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John D'Errico


Retired

4,393 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
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...

8 hours 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...

12 hours ago | 0

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...

20 hours ago | 0

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

1 day 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...

1 day 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...

1 day 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...

1 day ago | 1

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...

3 days 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...

3 days ago | 1

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

4 days 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...

4 days 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...

5 days 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...

6 days 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 ...

6 days 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...

7 days ago | 0

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...

7 days ago | 0

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Answered
nonlinear curve fitting a function on data
sin(theta) is not a variable name. beta = 1.135e-4; sintheta = [-0.81704 -0.67649 -0.83137 -0.73468 -0.66744 -0.43602 0.45368 ...

7 days ago | 1

| accepted

Answered
I have 30x30 matrix and need to extrapolate lower triangle numbers
You just want to extract the lower triangle, whatever is in it? The result going into a vector? A = magic(5) - 10 A = 7 ...

9 days ago | 0

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Answered
Solve for a system of equations
This is not actually a question about MATLAB. Why would you assume that every set of complicated nonlinear equations has an exp...

10 days ago | 0

Answered
Matrix Division: Different sized matrices
Is there a reason why you have not read the getting started tutorials? The manual is always a good thing to read. C = A./B; ...

10 days ago | 2

Answered
How do I find what y equals from an equation?
First, when you have a question about an error, report the entire error, that which is written in red in the command window. Wh...

10 days ago | 1

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Answered
Why does this code output all values as 1?
A significant problem with your code is in your assumption that this line does what you rthink it does: elseif r1<=r(i)<=r2 I...

10 days ago | 0

Answered
If first and last rows of an orthogonal matrix is known, is it possible to determine remaining orthogonal rows?
If this is homework, and you need to do this using tools other than null, sorry, you are out of luck. I won't do your homework. ...

10 days ago | 0

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Answered
Calculating Percentile from a pdf
Pretty simple actually, though it is far easier as I can give you an example, than if you posted your actual data rather than a ...

11 days ago | 0

Answered
how to work with symmetric image
Sorry, but this is completely underdetermined. You can never recover A1, from the composite C. Consider any arbitrary array A1....

11 days ago | 0

Answered
How can I make a Spinal Cord using matlab 2013?
Yes, surely so. Anything can be done. For that to happen, you will need to learn MATLAB, and then learn enough about how to mode...

13 days ago | 1

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Answered
how to find the maximum symbolic value of a function with matlab
Almost certainly not gonna happen. As long as you keep all the coefficients symbolic, the result will be a fairly high order mes...

15 days ago | 0

Answered
Simulation of irrational numbers
Perhaps now I am starting to understand what your question comes down to. The ratio of x1 and x2, if they are doubles, will nev...

15 days ago | 3

| accepted

Answered
How to cut a 3D object using a plane and deleting the part above the plane, but creating new faces/vertices based on the points to ensure that the geometry below the cut is maintained?
Pretty simple really. Just the execution that takes some effort. Identify any simplex that has all vertices above or below the ...

17 days ago | 2

| accepted

Answered
how to select a set of numbers randomly which meets a condition
Lol. Ok. I'll give a new answer since the old was was on a different set of constraints. Lets see. With the new set of constrain...

17 days ago | 1

| accepted

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