John D'Errico

Last seen: Today | Aktiv seit 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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Can I solve a symetric system using only the lower triangular portion of the matrix?
You don't show your matrix. Only a picture of it, and a picture is not quite worth a thousand words all of the time. ;-) But co...

ein Tag vor | 0

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free trail doubt issue
After it ends in 30 days, it will just end. You will have a choice then of continuing your use of MATLAB by paying the normal fe...

6 Tage vor | 0

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Volume and Surface Area of a Compound Geometric Object
First, alpha shapes tend to be poor at representing volumes with sharp internal corners, like those between the intersection of ...

9 Tage vor | 1

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Call parameters by their variable name in Simulink rather than having to index the value.
If you can pass in a vector, then you can pass in a structure. Just assign fields to the structure. parameters.khch = 2; There...

10 Tage vor | 0

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looking for creator of specific code
The codes I did find were a bit more sophisticated in general, and I did not expect to find anything. HOWEVER, when I looked on ...

10 Tage vor | 1

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¿Cómo podría solucionar matrices por el comando [L,U]? no sé nada respecto al tema
I think your confusion stems from a misunderstanding. LU is fine, even with rank deficient matrices. As long as you use the MATL...

14 Tage vor | 0

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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...

26 Tage vor | 1

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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...

etwa ein Monat vor | 0

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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...

etwa ein Monat vor | 0

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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...

etwa 2 Monate vor | 0

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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 ...

etwa 2 Monate vor | 0

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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...

2 Monate vor | 0

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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...

2 Monate vor | 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...

2 Monate vor | 0

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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...

3 Monate vor | 1

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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...

3 Monate vor | 1

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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...

3 Monate vor | 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...

3 Monate vor | 0

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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...

3 Monate vor | 0

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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 Monate vor | 0

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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...

4 Monate vor | 0

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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...

4 Monate vor | 0

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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...

4 Monate vor | 1

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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 Monate vor | 0

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**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 Monate vor | 1

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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...

5 Monate vor | 0

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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...

5 Monate vor | 2

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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...

5 Monate vor | 0

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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...

5 Monate vor | 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...

5 Monate vor | 3

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