John D'Errico

Last seen: Today | Attivo dal 2006

Followers: 41 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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Convergence error in numerical method.
99,9% probable user error, 0.1%, it could be real. Hey we cannot know, since we don't see your code. But the point is, you hav...

7 giorni fa | 1

Risposto
Minimally constraining an FEA Model in Matlab
If it is resting on a surface, it is not resting gently, in the sense that it CANNOT freely expand below the surface. In fact, y...

18 giorni fa | 0

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Risposto
Find specified number of points on curve with identical chord length (not arc length)
Admittedly, interparc does not solve the problem you want to solve. At least, not the probem you CLAIM you want to solve. As the...

22 giorni fa | 0

Risposto
can this code be improved?
You have asked several questions. 1. Is it well written? 2. Can it be improved? Something you did not ask is if it SHOULD be imp...

circa un mese fa | 0

Risposto
Eigendecomposition not fully utilizing all cores on M1 pro, matlab 2025b
Some operations are not as easily parallelized when utilizing automatic mutithreading. That is possibly the case for eig, where ...

circa un mese fa | 0

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Risposto
I want to decrease the time my Script
If you want to speed up your code, then you need to make the effort. We cannot possibly know what you are doing here, at least n...

circa 2 mesi fa | 0

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Risposto
Why Does polyval Return Zero When the Coefficients are Empty?
(This could easily better belong in a discussion than in Answers.) I could argue that any choice they made was arbitrary, becau...

circa 2 mesi fa | 0

Discussion

Little Fermat, a valuable tool for primality testing
In a previous discussion, https://www.mathworks.com/matlabcentral/discussions/tips/884294-oh-no-isprime-is-missing-just-kidding...

circa 2 mesi fa | 0

Risposto
GA stops with different score every time, even with setting big MaxGeneations and MaxStallGenerations
Nonlinear solvers, of which GA is one, cannot be forced to ALWAYS return the optimal result. And while tools like GA are designe...

2 mesi fa | 1

Risposto
Does [V,D] = eig(A) always return normalized eigenvectors for any real matrix A?
Be a little careful that A is not in symbolic form, even if it is real and SPD. A = randn(4,3); A = A'*A % A MUST clearly be SP...

2 mesi fa | 1

Risposto
Is fit() deterministic when StartPoint is specified?
If the start point is specified, then yes, FIT should be deterministic. At that point there is no reason for any pseudo-random n...

2 mesi fa | 2

Discussion

What is an emirp? Can we find a new world record size prime of this form, using only MATLAB, and a home computer?
An emirp is a prime that is prime when viewed in in both directions. They are not too difficult to find at a lower level. For ex...

2 mesi fa | 0

Risposto
fread a double that's been broken up into four 16 bit words
I don't see the problem. For example... Xtest = randn*100 Now, I'll split it into 4 hex numbers, each taking up 16 bits. Xhe...

2 mesi fa | 0

Risposto
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,...

3 mesi fa | 0

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Risposto
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...

3 mesi fa | 0

Risposto
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...

3 mesi fa | 0

Risposto
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...

3 mesi fa | 1

Risposto
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...

4 mesi fa | 0

Risposto
**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...

4 mesi fa | 1

Risposto
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...

4 mesi fa | 0

Risposto
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...

4 mesi fa | 2

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Risposto
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...

4 mesi fa | 0

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Risposto
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...

4 mesi fa | 2

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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...

4 mesi fa | 3

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

4 mesi fa | 2

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Risposto
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...

5 mesi fa | 0

Inviato

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

5 mesi fa | 10 download |

4.9 / 5

Risposto
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...

5 mesi fa | 0

Risposto
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...

5 mesi fa | 0

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Risposto
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 ...

6 mesi fa | 1

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