Community Profile

# John D'Errico

### Retired

3,463 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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Strange results when adding two vectors
Nope. Not insane. Just part of MATLAB, since the last few releases. Nor can you turn it off. If you don't like it, just don't ad...

1 hour ago | 0

Solve for x in an algebraic equation
You can recognize that it is easy to write an equation that has no analytical solution? In fact, you just did exactly that! Yes,...

11 hours ago | 0

Vectors and Sum operation
R = 1/sum(1./y); y is a vector. You want to divide EACH of the elements of y into 1. So you use the ./ operator, which is d...

11 hours ago | 1

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exp(infty1) * erfc(infty2) = NaN
You have several choices. 1. Use the symbolic Toolbox, which can handle high precision computations. x = sym(200); v...

1 day ago | 0

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Hello, Quadratic and power curve fitting
What do you expect? As you generated it, we see: f_exp f_exp = Columns 1 through 13 6360.5 10567 ...

1 day ago | 0

symbolic equation Empty sym: 0-by-1
Being new is irrelevant. This is just a question of mathematics. Sym produces an empty result because there is no analytical sol...

1 day ago | 0

why is my plot shows nothing?
Because you need to read the getting started tutorials for MATLAB? In 3 simple (truly basic) lines of code, I see 4 significant ...

1 day ago | 3

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how to convert logical into charactor
To answer the question you insist on asking multiple times. L is a logical vector. C a character array. L = rand(10,1) <...

1 day ago | 0

how do I make a temperature data matrix as sparse matrix
data = [1901 22.4 24.14 29.07 31.91 33.41 33.18 31.21 30.39 30.47 29.97 27.31 24.49 1902 24.93 26.58 29.77 31.78 33.73 32.9...

2 days ago | 2

Works for me. A=[6 5 6;2 4 1]; A(2,2)-A(1,2) ans = -1 I would suggest that A is probably of class uint8....

2 days ago | 0

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Sparse Matirx
From what existing matrix? In what form? If you already have a matrix, then the sparse function will convert it to sparse for...

2 days ago | 0

How can I plot a function of 2 variables which are dependent on another one?
So this is really a function of ONE variable, not two. Yes. There are intermediates in the computation. So what? t = 0:...

2 days ago | 0

orthogonal matrix with different size of rows and columns
So can you do what you want? If your goal is to find a set of n vectors of length d, such that they are orthogonal to each other...

2 days ago | 0

Passing predefined variables into matlab's fit function
Lots of ways I guess. To make it all explicit, here is an example of one way: % a fixed parameter: E = 1.25; % some...

3 days ago | 1

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is this a scam
This is the internet. NEVER trust anyone that willing to offer to do your work, and all you need to do is pay them for the servi...

3 days ago | 0

Surface Roughness of 3D Scatter Plot
Despite the little information you have given us, conspicuous in its absence is what we are not told. So while KSSV MIGHT be on ...

4 days ago | 0

Getting vertcat error, not using vertcat
Your code: ID=5415; K=ID/1000; uts=1; uph=0.5; a=0.05; b=1.5; for n=1:100 k5(n)=a+(b-a)*ra...

5 days ago | 0

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Function lsgnonneg - I have used this function, but the results are not good.
ARGH! For a matrix of this size, save it using the save command!!!!!! Saving the array as a text file, with file type .mat is NO...

5 days ago | 0

Find plane equations given two parametric line equations
The biggest trick here is to learn to use MATLAB! MATLAB is a vector & array language. So learn to use those capabilities. Fi...

5 days ago | 1

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Curve fitting 3d closed surface
Not completely trivial. Yes, you can use regression tools to try to estimate the parameters of a conic form etc., but you would ...

6 days ago | 0

fsolve stopped because the problem appears regular
Why in the name of god and little green apples would you use fsolve to solve for the roots of a 1-d polynomial problem? Oh. Yes....

7 days ago | 0

how can i generate real random numbers?
First, they are not truly random if you use a computer and an algorithm. They will only be pseudo-random. So they will at best h...

7 days ago | 0

How to find u value at a point on cubic curve
So you have 4 points on a parametric curve, thus (x(u),y(u)), for 4 values of u? Just use polyfit, getting a cubic for x(u), ...

7 days ago | 0

Inaccurate roots found using Newton Raphson method for 2 variables
One of the first things I ALWAYS tell people to do, especially when they see something confusing to them, is to plot EVERYTHING....

7 days ago | 1

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Logical Vectors and &
The & operator works on the elements of the two variables element-wise. Since All elements of B are 0 (false) and it is true ...

8 days ago | 0

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how can I write a multiplication of variables to graph?
MATLAB does not know that you have decided that xy is the product of two variables. Mind reading is not a strong point for compu...

8 days ago | 0

5th root with Newton-Raphson code
What is wrong? I'd start by pointing out that this is NOT Newton's method as you wrote it. https://en.wikipedia.org/wiki/Newt...

8 days ago | 0

Function inside function - generating Random Walks
As far as why that error occurs, LOOK AT YOUR CODE! READ THE ERROR MESSAGE! "Output argument "p" (and maybe others) not ass...

8 days ago | 1

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Hide random values from matrix
There are lots of ways you could "hide" something. Simplest would be to make a copy of your matrix. Then choose some subset o...

9 days ago | 0

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Submitted

Partitions of an integer
List all partitions of an integer