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John D'Errico


Retired

4,444 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
Reshape: Math lesson help
Your matrix is 5x50. You need to understand how the elements lie in sequence in memory. MATLAB stores each column in sequence. ...

10 hours ago | 0

Answered
spline interpolation image way to connect ?
Your problem is you have a vague idea of what you wanted to do. But you got it completely wrong. Absolutely, completely, so. Yo...

21 hours ago | 2

| accepted

Answered
what is the best method to fit a curve to strain-stress data?
NO polynomial will ever fit that curve (at least, not fit it well.) NONE. PERIOD. x = data_mathwork(:,1); >> y = data_mathwor...

1 day ago | 1

| accepted

Answered
Solving for 4 unknowns
Why do these not look like actual solutions to the equation system? subs(eq1,{L,V,x1,y1},[1.86, 0.29, 0.537, 0.258]) ans = 0 ...

1 day ago | 0

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Answered
64 bit binary number representation in matlab without rounding off
Maybe you are looking for something like this. I wrote a little utility recently that fully extracts the binary form of any nume...

2 days ago | 1

Answered
Why are all the examples for matlab functions hindered by useless simplistic examples that do not show how all features of the functions work? One cannot determine how to use any function of any complexity with the examples given.
As someone who has written dozens of toolboxes, with literally hundreds of functions, and someone who tends to be a manical perf...

3 days ago | 3

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Answered
Fminsearchbnd vs. Pattern Search vs. Surrogate Optimzation to attempt to find the global optimal solution.
Each solver has what is called basins of attraction for each local solution. If you start the solver off in any point in one of ...

4 days ago | 2

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Answered
Random assignments through the use of a MatLab programmed Calender
This is not really a MATLAB question, because it is just programming, something you could do in any language at least in theory....

4 days ago | 0

Answered
sparse matrix operations to gain efficiency
Are those matrices mostly zero? No. It looks like they are 50% zeros. Sparse will not gain anything, because thre is also overhe...

7 days ago | 0

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Answered
How does function std process complex numbers
std uses the formula that is given by David, which is just the standard fornula, with no difference for complex inputs. But just...

8 days ago | 0

Answered
I need help in this question please?
What are you trying to do with the lines: syms B assume(B>1) Which have nothing to do with the problem? It looks like they a...

8 days ago | 2

Answered
how to apply cubic spline interpolation curve fitting
What I think you do not understand is those curves are noisy, and you do not understand splines. The curves you drew are not noi...

9 days ago | 0

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Answered
please explain diag([rand(1,n-2) + 1, 1, 17])
When you have a problem, take it apart from the inside. What is inside-most? Was diag called with multiple inputs at all? (No.) ...

10 days ago | 2

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Answered
How can I calculate the slope of third order polynomial fit
Is there a reason why you would not think to differentiate it? help polyder

11 days ago | 0

Answered
Symbol calculation and numerical values
You are doing things in the wrong order. k,e,m,w are not unknowns. They are knowns. So why have you set them up as symbolic? N...

11 days ago | 0

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Answered
How to construct a weighed 2D histogram?
Just use accumarray to sum the weights in each bin.

11 days ago | 0

Answered
How can I convert red curve in an image into a line ?
What does it mean to convert something into a "curve"? In fact, there is no need to do anything of the sort. You have a picture...

12 days ago | 1

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Answered
Sine curve fit to data with an unknown dc offset
Of course it is possible. Use the curve fitting toolbox. ft = fittype('a + b*sin((x - c)/d)','indep','x'); mdl = fit(X(:),Y(...

13 days ago | 0

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Answered
How can I check if a variable exists within another variable?
It fails, because exist does not apply to fields of a strcture. help isfield isfield True if field is in structure array.

15 days ago | 0

Answered
random numbers without repetition of two consecutive numbers
These things are far easier than you think. In fact, there are (at least) two simple ways to solve it. Generate multiple sets ...

15 days ago | 4

Answered
im not able to run below given code
Now that we know what the problem is, those functions are part of the Phased Array System toolbox. https://www.mathworks.com/he...

16 days ago | 0

Answered
alpha shape vs convex hull volume value
A problem with your data is it has holes in it. The inside looks to be empty. But worse, it has a void on one corner, where the ...

18 days ago | 2

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Answered
Rank of Symbolic Matrix returns incorrectly
"Concuded by inspection." I've gotta laugh at that. B = [ 1, -1, -1, ...

20 days ago | 1

Answered
Interpolating from set of vectors to another with some tolerance?
Confusing as hell. You have one set of values as a pair of vectors, (xfine_i,Tfine_i). As well, you have the same thing at a c...

20 days ago | 0

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Answered
construc matrix D by OD process?
I suppose I'll make this an answer instead of just a comment, since nobody has answered yet. If all you wanted is to construct ...

20 days ago | 1

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Answered
Solving trigonometric equation using "solve" function.
Whats the problem? There is no need to set any properties anyway on such a trivial problem. syms x; x = solve(230.769*cos(x)+1...

21 days ago | 0

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Answered
how to create a symmetric binary variable matrix
You need to learn to index matrices, as you have been posting repeatedly what are virtually the same questions. Fundamentally, w...

23 days ago | 0

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Answered
Display numbers as power of N in a symbolic expression?
I don't think you can, at least, not easily. You can do pretty much anything with sufficient effort of course. syms X expr = e...

24 days ago | 1

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Answered
ode45 varargin - additional arguments after options
Long ago and far away, in an age long since past, MATLAB did not have function handles. There were no anonymous functions. There...

25 days ago | 0

| accepted

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