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# J. Alex Lee

Last seen: ein Tag ago Active since 2016

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I am trying to find the exact distance of a curvy line.
Assuming that the boundary points are ordered well (adjacently), then you can calculate the cummulative square distance between ...

2 Tage ago | 0

Take only some values from one array
you can't compare arrays of different lengths. a straightforward but cumbersome way is to cycle through each of your t1 and find...

7 Tage ago | 0

MATLAB GUIDE to App migration question
Apparently it should work: https://www.mathworks.com/help/matlab/creating_guis/compatibility-between-different-releases-of-app-...

17 Tage ago | 0

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How to Save new data to existing structure data in a for loop without having to save the complete Matlab file from Zero?
I would consider using a database, a lightweight solution could be sqlite. I use the third party mksqlite for this purpose and i...

23 Tage ago | 0

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...

etwa ein Monat ago | 0

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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...

etwa ein Monat ago | 0

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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...

etwa ein Monat ago | 0

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 ...

etwa ein Monat ago | 1

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...

etwa ein Monat ago | 0

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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...

etwa ein Monat ago | 0

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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...

etwa ein Monat ago | 1

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...

etwa ein Monat ago | 0

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 ...

etwa 2 Monate ago | 0

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...

etwa 2 Monate ago | 0

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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...

etwa 2 Monate ago | 0

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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(...

etwa 2 Monate ago | 1

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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...

etwa 2 Monate ago | 0

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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...

etwa 2 Monate ago | 2

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...

etwa 2 Monate ago | 2

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

etwa 2 Monate ago | 0

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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...

2 Monate ago | 0

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...

2 Monate ago | 0

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...

2 Monate ago | 1

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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...

2 Monate ago | 0

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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...

3 Monate ago | 0

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...

3 Monate ago | 0

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...

3 Monate ago | 0

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)

3 Monate ago | 1

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