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John D'Errico


Retired

3,707 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
Problem In curve fitting
You won't find a function that fits any arbitrary, essentially scattered set of data. And that is what you seem to have. Anyw...

1 day ago | 0

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Answered
Simple function constrainting a polyfit with lsqlin is giving strange fits
Is this homework? It seems more sophisticated than the classical homework assignment, so I will guess not. But, sorry, just thro...

2 days ago | 0

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Answered
3D interpolating polynomial
Now that you have shown the problem you are trying to solve... I'm pretty sure I remember telling you that you should not use...

3 days ago | 0

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I have a 6x6 symbolic matrix A that I want to inverse. I am trying both inv(A) an d A\I to do the inversion. However, it takes forever (more than a day) until I stop it. My hardware is also very good. Core i7, 16 GN RAM.
People think their computers are huge. Super fast. They can do anything. So they get spoiled, expecting anything to work like th...

3 days ago | 1

Answered
Finding x such that 1 is eigenvalue
You are trying to do too much in one line. Making your code super compact does nothing, except make it unreadable. And it did no...

4 days ago | 0

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Answered
exp*prod*exp(x(lnx)^k) solving equation
Read what I said. Again. TAKE THE LOG!!!!!!! That gives you something like this: -lambda*pi*r^2*P + lambda*pi*R^2*P*(log(P)...

5 days ago | 1

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Answered
Does interp3 (with linear option) perform trilinear interpolation?
Both interp2 and interp3 use n-dimensional tensor product linear interpolation, thus respectively bilinear and trilinear interpo...

6 days ago | 1

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Answered
Order of roots obtained from function roots
Roots does not assure any specific order of the returned roots, nor should it rationally do so. Feel free to sort them in any...

7 days ago | 0

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Answered
Find tangent to set of 2D points
Your curve is somewhat noisy. I might think to point out that my interparc tool from the file exchange can be made to give estim...

7 days ago | 2

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Answered
How can I set limits to an interpolation with griddata?
You cannot set limits when using griddata, AND the 'cubic' option. It will happily interpolate smoothly as it will. But that may...

7 days ago | 0

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Answered
Is any way to Inpaint this image?
I won't touch this, and I've written the main inpainting tool on the File Exchange. Do NOT use that tool I've posted, as you wil...

8 days ago | 0

Answered
How to seperate a matrix into several parts and give names each of them?
Don't do it. There are MANY better ways to solve this. For example, convert your vector (via a simple reshape) into an array....

8 days ago | 0

Answered
skipping code sections when running the code
If this is a script, then learn how to use cell mode. Learn about live scripts. If this is a function, then learn to write...

8 days ago | 0

Answered
Best computer for problem
Which specific computer should you get? One as fast as your company will pay for, with the most RAM they will go for. Make sure ...

9 days ago | 1

Answered
How to solve algebraic equations in Matlab 2018a?
In R2018a, they finally stopped letting you just provide a string input. It has been something they have been threatening for se...

9 days ago | 1

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Answered
Finding value of unknown variable in determinant matrix, where matrix is kept equal to zero
The .jpg you show is a 3x3 matrix, NOT a 6x6 matrix. So there are obvious points of confusion in what you say. But in any case, ...

9 days ago | 0

Answered
Increase performance for null space calculation on symbolic matrix
Surely you need to recognize the difficulties here. If not, then you need to consider what is involved. Let me give a trivia...

10 days ago | 1

Answered
How do I find the mean of all the radius around a point in polar coordinates?
Are you asking how to find the mean of ALL pixels that lie WITHIN a radius of R, of some fixed point in the image? If so, the...

10 days ago | 1

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Answered
curve fit exactly the function I enter
So why do you think that a sum of two exponentials MUST fit this data? Looking at the data, that hardly seems a good conclusion....

10 days ago | 0

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Answered
problems with a trascendental equation
You probably need to start with the basic tutorials to learn MATLAB. For example, you do this: m = linspace(10,20,1) m =...

10 days ago | 1

Answered
How do I set an inline function as a parameter?
I assume you want to pass in a function to be used in your bisection code? First, don't use inline functions, unless your MAT...

11 days ago | 1

Answered
How to combine series of consecutive numbers in Matlab?
Loops are not terrible things, to be feared in MATLAB. Yes, it is true that often you can gain in speed by replacing nested loop...

13 days ago | 2

Answered
Does different MATLAB versions handle array arithmetic differently ?
In R2016 (not sure if it was a or b. I think b, but not really relevant, so will not check.) they introduced the capability to e...

13 days ago | 0

Answered
same matrix but not equal problem
When you see something that you do not understand, LOOK AT YOUR DATA. C(1,:) ans = Columns 1 through 31 NaN ...

13 days ago | 0

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Answered
Finding coefficients from factorized polynomial?
I have no idea what you are talking about. n = 3; syms x y z = (x+y)^n; c = coeffs(z) c = [ 1, 3, 3, 1] I...

13 days ago | 0

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Answered
solving system of equations using singular value decomposition and fsolve
Solving a singular (or nearly so) linear system of equations will have infinitely many solutions, all equally good (or bad). ...

14 days ago | 0

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Answered
Solve command in matlab not working?
The problem is not in solve. It is with your understanding of the mathematics. You wrote this: N1 = 76.045376620772100, ...

14 days ago | 1

Answered
if statement for error
No. You cannot use if to find an error, because an error interrupts and stops execution of your code. However, you can use a try...

14 days ago | 0

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Answered
How do I create a solid shape that has a smaller area on the bottom surface than the top surface?
Hmm. But not hard in any case. Best if the top and bottom polggons are the same length. Suppose we create two polygons. If th...

14 days ago | 0

Answered
Does MatLab run on Debian 9?
The answer to these questions is always easy and fast. Just check the system requirements. https://www.mathworks.com/support/...

14 days ago | 1

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