# J. Alex Lee

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**Content Feed**

Implementing Crank Nicholson in spherical setting

I believe this should be the right formulation for CN (taking a few liberties interpreting your problem). If you want speed, pr...

4 mesi ago | 0

Implementing Crank Nicholson in spherical setting

For one thing, your boundary conditions (as developed on your pdf) don't look right. At r=0, you can just directly use Eq 8 LHS...

5 mesi ago | 0

Question

Built in look-up style interpolation of timetables for non-numeric data?

Is there no built-in function similar to interp1 for numeric data, that can operate on timetables with arbitrary data types? So...

5 mesi ago | 1 answer | 0

### 1

answerFor loop to carry value down depending on another matrix value

In your example, there is a "delay" by 1 row when your switch from 0 to -1 occurs, so the following answer is not exactly produc...

6 mesi ago | 0

| accepted

There used to be a function RefineMesh in Matlab used in solving ODE's, but it is now used for PDE's and isn't the same function. Is there a new function for the old purpose?

The workflow above only re-evaluates the "static" solution of ode45 at more data points by an interpolation scheme consistent wi...

9 mesi ago | 0

Is there a way to measure interletter spacing for Fixed Width font in MATLAB?

I have no idea what you mean by "visual angle per font size", but I know of one way: lbl = uicontrol("Style","text","String","...

10 mesi ago | 0

Functional programming construct to expand cell array into arguments for other functions without using an intermediate variable in the (user) code?

I am still not sure why you can't just have your generalized comparator function saved as a function somewhere on your path so y...

12 mesi ago | 1

How to integrate uidatepicker command with GUI interface?

Details are thin here...but it sounds like you need to first specify the parent graphics object that you want your uidatepicker ...

12 mesi ago | 0

How to solve exponential equation to find unknown constants

data = readtable("Book1.xlsx"); Alternatively, based on my reparameterization above you can as a first pass say everything afte...

circa un anno ago | 0

| accepted

How to solve exponential equation to find unknown constants

Do you have an intuition of what the graph of looks like? Hint: it looks like your plot, scaled and shifted roughly only in the...

circa un anno ago | 0

Print vectorized graphic of patches without edges

I now believe it is because you are technically plotting 3D patches (telling Matlab there's a z-coordinate, even if they are all...

circa un anno ago | 1

Calculations of Angle between two points

If you have the list of 3D coordinates rng(1) % control random generator NPoints = 5 vertices = rand(NPoints,3) You can defi...

circa un anno ago | 0

How to symbolically integrate f(T) = exp (E/(8.314*T) through integration by parts or with trapezoidal method?

The application still is unclear to me... If you just want numerical integration, look at the function "integral", as implement...

circa un anno ago | 0

Remove zoom from axes

This should be a good entrypoint: https://www.mathworks.com/help/matlab/ref/disabledefaultinteractivity.html https://www.mathw...

circa un anno ago | 0

Can I pass arguments to a @callbackFcn?

configureCallback(s,"terminator",@(src,evnt)readSerialData(src,evnt,operation mode)) So the first parentheses specify the inter...

circa un anno ago | 1

| accepted

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 ...

circa un anno 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...

circa un anno 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-...

circa un anno ago | 0

| accepted

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...

circa un anno 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...

circa un anno ago | 0

| accepted

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...

circa un anno ago | 0

| accepted

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...

circa un anno 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 ...

circa un anno 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...

circa un anno ago | 1

| accepted

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...

circa un anno ago | 0

| accepted

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...

circa un anno ago | 1

| accepted

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...

circa un anno 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 ...

circa un anno ago | 0

| accepted

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...

circa un anno ago | 0

| accepted

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...

circa un anno ago | 0

| accepted