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John D'Errico


Retired

4,591 total contributions since 2006

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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Answered
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: ...

8 hours ago | 0

Answered
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...

15 hours ago | 0

Answered
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...

1 day ago | 0

Answered
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...

1 day ago | 0

Answered
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 {...

1 day ago | 1

Answered
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...

2 days ago | 2

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

2 days ago | 0

Answered
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...

3 days ago | 0

Answered
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...

3 days ago | 0

Answered
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...

4 days ago | 0

Answered
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...

4 days ago | 0

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Answered
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\...

5 days ago | 1

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Answered
How can I construct delauany's disc in matlab??
Hmm, if that was what you were expecting, you did not come very close. :) Let me suggest a trick though. Write a little helper...

6 days ago | 0

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Answered
fibonacci series, while loop
Well, what is important to me is you have made a credible effort, and gotten close. In fact, you did compute Fibonacci sequence ...

7 days ago | 0

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Answered
Estimating precision of matlabs matrix solver
The precision? Double precision. It works in double precision. But that is not your real question. The issue is how good are the...

8 days ago | 0

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Answered
Help with Writing Function Files for Nonlinear Functions
Suppose you tried to use the MATLAB function mean. It takes at least one argument. What would happen, if you just tried typing m...

8 days ago | 0

Answered
Generate Random Number inside a closed area
Not hard. But it takes a little effort. (I should post a tool for this on the FEX. SIGH. Actually, I have a tool that does this,...

8 days ago | 1

Answered
What starting point to choose so fsolve always returns a solution when any exists?
I tend to describe tools like fsolve with a metaphor of a blind man set down on the surface of the earth, then tasked with findi...

9 days ago | 1

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Answered
How to use DWT for denoising complex data like OFDM symbol ?
So why not just denoise the real and imaginary parts separately, then combine them back into one complex array. Two calls instea...

10 days ago | 0

Answered
icdf versus erfinv?
In general, use the ICDF code! Why would it be more accurate? Because it can be more intelligent, using a more accurate approxi...

10 days ago | 1

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Answered
how do I calculate pi
Easy. Type pi at the command line. Works like a charm. Harder, since you did make a very credible effort at a solution, first, ...

10 days ago | 0

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Answered
how to set initial guesses in Curve fitting to avoid the local minimum?
As Alex says, it is not easy, and no perfect answer exists. The model you have posed is a difficult one to estimate, because i...

10 days ago | 1

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Answered
How to multiply the different values of same variables
And the problem is? P = 1; for i = 1:Imdone x = (stuff) P = P*x; end

10 days ago | 0

Answered
Rearrange randomly just some parts of an array
I fail to see the problem, although you are the only one who knows the rules that created this vector, so you will know what to ...

10 days ago | 0

Answered
How to generate a vector with specific values (maybe using loops)?
Don't. Instead, use arrays to store them. n = 4; V = eye(n); V V = 1 0 0 0 0 1 0 0 ...

11 days ago | 0

Answered
Defining non-coefficient constant in fittype
While this is trivial to solve using the CFTB (that is, fit) it is even simpler to solve using backslash. Assume that omega1 an...

12 days ago | 0

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Answered
How to write log base e in MATLAB?
The log function does exactly what you want. log(14 - y) If you want a base 10 log, you use log10. There is also a log2 functi...

12 days ago | 2

Answered
Precision in calculation of large digits
What you need to understand is how MATLAB works. When you have one function call another, it evaluates the inside operation FIRS...

12 days ago | 2

Answered
Multiplying every secound element in a vector with -1
You need to start learning MATLAB. That is, actually learn to use vectors, matrices, not just work with single numbers, and loop...

13 days ago | 1

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Answered
Surf plots 2D + color. I want a 3D plot. What is the solution?
But what you have, that is z(x,y), is a 2-dimensional manifold in R^3, that is, a surface embedded in the 3-dimensional cartesia...

13 days ago | 1

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