John D'Errico

Last seen: Today | Active since 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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Answered
Can we simulate a material suddenly becoming unstable in MATLAB ?
This is probably closer to a thesis level question in mechanical engineeering than one for Answers, at least, depending on how d...

6 hours ago | 0

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Answered
Find x from y using a fit equation?
The simple and fully general solution is to use fzero. For example... x = rand(20,1); y = 2*x + 3 + randn(size(x))/5; plot(x,...

7 days ago | 1

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Answered
Find angle from equation has sin(theta)/theta
Note that there is no analytical solution to a problem with sin(theta)/theta. This is as opposed to the very similar looking for...

10 days ago | 0

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Error while outputting graph
I'm pretty sure you want to substitute in different values of the undetermined constants, then plot each corresponding curve, bu...

1 month ago | 0

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Does anyone know why no matter what I change, I cant get dsolve to work?
I dropped out some of the stuff you did that was unnecessary. For example, the first line creates y(t), and implicitly also defi...

1 month ago | 0

Answered
What is the ECCN of Matlab 2014
I would argue that any release of MATLAB will live under the same ECCN. The wording in no way applies only to the current releas...

2 months ago | 0

Answered
Lake America used as a name in Mapping Toolbox
I know enough people at MathWorks to believe they will not be bullied into such a stupid thing. Ok, I hope not, trusting in the ...

2 months ago | 1

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Answered
Nonlinear Newton solver fails near resonance for porous moonpool model
Um, so what should we do? First, Newton's method is generally a great scheme. (You even understand that aspect from what I read ...

2 months ago | 0

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How to multiple very large numbers in Matlab?
Remember that Excel, just like MATLAB, is representing those numbers in a double precision form, and that limits you to roughly ...

2 months ago | 0

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Histogram gives a wrong result？
Never assume that two mathematically identical floating point numbers will, if computed using different expressions, produce the...

2 months ago | 0

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Please help me determine positive values of s and h(s,h>0) such that L1 and L2 have opposite signs. Then print L1 and L2
What have you tried? Look carefully at what you have. Take it apart, one piece at a time. a1=0.2494; a2=0.75; a3=0.01; a12=1.69...

3 months ago | 0

Answered
What exactly does ε represent in numerical computing
Just to add some more info... For example, pi(x) is known as the prime counting function to some, the number of primes less tha...

3 months ago | 0

Answered
Why does parfor slow down with large shared arrays?
I can't test this myself, and I lack a great understanding of the parallel tools. But it looks like there are a few issues, main...

3 months ago | 0

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How to get abbreviations into vars?
Can you just exclude a term just by looking at it, without knowing the parameters in it? Given the complexity of the mess you ha...

3 months ago | 0

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Why is vecnorm So Slow?
The jump is often a question of algorithm changes. You would be surprised how often algorithms exhibit nonlinear breaks. As I re...

3 months ago | 1

Answered
HDL coder support for Microchip high level synthesis tool SmartHLS
I'm sorry, but Answers is not a team. And we have no access to any information about timelines or any knowledge of when a given ...

4 months ago | 0

Answered
why does factor(1) return 1? shouldn't it return null?
Yes, I agree, in that f1 = factor(1) could arguably return empty. 1 is not indeed prime, and so the result is inconsistent wit...

4 months ago | 0

Answered
solve() returning empty, does a solution exist?
Just because solve returns empty does not mean a solution does not exist. In fact, most relations you can write down have absolu...

4 months ago | 1

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Answered
Saving my path for future sessions.
The trick here is to use the help, because it teaches you what to use, at least it gives you a hint at how to solve it. If you m...

4 months ago | 0

Answered
Help using the toeplitz function
20x20 is not large by any measure I would ever imagine. 20000x20000 might be large. :) Of course, large is a purely subjective a...

4 months ago | 0

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Answered
MATLAB Randomly Changes Values in Array to Scientific Notation
It is literally a certainty that some of those values are only approximately integer. No question in my mind. And is certainly n...

4 months ago | 0

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Answered
How to call kummerU for a stand alone program
You cannot do it from MATLAB, as stated by others. However, it looks like python does offer similar functionality. And I believe...

4 months ago | 0

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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...

5 months ago | 0

Answered
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...

5 months ago | 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 ...

5 months ago | 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...

5 months ago | 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 ...

5 months ago | 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...

5 months ago | 0

Answered
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...

5 months ago | 1

Answered
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...

6 months ago | 0

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