

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Question

How to remove repeating entries from a vector?
How do you remove repeating entries in a vector? For example: A = [1 1 1 0 0 1 1 1 1 0 0 0 0 0] should return B = [ 1 0 1 0]....

ungefär ett år ago | 1 answer | 0

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Question

Vectorization problem for grouping entries in an array
The data below are grouped into three different subgroups based on the value of B(:,3). If, however, B(:,2) <= 1, how do I indic...

ungefär ett år ago | 1 answer | 0

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Question

How do you reshape an array to preserve the order in each row of the original array?
How do you reshape an array into a 1-dim column such that the first row of the original array is the first set of numbers in the...

ungefär ett år ago | 1 answer | 0

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Question

How do you set entries in a matrix for odd rows with odd columns to zero?
I want to set A(i,j) = 0 if both i and j are odd. Is this possible to do vectorially?

mer än ett år ago | 1 answer | 0

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Question

How do you make the diagonal and certain off-diagonal elements of a matrix zero?
I have a square matrix and would like to make the diagonal elements zero, as well as select elements that are off-diagonal. For ...

mer än ett år ago | 2 answers | 0

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Question

x values when taking a numerical derivative
I want to calculate the first derivative f(x) = dy/dx for data that is irregularly spaced in x. I think (correct me if I'm wrong...

mer än ett år ago | 5 answers | 0

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Question

Changing the position of a plot
How do you move everything in a figure (plot, axes, axis labels) up while preserving the aspect ratio of the plot? It seems I ca...

mer än ett år ago | 1 answer | 0