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John D'Errico


Retired

4,609 2006 이후 총 참여 횟수

Mainly retired from Eastman Kodak. (Of course, Kodak itself is now semi-retired. I don't think I had any influence in that.) I still write MATLAB code as I find something interesting, and I do attempt to write new tools to put on the File Exchange when I think I can make a contribution.

However, I DON'T answer direct e-mail questions, and I do NOT do homework. In general, your homework is YOUR problem, not mine. Please do NOT e-mail me with your homework problems or student projects. If I was willing to answer your questions, I would very rapidly become overwhelmed, because one question is never just one simple question.

When I'm not doing something with MATLAB, you might find me playing bridge, either in the club or online on BBO.

Professional Interests: MATLAB, numerical analysis, mathematical modeling

Avocational interests: Bridge, woodworking, woodturning

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답변 있음
A problem that the Ode45 solver did not finish the computations
The answer is (probably) simple. I need point out only a couple of lines of your code that tells me it is so. (In fact, I was al...

약 7시간 전 | 0

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How to use questdlg to ask the user for an action?
Your first problem is you are not using it correctly. The last argument should be one of the choices, to give it a default butt...

1일 전 | 0

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Using a tolerance in X with fzero function (by default the tolerance is evaluated on Y axis).
Actually, if you check the docs for fzero, you will find it uses exactly 5 of the possible options properties - Display, FunValC...

2일 전 | 0

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When using polarplot, why does the argument come before the modulus?
There is no officiially agreed convention, nor can there really be one. Don't expect the author to have used the same convention...

2일 전 | 1

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Problems with fmincon for design optimization
Jeff Miller told you this, the first time you asked this question. I'll repeat it, since you don't seem to believe him. You CAN...

3일 전 | 1

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Solving a 2nd order ODE
It is arguably bad notation to have x0 and x_0 as two variables that mean very different things. Confusing as hell, and if you d...

3일 전 | 2

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Fit data to sawtooth shape
Too late for an answer for Angela, since I never saw the question a year ago. But a simple model for such a curve will not be to...

4일 전 | 0

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How to perform norm on each row of a matrix?
What is a norm? I assume by norm, you mean the common Euclidean norm, thus the 2-norm. (Other norms will be just as easy for the...

4일 전 | 0

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답변 있음
Randi worked in a program I ran 5 weeks ago, today it doesn't-what gives?
Don't write an m-file that is named randi, at least, if you will ever want to use randi. Try this: which randi -all If there i...

4일 전 | 1

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Finding Complex root for the nonlinear equation with single variable
Please don't answer your question with a comment. But the answer is, not you cannot use fzero to find a complex root. fzero ONL...

5일 전 | 0

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How to interpolate over long section of bad data?
I had to laugh. No, your problem is not how you defined xq, but more in how you defined x! At least you were thinking in sort of...

5일 전 | 0

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Some insight on mvnrnd function
For once, someone asks a good question, that says they saw something they did not understand, and want to understand what happen...

5일 전 | 2

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답변 있음
Non-reproducible solution with non-linear fitting
Do you understand that when you do not specify astart point, that fit uses a RANDOM start point? So why would you expect the sam...

5일 전 | 0

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What is the best way to store different variables into 1 variable?
Use a cell array. Or use a srruct. Either can store anything you put into it. Here, a struct will allow you to store everything...

6일 전 | 0

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Solving system of inequalities and plot in 3-dimensional
Um, just because you have decided that the solution is what you plotted there, does not make it consistent with the set of inequ...

7일 전 | 0

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array indices must be positive integers or logical values.
p is sometimes zero. sometimes it is one. how you are creating p is a bit silly, as there is absolutely no reason to use bin2dec...

7일 전 | 0

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답변 있음
Problem with the optimization of the Economic MPC
Simple. Your objective function is essenitally constant around the start point, or you provided a start point that actually hap...

8일 전 | 0

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Convert a tetrahedron mesh to triangular mesh or surface mesh.
Easy. Assume that tess is an nx4 array, composed of references into the set of vertices. Then surely is it true that: facets =...

8일 전 | 1

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the inverse of spapi function
I think this may be what you are asking for. x = 1:7; y = rand(1,7); S = spapi(5,x,y) S = struct with fields: ...

8일 전 | 0

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How to find the first n postive roots of a function?
You can't do so. Well, not perfectly. Why not? Because I can always provide a function that has roots that are impossible to fin...

8일 전 | 0

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46Go on my hardrive ?
It strongly depends on how may toolboxes there are in the two installations. It may also be a function of release, if they are d...

9일 전 | 0

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Why my eigenvalues from (v,d)=eig(k,m) are so close to each other?
You will have 9000 eigenvalues. Some will be small, some larger. How far apart do you think those that are small can realistical...

9일 전 | 0

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numbers and characters in same vector
Store them in a cell array, actually a cell vector. help cell Index a cell array using curly braces, instead of parens. Thus {...

9일 전 | 1

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Runge Kutta method computational cost
tic and toc are really bad ways to estimate the time required for (almost) anything, unless the time is pretty long, and you onl...

10일 전 | 2

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Polynomial Fitting of 3 variables
Download polyfitn from the file exchange, here: https://www.mathworks.com/matlabcentral/fileexchange/34765-polyfitn Ensure you...

10일 전 | 0

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Multiple equations using a range of inputs for one variable then plotting a graph.
Sorry, but your question makes no sense, at least not at first glance. If you want help, then clearly explain what you are doing...

10일 전 | 0

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How do I determine goodness of the fit (any curve )when using least square method?
There are many measures of goodness of fit for a least squares problem. NONE of them are perfect. As well, there are entire grad...

11일 전 | 0

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how to sum data with condition
Sorry, but it is a really bad idea to have separate functions for each case. Just pass in the the first column element as an ar...

12일 전 | 0

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How to calculate displacement from acceleration data?
You already know how to use trapz. Just use it twice. However, you mention instantaneous displacement, and the problem with trap...

12일 전 | 0

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I need to have underline (_) in my plot x and y label but matlab plot recognizes as subscript
They can't win. Some people want to have subscripts. Some want an actual underscore character. Nobody is ever happy. xlabel 'x\...

13일 전 | 1

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