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John D'Errico


Retired

4,497 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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natural cubic spline interpolation
Learn to use the debugger. This is a basic problem. You know what line the problem is on, but even if you did not, then you coul...

約18時間 前 | 0

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Finding intersection using Newtons method
Firt, why are you writing rootfinding code, when tools like fzero exist? Don't write poorly written code when well written code ...

約22時間 前 | 0

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Is there any way to use intervals(Intlab) instead of real numbers when optimizing in Matlab?
The simple answer is, you probably can't. Think about how an optimization might work, Newton's method, for example. Given a st...

1日 前 | 0

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Why doesn't my fit converge?
Assuming you have some good reason to want to do this (something I seriously doubt is a good reason)... Why is it not convergin...

2日 前 | 0

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Assume and find different possible unknown variables of inequalities , Need help please
First, you cannot write a pair of inequalities that way in MATLAB. It works as a conventional form, because people know what you...

3日 前 | 0

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How to solve this system of ODEs
You have ONE equation, not a system of ODEs. (a * dy/dt) + (b * y) = (c * dx/dt) + (d * x) But suppose you knew the true so...

3日 前 | 0

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isprime function seems to have poor performance
First, using isprime to test for primality of a Mersenne number is a bad idea. The Lucas-Lehmer test, is as I recall, much more ...

4日 前 | 1

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How can I solve a complicated symbolic integral
Your need is not relevant. Mathematics is not something that just works because you want it to. (Unless you have a magic wand, a...

4日 前 | 1

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MATLAB for invoice comparisons
Of course it can. It would require learning MATLAB. It would require a clear understanding of what you are comparing, and what ...

5日 前 | 0

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Integers can only be combined with integers of the same class, or scalar doubles.
READ THE ERROR MESSAGE! R = uint8(1:5); >> R./double(R) Error using ./ Integers can only be combined with integers of the ...

5日 前 | 0

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How to change non zero value into 0?
You want to reset the last 10 non-zeros to zero, in each column. So, let me build an example matrix. A = rand(20,5) > 0.25 A =...

5日 前 | 3

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How to generate matrices that satisfies constraints on sum of row elements and sum of column elements?
You have 9 unknowns, with 6 linear equality constraints. The unknowns are bounded between 0 and 100. You don't say an upper boun...

9日 前 | 1

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Matrix Equality Check Failed Using == and isequal
NEVER test for exact equality of floating point matrices. It won't happen, at least not unless you are very, very lucky. a_inv ...

10日 前 | 0

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randperm non uniformly distributed
Sigh. This is NOT a question of non-uniformity. Just a question of not understanding how to recognize non-uniformity, and partia...

11日 前 | 1

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How to plot below multivalued function
But it is not a function, in some standard mathematical sense of the word. https://en.wikipedia.org/wiki/Function_(mathematics)...

11日 前 | 0

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How to do discontinuous piecewise linear model fitting?
SLM is not designed to solve the discontinuous linear case, nor would I ever decide to modify the code to allow that. (Sorry, bu...

11日 前 | 1

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lagrangian polynomial function giving the incorrect answer
A good try at some code, with three errors in it. Well, essentially two errors, but you made one of those errors twice so I'm no...

12日 前 | 2

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Vector integration; is this the most correct and/or accurate calculation?
This is a slightly complex question. Is it the correct use of trapz? Of course. Is it the most accurate possible way to integr...

12日 前 | 0

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how to pick up all combination of numbers from multiple vectors
Don't store your vectors separately. Instead, learn to use tools like cell arrays, which make things hugely more efficient. V =...

12日 前 | 2

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How can I solve the non linear algebraic equation system with a parameter
You CANNOT use fsolve with a symbolic parameter in the problem. CANNOT. Fsolve is a numerical tool. It finds a root (if it can t...

13日 前 | 0

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How can I solve a sparse linear system efficiently in MATLAB?
B changes in each iteration. It is different. We are given no clue as to how it changes, or how much. We don't even know anythin...

13日 前 | 0

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Repeat numbers of X based on Y to produce Z
help repelem

14日 前 | 0

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Finding cube with most Values
Why would you expect there exists built-in code to do something totally unusual like this? Built-in code is written to solve com...

14日 前 | 0

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Fitting Gamma to a curve with two peaks
This is a mistake that many people make. They know how to fit a model to a curve. But the model they know how to use does not ...

15日 前 | 0

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Determining values in array (of 1s and 0s) that neighbour similar values
As an alternative to a tool like imerode, you can just use conv2. The minor virtue is that conv2 lives in MATLAB proper, with no...

15日 前 | 0

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How to calculate of average numbers every n rows?
Pretty easy. What you need to learn is how MATLAB stores numbers in an array, how to reshape things so that you get what you wan...

15日 前 | 1

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Deleted surf script on system
Sorry, but we cannot send you a copy of code. However, you can just download a new copy of MATLAB. Go to the support page. htt...

15日 前 | 0

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hook for an optimization problem.
That is a bad idea. You want to adjust your objective function in an optimization, based on iteration count, or some other info...

16日 前 | 0

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Fibonacci sequence up to first 256 elements
While this is surely homework, you got it almost correct, with a few major errors. Preallocate the vector!!!!!!!!!!!!!! Never ...

16日 前 | 0

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How to work rdivide function
Please don't post answers to questions as you did to another question when you just want to ask a question. Regardless, it look...

18日 前 | 2

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