John D'Errico

Retired

Last seen: Today | Active since 2006

Followers: 28 Following: 0

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A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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Answered
Why is vpa not converting double accurately?
Quite interesting. When I first saw the title, I assumed it would be an obvious mistake. Then I saw the poster, and knew it woul...

ongeveer 15 uur ago | 0

| accepted

Answered
finding partial solutions from ill-conditioned equations
The largest subset? It may be impossible to compute ANY subset accurately. You may be able to only compute a linear combination ...

3 dagen ago | 0

Answered
What is evaluated to standard output is not being assigned to my variable
This is a not uncommon misunderstanding about cell arrays. d = {'.'; '..' '2022' '2024' '2025'} b = d(3:end) % the "righ...

9 dagen ago | 1

| accepted

Answered
Create similar curves through specific data points
The question is becoming more clear now, based on your response to my first answer. I'll post this as a separate answer, since t...

19 dagen ago | 0

| accepted

Answered
Create similar curves through specific data points
You have asked a confusing question, which usually means you are yourself confused, perhaps about what you really want to do. It...

19 dagen ago | 0

Answered
Solving linear system modulo prime^n when matrix is univertable
You can't use LU anyway, since it is not designed to work on that problem. Nor can you use slash or backslash, which again, do n...

21 dagen ago | 0

Answered
Differentiating inside a matlab function
Oh, you were so close. Actually, you did not even need to tell diff what variable to differentiate with respect to. syms x(t) ...

23 dagen ago | 0

Answered
How to generate an prime random number??
A random prime? Impossible to do. That is, something that many seem to misunderstand is you cannot generate a random number on s...

24 dagen ago | 0

Answered
How to make multiple lines of best fit into one scatter graph
Is it possible to do in MATLAB? Of course it is. It of course depends on the skill of the person writing the code. It depends on...

24 dagen ago | 0

Answered
Find best fit curve from multiple curves of different size
On the right end, you have an infinite slope. On the left end, not so much of a problem. But it will be better to do a couple of...

25 dagen ago | 0

Answered
How does interp1 work?
Why not post the actual data you used that caused the problem, instead of only a tiny fragment of it? You certainly CAN post t...

25 dagen ago | 2

Answered
Matlab Dimpulse function documentaion not found
It seems dimpulse (or at least one version thereof) can be found in the control TB. which dimpulse -all However, given the loc...

26 dagen ago | 0

Answered
part 3 example was wrong
Answers is not official MATLAB support. So telling us a problem exists does nothing. Contact support directly. https://www.ma...

28 dagen ago | 1

Answered
I'm trying to find solutions to variables in a system of non linear eqations, that represent a geometrical puzzle.
A problem is, we don't actually know what is the geometric system you are trying to solve, nor have you told us the solution you...

28 dagen ago | 0

Answered
Integrating a very long expression containing symbolic values
Is there some law of mathematics that everything you can or will write down has a solution? (No.) That int did not find a soluti...

29 dagen ago | 0

Answered
Can someone help me fix my bisection function?
Good code. Well, at least in terms of the documentation. Excellent in that respect. Readable code is important when you need to ...

30 dagen ago | 0

| accepted

Answered
What is the interpolation algorithm behind MATLAB’s pcolor with FaceColor = 'interp' that creates sharp, defined boundaries？
There are three simple ways to interpolate inside a 2-d rectangular region. But two of them are analogues of each other. First,...

30 dagen ago | 0

Answered
How to compute the characteristic equation given the eigenvalues?
You have not asked this question as if it is a homework assignment, so I'll give an answer. The characteristic equation GIVEN e...

ongeveer een maand ago | 0

| accepted

Answered
How to download old version of toolbox?
You cannot. That is, you cannot use an old toolbox for a previous release in a newer release of MATLAB. So what can you do? You...

ongeveer een maand ago | 0

Answered
Bug with large HEX numbers
H = 'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141'; numel(H) So 64 hex digits, which would yield an intege...

ongeveer een maand ago | 1

Answered
How to get consistant results when testing code performance
A single time test will be susceptible to anything that attracts the attention of your CPU. And sadly, your CPU suffers from com...

ongeveer een maand ago | 0

Answered
update guess in fsolve
Um, no, You cannot always find a way to "update" your initial guess for fsolve. One can even prove this to be true. You can cha...

ongeveer een maand ago | 1

Answered
How to remove columns in very large matrices.
GET MORE RAM!!!!!!!!! RAM IS CHEAP!!!!!!!! Need I say it again? You have a quite large array. (1.75e6*2000*8)/1e9 That arra...

ongeveer een maand ago | 1

Answered
using sparse matrix and vpa function simultaneously
I wanted a nice bright red Lambo for Christmas. Nope. Did not happen, nor was it ever going to happen. The same applies to you. ...

ongeveer een maand ago | 0

| accepted

Answered
Matrix is singular to working precision
I don't even need to run your code, to see an obvious mistake. In fact, I knew what I expect to be a problem, even before I look...

ongeveer een maand ago | 0

Answered
real and integer variables
No. We won't do what is surely your homework assignment. But why not TRY IT! First, plotting it is trivial. LEARN TO USE a tool...

ongeveer 2 maanden ago | 0

Answered
Why matlab is not as intelligent as python
Why? Why is anything the case? Because it is. Because they are two different languages, with different capabilities, and differe...

ongeveer 2 maanden ago | 3

Answered
Matlab sparse matrix does not come out as I would expect
S=sparse([1 3 2 1 4],[3 1 4 1 4],[1 2 3 4 5],4,4) full(S) It works just fine. What did you do wrong? LOOK CAREFULLY AT WHAT Y...

ongeveer 2 maanden ago | 1

| accepted

Answered
defining upper and lower limits of a matrix
Is there any way to set the min and/or maximum values of the elements in a matrix, and do so automatically? NO. Well, not withou...

ongeveer 2 maanden ago | 1

Answered
how to optimize block toeplitz matrix ?
The one thing you NEVER, EVER, EVER want to do is stuff the elements into a sparse array iteratively. NEVER DO THAT!!!!!!!!!!!!!...

ongeveer 2 maanden ago | 0

| accepted