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John D'Errico


Retired

11255 total contributions since 2004

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
optimum conditions - fitlm
No, you have not depicted any curve or surface. You may think you attached something, but you did not. Do you see anything attac...

12 hours ago | 0

Answered
Can I use the minimax optimization algorithm for multiple variables?
If your goal is to set thresholds which are then used to group your data into subgroups, the answer is no. Sorry. Why? Think ...

17 hours ago | 0

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how do i explain which eigenvector the software reports as there are theoretically an infinite number?
Return to linear algebra 101. Do not pass go, do not collect $200. Really, if you will be using tools like eig, it would be good...

18 hours ago | 0

Answered
Why am I getting images that are less exposed than they should be based on my settings?
I will bet that when you set everything to manual mode, you get a raw image, as it comes directly from the sensor. When you let ...

20 hours ago | 0

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Is there a simple way to rotate a matrix 45 degrees? (like rot90)
No. Your plan completely fails for 2x2 matrices, or for any even size matrix at all. As well, it also fails for matrices larger ...

20 hours ago | 1

Answered
matlab code erro massage where ~ used
The problem is you took some code for a newer MATLAB release than you have. So the answer is to get a more recent version of MAT...

1 day ago | 0

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det(x) is non zero
It is time for you to learn what are floating point numbers. Also, why det is a dangerous thing to use in general. det is com...

3 days ago | 1

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How to access zero index in the following code?
Do you mean that you cannot use an if test? It is not possible to test for when i==1, and use a slightly different formula? Hmm....

3 days ago | 0

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Answered
Sine Regression with NonLinearModel.fit
You are making the mistake of providing poor starting values. You simply needed to provide a set of more intelligent starting va...

3 days ago | 0

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Answered
Optimization problem with 2 unknowns
In terms of the optimization, you don't have TWO variables. You have two unknown matrices, containing 933*2488+933*933 total unk...

4 days ago | 0

Answered
How can I find the mixed partial derivatives using Matlab?
You would differentiate with respect to y twice, so the second derivative, and once with respect to x. Essentially two calls to ...

5 days ago | 0

Answered
Hi, everyone i have an array of 500 random values i want to plot a pdf from this kindly help me. I am uploading array file.
help hist Though, it will probably be rather a waste of time. hist(T_Ag,100) <</matlabcentral/answers/uploaded_file...

5 days ago | 0

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Answered
how i can return the index of an array?
Time to read the manual, given a basic problem. Either of these tools will do what you want: help find help ismember

5 days ago | 1

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Answered
Calculate t maximums in single vector
Sort them. Then take the first 5 elements from the sort. WTP? No. It is not ONE single command. Not an option. Of course, not...

5 days ago | 0

Answered
solving trigonometrique equation ?
You will never get an analytical result here. vpasolve(g1) ans = -0.04489097131344154920928045475445

5 days ago | 0

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Why I get different results evaluating the same matrix usign the symbolic toolbox and the numerical approach?
Simple. Because the symbolic TB uses higher precision arithmetic than does double. On some problems this matters. As well, the s...

6 days ago | 0

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How can I plot a correct fft of cosine wave?
What did you plot? Hint: look at the code you wrote: k=0:fs:11*fs; stem(k,y) What is plotted as the x axis? The numbe...

6 days ago | 0

Answered
Curve fitting: Difference fit, nlinfit, fitlnm
The differences are simple. These tools mainly come from different toolboxes. That is really the main difference. Curve fitting ...

6 days ago | 0

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Answered
Curve fitting: What does LAR do?
I don't understand what is confusing. The sum of the absolute values of the residuals is clearly NOT least squares, thus a minim...

6 days ago | 1

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Answered
how can I get matlab/simulink contain thermodynamics libraly?
Start writing. Nobody can give you code from toolboxes that you do not own. Or upgrade your copy of MATLAB (and the correspon...

7 days ago | 0

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Undefined function or variable f when using solve function
Did you ever tell MATLAB in advance that f is a symbolic variable? help syms

7 days ago | 0

Answered
Measure whether two curves are significantly different from each other
I'll argue that you cannot assign any statistical significance to the difference between two sets of points as curves, when you ...

7 days ago | 0

Answered
Command "cluster" with big data: it used to work fast but now it works slow
Since we have absolutely nothing to go on about the actual data, I can only guess. Clustering tools usually use random starts...

7 days ago | 0

Answered
Generalized Linear Regression to Find Heat Capacity
help polyfit

8 days ago | 0

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Is there a quick way to calculate rank of a binary sequence?
For any vector of length N, most of the matrices you would try to form are not even validly rectangular matrices. Thus for a vec...

8 days ago | 0

Answered
Why does it take forever to solve my optimization problem (using ode45 and fmincon)?
How can we know what you did that now causes the problem? Since we do not see your code, we cannot read your mind. You changed s...

9 days ago | 0

Answered
Question about a Logistic Equation
You are correct that Nrab is the problem. You need to learn about the element-wise operations, {.* ./ .^} , all designed to hand...

9 days ago | 0

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Answered
Is there a way to manually input an objective function value to find the next iteration x values?
What do you mean that it is built into MATLAB? No, PSO tools are NOT part of MATLAB proper. There are PSO toolboxes you can down...

10 days ago | 0

Answered
converting .001 .002 file
Get a list of all the files. dir will do that. help dir Then, rename each file, using a loop over the files. Just create...

10 days ago | 0

Answered
Problem with polyfit and polyval
You start off doing a bad thing in these two lines:. GFit = polyfit(Freq,G,length(Freq)); PhaseFit = polyfit(Freq,Phase,...

11 days ago | 1

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