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John D'Errico


Retired

4,143 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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Facing a problem in calculating the sum of digits of 100!.
It looks like this question has gotten enough interest that it deserves a complete answer on how to do it using MATLAB. And sinc...

約12時間 前 | 4

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parabola wont show up?
fplot(@(x) -3.*x.^2+5.*x+10)

約15時間 前 | 0

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My plot does not show anything
delta is a scalar. plot does not work well when one of the arguments is a scalar. I suppose some might call if a feature that ...

約15時間 前 | 1

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Why does the solve function give me matrix instead of a number ?
You get 3 values, because there were 3 solutions found. You can convert them to numbers using vpa. syms z vpa([root(z^3 - (3...

約15時間 前 | 0

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how to represent the purple color by a string value
You can't. MATLAB offers those string options for colors. If you want to set a specific color, you can, but as a numeric vector ...

約15時間 前 | 0

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Hello everyone, Can I use predefined scattered values for the variables used in Genetic algorithms instead of ranges?
Well, you can, IF that is correct for your problem. For example, suppose you knew that you wanted variable x to take on 5 diff...

約16時間 前 | 0

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Devide N points to S sets (all possible combinations)
All possible combinations? Seriously? 100 numbers, into all possible subgroups of 5 groups, or so? Roughly? Must all groups be t...

1日 前 | 1

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Please can anyone clear my doubt regarding Concatenation of data.
Sorry, but there are soooo many reasons why you do not want to create those numbered variables. Having now done so however, you ...

1日 前 | 0

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link this set of equations to a single unknown
Not gonna happen, well, not easily. For multiple reasons. You have a totally symbolic matrix A? Or are those all fixed numbers? ...

1日 前 | 0

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Element wise multiplication .* rounding problem
Nope. It does not. Welcome to the wild, whacky wonderful world of floating point numbers and arithmetic. A place where computati...

1日 前 | 2

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3D point cloud
You need to learn to use the debugger. Or you need to learn to provide sufficient information, with the complete error message t...

1日 前 | 0

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modifying vectors help.
When all else fails, throw it at polyfit. (Well, actually, I know polyfit will work here, so it really is not a code of last res...

2日 前 | 0

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Solve for symbol not finding explicit solution
And you "know" a solution exists? What is it? Not all problems have an analytical solution. How is it that you assert a solution...

2日 前 | 0

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issorted alternative for optimization toolbox
Apparently not. However, you don't need it either. What stops you from just using a cumulative sum? Then constrain all elements ...

3日 前 | 0

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i need a rough k means code anyone help me plzz ...the following code has some errors.
Easy, peasy. It is right here: https://www.mathworks.com/products/statistics.html Writing your own code to do what others have...

3日 前 | 0

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picking those matrices whose determinant is greater than 0
WTP? if b > 0 disp(a) end

3日 前 | 0

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How to add custom equation for fitting
You are over thinking things, thinking you need to use sum, etc. What is a polynomial model? What do you have? What are the unk...

3日 前 | 0

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use more digits in computing in matlab
Sorry. Unfortunately, you cannot simply request more precision in your computations in MATLAB. The trick is to learn to do your...

3日 前 | 2

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I have a large vector, I would like to find a set of data which is a subset of the large vector.
ismember is exactly the tool to solve your problem. A = [1 3 5 7 9 8 6 4 2]; B = [5 6]; [LIA,LOCB] = ismember(A,B) LIA = ...

4日 前 | 1

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Switch to write programs
You could write a switch statement for this. The problem is, since each case does a different thing, you effectively need 100 di...

5日 前 | 1

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Double vs Single Precision, Matlab in 2019
This topic is worth discussing. X = zeros(10,10, 'single'); The construction: X = single(zeros(10,10)); is four times slower!!...

5日 前 | 0

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how to decrease precision
You cannot tell MATLAB to use an arbitrary lower or higher precision. At most, you can work in single precision instead of doubl...

6日 前 | 0

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pick numbers from matrix with probability
This is one of those question that are almost impossible to answer, because your goal is so fuzzy, too unclear to write code to ...

6日 前 | 0

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How do i plot 3 langrange polinomials in one figure?
Do you know how to plot ONE such polynomial? I hope so. If you do, then you need to use the hold command. That is, after you plo...

6日 前 | 0

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Create binary vectors with specific hamming distance
Why does this seem pretty easy, if you just think about what Hamming distance means? https://en.wikipedia.org/wiki/Hamming_dist...

6日 前 | 0

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How to Show 1/4 in 1/2^2?
Do you mean this? format rat 1./(1:10).^2 ans = 1 1/4 1/9 1/16 1/25 ...

7日 前 | 2

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It shows: Undefined function 'vpasolve' for input arguments of type 'double' when I run it. Can I know how to solve this?
Is f a symbolic variable? (No.) We see this: syms f f=zeros(rr); fn=1+2.*sqrt(f).*log(((rr)./3.7)+(2.51./(Re.*sqrt(f)))); f...

8日 前 | 0

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Exponential Fitting function not plotting the same information as the data points?
Where should I start? :-) A terribly important feature of ANY exponential model is you absolutely, positively need good start p...

8日 前 | 0

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Averaging every element with nearby elements
A simple solution is to use conv2. It works quite well inside the domain. But then you will need to be careful around the edges....

10日 前 | 1

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How to find the nearest pixel to the point attained by ginput() on the curve
Simple is to just extract the curve in terms of pixel coordinates. So you will have a list of points along the curve. Then use ...

10日 前 | 0

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