Community Profile # John D'Errico

### Retired

4 216 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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How to draw a cylinder that has an irregular cross section and changing along the cylinder length?
You essentially have radius, as a function of theta, and z. And I don't have your data, since all you gave us is a picture. It i...

environ 10 heures ago | 1

Is it possible to constrain the unknown x in an optimization problem to be rounded up to 1 when it originally is a value between 0 and 1?
You are trying to use a tool not designed to solve that class of problem. You cannot round the results AFTER fmincon returns a r...

environ 21 heures ago | 0

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Finding extreme points in the convex hull
Why not do the obvious? xy = rand(1000,2); >> ch = convhull(xy) ch = 55 460 890 204 908 222 189 ...

environ 21 heures ago | 0

How to plot the exterior edges only of an alphaShape
When you have a problem like this, learn how to investigate what you can do with the class. x = rand(10,1)*5; y = rand(10,1)*5...

2 jours ago | 1

Looping a matrix to find determinant
An ambiguous question, and possibly, an ambitious question too. For example, do you feel it to be of importance to test the subm...

2 jours ago | 0

is it possible to create a Character array using a vertical vector of characters?
Sadly, answers A, B, and C are all virtual drivel, as is the entire question. The difference between options B and C is silly. A...

2 jours ago | 3

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Can I analytically solve a logarithmic equation using the symbolic toolbox?
Sigh. Sorry. I typed too fast there, and I answered incorrectly. Not sure why solve does not get this. Multiply by log(u) + 1. ...

2 jours ago | 0

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Writing a one line programme to show that an equation equals to the answer shown.
Homework, but you did make an effort. Does this not show what you need to show? sqrt(4) ans = 2 Or this? sqrt(4) == 2 ...

2 jours ago | 0

Euler-Bernoulli's beam ODE or PDE
Euler-Bernoulli https://en.wikipedia.org/wiki/Euler–Bernoulli_beam_theory might appear in several aspects. It kind of depends...

3 jours ago | 0

Exiting: the problem is unbounded.
THERE IS NO SOLUTION, BECAUSE THE PROBLEM HAS NO SOLUTION. Changing the solver will not make it now a viable problem. This was e...

3 jours ago | 0

residual r=ax-b ∞-norm
Why would you possibly have expected to get the right answer? Was the infinity norm requested? Is it a 2-norm that you computed?...

3 jours ago | 1

General Approach to Fitting dozens of curves using the same coefficients
I'll suggest that while you CAN do at least something, it is perhaps not trivial. And, sadly, the result would likely be total, ...

3 jours ago | 1

Matrix dimensions must agree.
Look at line 4. y = (0.943*(x-9).^2)-(24.99*t+6113.91); We know what x is, that is, a vector. x = 9:0.1:15; But wh...

4 jours ago | 0

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Trying to solve system of equations symbolically, getting zero for solution
You have what you claim to be a linear system of 7 equations in 7 unknowns. (I've not checked this claim, carefully, but it look...

4 jours ago | 1

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Your normal distribution is one that is too narrowly defined around the mean of 350. In fact, it is effectively zero towithin to...

4 jours ago | 0

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Matlab giving incorrect graph for exponential below function
Sorry. But whatever you did in Excel is apparently flat out wrong. Lets just think about this, for a moment. Does it make even r...

4 jours ago | 2

What is the best way to smooth and compute the derivatives of noisy data?
The "best" way? That will be completely dependent on your data, on what you know about your data, and on what you are willing to...

5 jours ago | 1

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Assignment support in Sparse Matrix
Answers is not a homework service, so I will not do your homework for you. However, this question is one that I would argue is c...

5 jours ago | 0

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Average of two closed curves
Given two closed curves, say a circle and a square, I would first formulate the problem as a pair of functions in polar coordina...

6 jours ago | 1

Getting a maximum from a fitted curve (smoothing spline)?
Where does the problem lie? Are you surprised that the spline does not pass through the maximum data point? So are you just aski...

6 jours ago | 2

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MATLAB code that can replace the inbuilt function 'norm'
I suppose I can write a simple 1-norm code, that will work for a vector OR matrix. Thus, the 1-norm of a vector is the sum of a...

7 jours ago | 0

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Fitting an Equation on to graph
Easiest is if you just use the curvefitting toolbox, OR the stats toolbox, OR the optimization toolbox. Still easy enough to us...

7 jours ago | 0

how to move a sphere until it intersect a surface?
You have a surface defined as Z = x.*exp(-0.1*x.^2 - 0.2*y.^2 + 1.5); fsurf(Z) xlabel X ylabel Y zlabel Z And a sphere, ...

9 jours ago | 2

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Poisson distribution-for loop not working
It is impossible to know. What is x(1)? What is x(2)? I would suggest that you look at those numbers. For example, suppose x(1) ...

9 jours ago | 0

Can I solve for multiple variables in an equation?
Sigh. It looks like this is a followup to your last question. But it is COMPLETELY different. And you cannot use randfixedsum, w...

11 jours ago | 0

problem with genetic algorithm contain on linear inequality constraints
In general, this is a really bad way to create ANY matrix. Why? Because the probability of a typo approaches 100%. I do not know...

12 jours ago | 0

Trying to use Wiener filter to remove blurr and noise, get a matrix of NaN, why?
You want to do this yourself. So you need to learn to fix the problem. You fix it by learning how a NaN is created, AND by learn...

12 jours ago | 0

Numerical Integration on Discrete Data Sets
I might first guess that your data is not uniformly spaced. Simpson's rule does not apply to non-uniformly spaced data (thus non...

13 jours ago | 1

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