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J. Alex Lee


Last seen: Today Active since 2016

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Answered
using varfun on a timetable with subscripts?
first of all, your operation looks like a "diff", no subscripts (for rows, i.e., timestamps) necessary second, you will be defi...

1 day ago | 0

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Answered
How can I quickly obtain the inverse of a square sparse matrix?
potentially, if you have more information about the properties of A, you can specify them in a call to linsolve https://www.mat...

1 day ago | 0

Answered
3D/2D matrix multiplication without using a loop
I found this: pagemtimes() s = rand(5,5); x = rand(5,8,100000); tic y = pagemtimes(s,x); toc tic z = nan(size(x)); for...

7 days ago | 0

Answered
How to operate properly with multidimensional matrices and cells.
You might be looking for squeeze()? l=0; % preallocate C = cell(3,3,3); M = nan(3,3,3); % construct 3D cell and matrix ...

10 days ago | 1

Answered
How to solve a system of second order nonlinear differential equations with boundary conditions
This is a boundary value problem, so probably the most straightforward way is to use bvp4c or bvp5c if you want to solve numeric...

12 days ago | 0

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Answered
Backward and Central Difference
I guess the answer depends what you want to do with those finite difference approximations. If you want to use it in an algorith...

12 days ago | 0

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Answered
Save class object as struct
Look at this too: https://www.mathworks.com/help/matlab/matlab_oop/flexible-saveobj-and-loadobj-pattern.html I think it means w...

12 days ago | 1

Answered
Can't get string to datetime conversion to work
str = '2019-05-17T19:36:00'; fmt = 'yyyy-MM-dd HH:mm:ss'; b = strrep(str,'T',' '); disp(b); timestamp = datetime(b,'Inpu...

12 days ago | 0

Answered
Auto Refresh in app designer.
in general for "auto refresh" you can use the timer object to schedule recurrent execution - disclaimer i have only played with ...

18 days ago | 0

Answered
Using Hessian for least squares problem
Now that the actual question is clarified as a coding question and not a math question, it seems these should help: https://www...

18 days ago | 0

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Answered
Select rows in a given table according to 3 criteria
This is small enough you could generate the full list of combinations % generate all combinations alltriplets = nchoosek(1:7,3...

19 days ago | 0

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Answered
Iterating array of chars and saving to table or cell
Try this, if your function actually returns strings as your output suggests (rather than a char array) result = strings(length(...

19 days ago | 1

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Answered
Interpolate X-Y coordinates with variable velocity to specified sampling frequency
I don't think you need loops...so assume your data is called XYV, and according to how you describe, I guess the last velocity p...

21 days ago | 0

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Answered
How to interpolate between two adjacent points of time series data, if the difference between any two consecutive points is greater than 25 by using for loop?
If you just want the points to be "appear" roughly evenly distributed, you could consider spacing in the arc length (although yo...

27 days ago | 2

Answered
How to interpolate between two adjacent points of time series data, if the difference between any two consecutive points is greater than 25 by using for loop?
Here's [another approximate] way to do it that will only call spline once (could as well do it with gridded interpolant) The me...

27 days ago | 2

Answered
Randomly selecting images from a directory
Use "dir" and "randperm"

30 days ago | 0

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Answered
Why won't cells populate via if-else statements?
The if statements are probably your problem...you are comparing a column vector with scalars, which off the top of my head I don...

1 month ago | 0

Answered
Grouping age data into 5 year bins
Interesting, this could be useful for me too! You can use "discretize" to bin the data. Below is a quick and dirty class to impl...

1 month ago | 0

Answered
How to vectorize the following code for matrix insertion?
There is a minor point in David's answer, which is that not all index collisions are taken care of in how the g matrix is constr...

1 month ago | 1

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Answered
How to rotate 3D matrix?
it looks like your segment A is parallel to the axis OA (trivial in y-direction), in which case it should be easy to first trans...

1 month ago | 0

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Answered
1-D Temperature Gradient
your time and space point vectors are t = 0:0.005:50; % but this gives you 10,001 points, not 10,000...so you decide what you h...

2 months ago | 0

Answered
how to find the order of convergence
It sounds like you already implemented Newton's method, so just save all your residuals and plot [the log of norm] versus the pr...

2 months ago | 0

Answered
Saving each vector of an ode45 vector solution in a matrix.
Use a cell array instead z = cell(1,20) for i=1:20 G=i/20 %Saving that iterates value of G [phi,y]=ode45(@(phi,y) od...

2 months ago | 0

Answered
How can I generate values randomly from another existing vecor?
how about v1 = [122,34,20,5,21] v1a = [0,v1] N = numel(v1a) ridx = randi(N,size(v1)) v2 = v1a(ridx)

2 months ago | 1

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Answered
Probelm with web app server
@Martin Andersson, hope you have resolved this by now as it has been over a month, but if not, check your windows service accoun...

2 months ago | 0

Answered
How to find duplicate file names(same name but different folder address), and write those files in excel with their respective folder address?
Here's a way that doesn't require as many loops and calls to ismember % % uncomment to simulate the results of dir and test % ...

3 months ago | 0

Answered
Get all allowed values of a class property
Ah, I should more fully embrace the validator mechanism. Here is a way by defining a custom validator, so in a way less hard-cod...

3 months ago | 2

Answered
web() and inputdlg() in App Designer
i think you can get around both limitations with some extra coding...never tried it, and just a thought, but... you could proba...

4 months ago | 0

Answered
Want to connect 3D scattered data points with line
On way is to do it in a loop. After your code, hold on d = zeros(size(x)); % to hold distances from the first point for i =...

4 months ago | 1

Answered
Concentric Squares with matricies
Try looking into padarray (or arraypad I can't remember...). I think you can apply successively to achieve what you want

4 months ago | 0

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