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John D'Errico


Retired

Last seen: Today Actif depuis 2006

Followers: 1   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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Réponse apportée
scatter command not working
(It is good you are using the tutorials.) But first, learn to read the error message, an important skill in using MATLAB, unless...

1 jour il y a | 1

| A accepté

Réponse apportée
Nonlinear optimization with branching solution space
Just solve 11 distinct problems, each of them continuous. Use a loop, setting x to each of the 11 possible values. Save each sol...

4 jours il y a | 1

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how to create nxn matrix with main diagonal that enters odd rows/columns with zero and even ones start with 2(n+1) sequence
Simple is to use diag. n = 5; % Now many non-zero elements will we have? N = 1:(2*n); % a simple index vector D = N.*mod(N-1,...

4 jours il y a | 0

Réponse apportée
Does I properly translate the equations in matlab code?
Ouch. That would be a miserable set of equations to try to code. (You have my sympathies.) I did some very quick spot checks, an...

4 jours il y a | 0

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problem in curve fitting
C1 continuous? Is there a difference? Absolutely YES. C1 continuity, using circular "arcs" in 3-d? UGH. I'm a career mathemati...

5 jours il y a | 0

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species go to negative values
Remember that the software does not truly understand your model, and what you are attempting to simulate in that model. It only ...

5 jours il y a | 0

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Better "probabilities"?
How effective is rand? I'm not sure what you mean by "effective", or for that matter, "advanced". It is a state of the art rando...

6 jours il y a | 1

Réponse apportée
Need help solving heat equation using adi method
You say it works for sufficiently small values dt. With that exp(t) term in there, do you seriously expect it to work well for...

7 jours il y a | 0

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Non-linear Algebraic 36 equations unsloved
Actually, a starting value set like ones(36,1) is often a dangerous thing to do. Making all of the starting values the same can ...

8 jours il y a | 0

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math model of neural network fitting
As is often the case with such "models", there is nothing you could write down, at least not easily, and without nasty arrays of...

8 jours il y a | 0

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About Fluid dynamics in a porous medium...
As @Torsten said, this is far too vague a question. I would suggest starting with a far simpler problem, especiially good is if...

9 jours il y a | 0

| A accepté

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inversing huge Y Matrix
As always, I'll start by saying that computing the inverse of a matrix is a bad idea. And of course, you don't say what you thin...

9 jours il y a | 0

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How can I solve this implicit function in MatLab?
Trivial, in some eyes. ;-) This is one of the simpler implicit problems you might write down, since a direct solution exists in ...

9 jours il y a | 1

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How to add unknow parameter in matrix and solve it by use det() syntax for finding w
syms w; m1 = 1.8; m2 = 6.3; m3 = 5.4; m4 = 22.5; m5 = 54; c2 = 10000; c3 = 500; c4 = 1500; c5 = 1100; k2 = 1*10^8; k3...

10 jours il y a | 0

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solving linear systems of equations
A long forgotten question and one with an answer that may not be appreciated by @Chloe St John, given that multiple questions by...

11 jours il y a | 0

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MathWorks Administrator Account Privileges
Contact customer support at MathWorks. That is not Answers. We cannot help you directly. https://www.mathworks.com/support/cont...

11 jours il y a | 0

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When integrating acceleration do you need to convert velocity?
When you keep on subtracting off the mean, you do strange things to the result. But you need to consider what a constant of inte...

12 jours il y a | 0

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How to efficiently solve a system with an infinity number of solutions?
Note that a solution need not always exist for all n. When n==1, and so A is a 1x1 matrix, it is completely known. So unless yo...

12 jours il y a | 0

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How can I calculate the integral of Legendre function P(n,theta) ?
@Shreen El-Sapa I think you do not understand that a Legendre polynomial is meaningless over some other interval. It has no spe...

13 jours il y a | 1

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Create a matrix and a map of Hydrologic Soil Group values using integer or character values
MATLAB does indeed allow you to produce a character matrix, with those characters. However, I assume you have scattered data, wi...

14 jours il y a | 0

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Determine row vector out of matrix with most evenly spaced and distributed values
Simple. Sort of. But you need to define what equal spacing means to you, and how you will measure the deviation from equal spaci...

14 jours il y a | 0

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Réponse apportée
Are polyshape vertices preserved reliably without floating point errors?
Um, probably, yes. But potentially no. Yes, because on most operations, you will just be indexing into the original set of vert...

15 jours il y a | 1

Réponse apportée
Integrate function by for loop
As always look carefully at your code. Learn to use the debugger. It would tell you the problem, and in which line there was a p...

15 jours il y a | 0

Réponse apportée
matrix, where each element is a column vector
You don't need a cell array at all! Just use a 3-d array. A = randn(11,7,1001); Now to compute the max in each vector, just u...

15 jours il y a | 1

Réponse apportée
inverser la matrice tri-diagonale
As much as I hate the suggestion, you could trivially use inv. ;-) Better would be to use sparse matrices. That is, learn to us...

15 jours il y a | 0

Réponse apportée
Solve long matrices equation
This is a classic algebraic Ricatti equation. https://en.wikipedia.org/wiki/Algebraic_Riccati_equation How do you solve it in ...

15 jours il y a | 0

Réponse apportée
fminsearch doesn't converge to the right value
These things are always easier than you think. Well, except when they are just as hard as you think. ;-) First, I'll create x a...

16 jours il y a | 1

| A accepté

Réponse apportée
How to use a variable from script in a function that is in another script
Just create your function like this. In my example, k3 and m3 will be assigned, so that you can see how it works. k3 = 3; m3 =...

17 jours il y a | 0

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How do I lower an image quality?
There are other ways to lower image quality. Several ideas have already been mentioned. Resize the image, then expand it back u...

17 jours il y a | 1

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I am struggling trying to figure out this code I have it completed but I keep getting errors, can you help?
I need to laugh (sorry, but it is true) every time I see someone claim they have completely written a long piece of code, and cl...

18 jours il y a | 0

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