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John D'Errico


Retired

Last seen: Today Actif depuis 2006

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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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Réponse apportée
vpasolve does not solve simple equation
Well, look more closely at your question. Plot it. syms x; A = 6.742; B = 4.82; F = A - 2/(9*(1 - x)^(1/2)) - B*x fplot(F,[0,...

10 jours il y a | 0

| A accepté

Réponse apportée
Any way to remove terms smaller than "digits" from symbolic expression? R2023a
While the solutions offered by @Paul and @Walter Roberson will both solve the problem you asked, be careful, as automatic approa...

23 jours il y a | 0

Réponse apportée
When I use nlinfit, the sintax nlinfit(t0,p0 ,@(b,t) ...),but if Ireplace nlinfit with fmincon, the sintax is not valid, why?
@Marcos there is no need to use global variables. For example... x = rand(20,1); y = 3 + 4*exp(x*1.5) + randn(size(x))/3; plo...

environ un mois il y a | 0

Réponse apportée
Como puedo reiniciar mis cursos
"I took a course last year, completed it, and received the corresponding certificate. However, I need an updated certificate for...

environ un mois il y a | 1

Réponse apportée
Mixing name/value pair syntax
I have at least a couple of reasons why, which is why I will pose this as an answer. Knowing exactly which deliberations were ma...

environ un mois il y a | 0

Réponse apportée
**How can inflection points be robustly identified on a cumulative histogram (CDF) curve in MATLAB when only discrete, noisy CDF data is available?**
I'm sorry, but you are looking for magic that does not exist. An inflection point is a point where the SECOND derivative chang...

environ un mois il y a | 1

Réponse apportée
Convex bivariate B-spline by construction (PSD Hessian)?
Even without thinking about it, I'm pretty sure the answer is no. Things get nasty when you move beyond one dimension, and 2d is...

environ 2 mois il y a | 0

Réponse apportée
An easy way to input song chords into a structure of MATLAB
AVOID the function input. It only hurts your code, preventing you from growing. Learn to use other solutions for data input. One...

environ 2 mois il y a | 2

| A accepté

Réponse apportée
I'm using a 2020 Mac Mini. Will R2017a run on this computer if I upgrade to MacOS Tahoe?
No. 2017a will NOT run on Tahoe. Just read the docs to tell you which OS versions can run R2017a. https://www.mathworks.com/co...

environ 2 mois il y a | 0

| A accepté

Réponse apportée
Are iterative methods always better than direct methods for solving large linear systems?
The use case which some may miss here, is the very large array, where a dense solver fails due to memory, but even the sparse on...

environ 2 mois il y a | 2

Réponse apportée
solving a system of linear equations where A is a 40*40 sparse matrix
I'd suggest that sparse is almost meaningless when the matrix is only 40x40. At that point, the dense solvers are still extremel...

environ 2 mois il y a | 3

Réponse apportée
Putting spaces between elements of a string/
A = ['011001110000';'101111000000';'110100011000';'011010001100';'010101000110';'110010100010';... '100001010011';'10100010...

2 mois il y a | 2

| A accepté

Réponse apportée
How to download the certificate
I'm sorry, but no, we cannot resolve your problem. Answers is not customer support. Answers is a volunteer forum, generally comp...

3 mois il y a | 0

A soumis


HPF - a big decimal class
High precision floating point arithmetic, a new class written in MATLAB

3 mois il y a | 8 téléchargements |

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Réponse apportée
Defining inequality constraint A*x <= b for genetic algorithm
As I said in my comment, you cannot set up a linear system of inequalities to constrain that curved path from self intersections...

3 mois il y a | 0

Réponse apportée
i want to add cplex and yalmip on my mac how ?
YALMIP is an external toolbox, written in MATLAB, so it could in theory be used by any MATLAB installation. However, it is proba...

3 mois il y a | 0

| A accepté

Réponse apportée
flag a question as answered.
While DGM gave a very complete answer, worthy of acceptance in my eyes, I think, from a look at one of the other questions from ...

3 mois il y a | 1

Réponse apportée
Finite elements model using STABIL
I cannot test your code, as I lack the tools you are using. Regardless, IF you tell us the solve yields NaNs, then there are onl...

3 mois il y a | 0

Réponse apportée
Using logic to select specific values in a matrix
Well, you are doomed to failure, as long as you don't use the right variable names as you created them! A = [1, 0.1234 1,...

4 mois il y a | 0

Réponse apportée
In how many functions using the global variable, can a global variable be declared?
There is no limit on how many functions can use a global variable. At the same time, I will plead, for your own sanity, to recon...

4 mois il y a | 1

Réponse apportée
How do I plot a graph with the grid for trig functions with 0 ≤ x ≤ 2π
@Sean syms x f = cos(x) dfdx = diff(f) help fplot

4 mois il y a | 0

| A accepté

Réponse apportée
Should I need keep in my PC previous versions of Matlab?
Some of us keep older releases, just to answer a question about an older release, testing out code in the old release. I do ten...

4 mois il y a | 0

Réponse apportée
Unable to fetch more decimal points for values stored in sldd
You need to learn about the format command. All of the digits are still there, they were just not reported. I'll add a few digit...

5 mois il y a | 1

Réponse apportée
The symbol "1" is not a scalar in integral3
If ALL you want to do is compute a volume, especially of such a simple domain, there are better ways to do so. If the domain is ...

5 mois il y a | 1

Réponse apportée
How does the svd function determine or fix the phase of singular vectors?
First, signs are to some extent arbitrary. That is, for EIG, you can multiply an eigenvector by -1, and it is still an eigenvect...

5 mois il y a | 1

Réponse apportée
Obtaining the differential equations from graphical representation of the problem
Can you show that a set of equations is a valid representation of some data, merely by comparing them to a curve you find in som...

5 mois il y a | 0

| A accepté

Réponse apportée
Will the old-style class definitions be supported in future version of Matlab?
One thing you cannot realistically ask on Answers (if you expect a fully valid answer) is what decisions about MATLAB will be ma...

5 mois il y a | 1

Réponse apportée
Modelling a system of differential equations with recurrences in matlab
This is known as a delay differential equation. You will find any solvers for them starting with the letters dde. help dde23 Y...

5 mois il y a | 0

Discussion


OH NO! isprime is missing? (Just kidding)
What if you had no isprime utility to rely on in MATLAB? How would you identify a number as prime? An easy answer might be some...

5 mois il y a | 0

Réponse apportée
Iterating the eigenvalue function (eig) produces patterns --- is this a well known result?
I'd have a hard time believing this is well known. @Christine Tobler would be the one to know though, and she agrees. It just f...

5 mois il y a | 0

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