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John D'Errico


Retired

4,230 2006 年以降の合計貢献数

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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Problem using boundary and trisurf functions to create a mesh with three points
You have THREE points, in a 3 dimensional space. How many points determine a volume in 3-d? 4. Essentially, a tetrahedron in 3 ...

約7時間 前 | 0

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Why is det(x) better than rcond(x) in determining non-singularity here?
Let me suggest that you misunderstand det, and why it is a terribly poor tool to use to learn if a matrix is singular or not. Ye...

約9時間 前 | 2

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Create Matrix with zeros, ones and some numbers.
Far fewer numbers required... dec2base(hex2dec({'1','1','1E23B','6069','D508F'}),10) - '0' ans = 0 0 0 0 ...

約13時間 前 | 1

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SVD issue calculating null basis
The problem is that while the last element of s is small, it is not technically zero. s s = 3.17982071419273 ...

約19時間 前 | 1

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I need matlab code for cot(x) Taylor Polynomial Function
I think what you do not understand is how to build that series expansion. A Taylor polynomial would be of the form: P(x) = ...

約19時間 前 | 0

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I want to mesh a square element with a circular hole in the middle
Use polar coordinates. Surely you know the equation of a circle in polar coordinates. r = r0 What is the equation of a unit ...

1日 前 | 1

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Symbolic solution of Transcendental equation
Sorry. Not every equation you might choose to write down on paper has an analytical solution. Some forms arise sufficiently ofte...

1日 前 | 0

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Undefined funcion 'bspline_f'
which bspline_f 'bspline_f' not found. It does not appear that bspline_f is a part of MATLAB. That is, it is apparently not su...

1日 前 | 0

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How to draw a perpendicular line using a point and slope
You want to "find" it? Or you want to draw it? The midpoint of the line segment is at (P1 + P2)/2 ans = 379.5 ...

1日 前 | 0

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How to randomly shuffle neighbouring elements in a matrix ?
You can't easily talk about the probability of two specific elements being exchanged, because things are not independent. For ex...

2日 前 | 0

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Write a function called under_age that takes two positive integer scalar arguments: age that represents someone's age, and limit that represents an age limit. The function returns true if the person is younger than the age limit. If the second arg
This is not an error. It is a failure of your code to work as it is supposed to work by your goals. What did I say? What has EV...

3日 前 | 0

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How do I plot a certain interval?
I'm confused. That you are not using x-values does not seem relevant. You plotted Mc on the horizontal axis. Next, the line: f...

3日 前 | 0

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Create an accurate boundary around 2D point cloud horizontal plane
As I thought about your problem, there is a simple solution. This is a TSP - a Traveling Salesman Problem. You want a closed sol...

3日 前 | 0

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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...

3日 前 | 1

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Just how random are random numbers in MATLAB?
The random number generation scheme in MATLAB is fairly sophisticated, having evolved greatly over the years. It is currently us...

4日 前 | 0

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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...

5日 前 | 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 ...

5日 前 | 2

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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...

6日 前 | 1

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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...

6日 前 | 0

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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...

6日 前 | 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. ...

6日 前 | 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 ...

6日 前 | 0

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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...

7日 前 | 0

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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...

7日 前 | 0

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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?...

7日 前 | 1

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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, ...

7日 前 | 1

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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...

7日 前 | 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...

7日 前 | 1

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

8日 前 | 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...

8日 前 | 2

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