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John D'Errico


Retired

4.407 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
Create block sparse matrix
Are you asking how to create a block diagonal sparse matrix? Easy peasy. tic N = 100; M = 10000; Z = sparse(rand(N,N*M)); ...

ongeveer 8 uur ago | 0

Answered
How to generate a random point in the volume of a cylinder
Since you already have an answer posted... Pretty easy, actually. So two points that define the ends of the cylinder, and a know...

ongeveer 10 uur ago | 0

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Answered
can we check a condition at the end of a loop?
Where you are struggling is in explaining what you want to do. Giving an example is often a good idea. That is, give an example ...

3 dagen ago | 1

Answered
Trying to do an integral
An alternative is to try a different solver. I seems Alpha finds a solution for the indefinite integral, so the definite integra...

4 dagen ago | 0

Answered
When using alpha shape and the alpha radius is not specified. How does MATLAB obtain it? I want to understand it.
I don't have access to the code, so I can only surmise (since I've written alpha shape codes before in MATLAB, but not the one i...

5 dagen ago | 0

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Answered
intermediate exponential calculation goes to infinity
Calc 101. An integral is a linear operator. You can move any multiplicative constant inside or outside of the integral. Suppos...

5 dagen ago | 0

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Answered
Generate beta random number without statistics toolbox
As a followup, I note that the answer by dpb seems to be incorrect. There are several ways to generate a beta random variable. ...

6 dagen ago | 0

Answered
Symbolic solver yields wrong solution
It seems a subtle thing. We need to "branch" out from our preconceptions. ;-) pretty(solutions) / 0 \ | | | -p ...

7 dagen ago | 4

Answered
How do I explain the random functions to my professor?
I wonder if your professor needs to learn a few things. For starters, that Minitab is not doing anything any better than is MATL...

7 dagen ago | 5

| accepted

Answered
How to fit a curve to a step function?
ALWAYS plot everything. Do that before you do anything else. plot(xavg_40s1,havg_40s1,'.') grid on So your data looks like ...

8 dagen ago | 3

| accepted

Answered
Not enough input arguments
What is the purpose of that line? Lets see... help square 'square' requires Signal Processing Toolbox. So, assuming that you ...

8 dagen ago | 0

Answered
NAN from griddata for scatteredInterpolant
Your problem is that you have no idea how to use those tools. There is no need to use griddata AFTER you used scatteredInterpola...

8 dagen ago | 0

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Answered
Graphing two parametric functions in terms of x
You got exactly the correct thing. You just need to look carefully at the y axis labels on the two plots. Just add this line af...

8 dagen ago | 0

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Answered
Are there any plans to add support in exportONNXNetwork tool for the maxUnpooling2dLayer?
Sorry, but surely not possible to tell you. MathWorks does not discuss their plans for the future on this forum. Anyone who doe...

8 dagen ago | 0

Answered
creating a curve from XYZ points (centreline) and then split curve into new points
This is a simple problem of interpolation, except that you don't know how to do the interpolation. Standard tools like interp1 d...

9 dagen ago | 1

Answered
Matlab Crushes when new .m file is added
This is not a crash, nor even a crush. It is just that MATLAB caches the files in the MATLAB directories. It does this to enhanc...

9 dagen ago | 0

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Answered
dot product for complex vector
help dot dot Vector dot product. C = dot(A,B) returns the scalar product of the vectors A and B. A and B must be ve...

9 dagen ago | 0

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Answered
i need to switch all integers in my array to positive numbers
You might need to read the getting started tutorials, if you are asking questions this basic. help abs

9 dagen ago | 0

Answered
large numbers in K means
x = rand(1048575,1); size(x) ans = 1048575 1 [IDX, C] = kmeans(x, 10); C Warning: Failed to converge...

9 dagen ago | 0

Answered
Expression of interpolating function
A high order interpolating polynomial is a REALLY, REALLY, REALLY bad idea. There, if i said it three times, it must be true. Se...

9 dagen ago | 0

Answered
In-Situ Combustion Model - MATLAB code
This is a simple error of syntax, which seems a bit strange for someone who has written such a long code to misunderstand. You s...

10 dagen ago | 1

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Answered
H is a 108x108 tall array, P is a 108x9 double array, when excute etu=H\P , this syntax is wrong, what is right ?
Why would you use tall on a problem that tiny? Anyway, you could just convert to double. In fact, that proves you do not seem to...

11 dagen ago | 0

Answered
Generate Random Matrix 0's,1's
Easy enough. matno = 10; % the number of random possiblities rows=10; columns=3; Now we want to create a matrix of size (row...

11 dagen ago | 1

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Answered
if i used a free trial will my files save
Yes.

12 dagen ago | 0

Answered
How do I extract 3D matrix from 5D matrix
What does it mean to extract a specific matrix? p = 1; z = 1; A = D(:,:,:,p,z); is a matrix of the desired size, extracting...

13 dagen ago | 2

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Answered
Sparse Matrix with Non-positive Indices
What you say makes no sense. If you have a full matrix already, and you are turning that into a sparse matrix, then you would ju...

14 dagen ago | 1

Answered
Problem optimizing anonymous function using fzero
There is no need to use symbolic tools to solve problems via fzero, merely understanding how to use functions. However, your que...

14 dagen ago | 1

Answered
error using Solve with inequality
You did not follow the example carefully. syms x >> S = solve(x^2 - 4*x + 3 < 0,'returnconditions',true) S = struct with ...

15 dagen ago | 1

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Answered
Obtain eigenvalue from matrix and known eigenvector
The simple answer, as long as the vector x IS an eigenvector. is just: val = norm(A*x)/norm(x); You should see that this is no...

15 dagen ago | 0

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Answered
fsolve doesn't give correct answer even with close initial guess
A serious issue is that you use many numbers accurate to only 2 decimal digits. So even though you may think the answer is corre...

15 dagen ago | 0

| accepted

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