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John D'Errico


Retired

3,825 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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Answered
How to find all solutions to a function?
This could be a deflating experience. ;-) x(1) = vpasolve(f) x = -1.8454863060096746759606364851789 >> x(2) = vpas...

2 hours ago | 0

Answered
How can I get a value not NaN when calculating ''inf/inf''?
There is no consistent numeric value you can obtain when taking the ration inf/inf. Should it be 1? Clearly x/x is always 1, ...

4 hours ago | 0

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Answered
How to calculate a derivative of function numerically?
You can use symbolic tools to compute the derivative, if you have that toolbox. But if you wish todo so numerically, then you ne...

1 day ago | 0

Answered
How to permanently set the search path?
Once your search path has been established, using tools like pathdef, addpath, rmpath, userpath, path, pathtool, you can then us...

1 day ago | 0

Answered
How do I display even numbers between A and 100 in one single column?
How do you turn a row into acolumn? Use reshape. Or, use transpose. Or, use V(:) In any case, all will create a co...

1 day ago | 1

Answered
I have ( An ) matrix, I need generalised algorithm to calculate An-1 = An *B. Here An-1, An, and B are matrices.
You have A3, and you want to compute A2 and A1? A2 = A3*B; A1 = A2*B; You want a general "algorithm"? DON'T DO IT....

2 days ago | 1

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Answered
Zscore and solving by definition differ
Source? Basic mathematics. An eigenvector is NOT unique. If A is a square matrix, with eigenvalue lambda, and eigenvector X, ...

2 days ago | 0

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Answered
Numerical Garbage value in Matrix
help real Better yet, compare the results of abs(real(A)) to abs(imag(A)). As long as the imaginary part is small, just del...

3 days ago | 1

Answered
How to force a exponential fit to go through a preestablish point (x,y)?
'StartPoint' refers to the initial parameter guess for the model, since this is an optimization problem. Not a point the curve m...

3 days ago | 0

Answered
How likely is it that I can use simple linear regression to predict?
No real world data truly follows a perfectly linear model. Even where there is an essentially linear domain, there are always li...

6 days ago | 0

Answered
Order of logical operators
You need to recognize how MATLAB evaluates a logical expression. Many people use that shorthand, to indicate two coupled compari...

7 days ago | 1

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Answered
is it possible that answers can be accepted?
Being an MVP does not give you the privilege to doubly accept an answer. Read the help for Answers. It tells you what privileges...

7 days ago | 1

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Answered
Plotting the area defin
You know how to use meshgrid! In fact, I know that, because you used it in your other question. So it you want to plot someth...

7 days ago | 1

Answered
Start point power law fit
I'm not positive what tools you are using for the fit. I will assume the curve fitting toolbox. Almost all optimizers (nonlin...

8 days ago | 0

Answered
Looking for some tips on a Simulation Project!
Is there a better way? Not really. In fact, your plan is actually a good one, and arguably the best approach. The true art will ...

8 days ago | 1

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Answered
assemble global stiffness matrix
K = zeros(10,10); k = [1 -1; -1 1]; for n = 1:9; rind = n + [0 1]; cind = rind; K(rind, cind) = K(rind, c...

8 days ago | 0

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Answered
Create a polar function from a polar regression
Your question is slightly ambiguous. Are you looking to find a model of the form z=f(r,theta)? Or do you want some model that li...

9 days ago | 0

Answered
What are Contour Levels
A contour of the function z(x,y) is a set of points in the (x,y) plane, such that z(x,y) is fixed at some constant value. That c...

9 days ago | 0

Answered
Operands to the || and && operators must be convertible to logical scalar values
LEARN TO USE THE DEBUGGER!!!!!!!!! I did this: dbstop if error Next, I ran your code. Well, I tried to run it. f...

9 days ago | 3

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Answered
Exponential fit using Linear Regression
Write down the model you want to use. DO IT! You can't solve this unless you understand & think about what you are doing. That r...

10 days ago | 0

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Answered
How to calculate the ratio of two primes in a given set of primes?
As long as the set is sorted, you never need to worry about the ratio being greater than than 1. How do you compute a base 3 ...

11 days ago | 1

Answered
gamma function for N>100
No. You will not make it work for large values, when they exceed the limits of gamma itself. Your code is not better than what y...

12 days ago | 1

Answered
find rows of Zeros in matrix
Time to learn MATLAB. How do you find that something is zero? A == 0 That returns 1 where an element of A is zero. EXACT...

12 days ago | 1

Answered
If statement with many logical or.
Your problem is EXACTLY in that you are trying to compare floating point numbers, for exact equality. This is something you shou...

12 days ago | 2

Answered
Function not defined but it is in fact defined
Did you actually save it as an m-file? Is it saved to your search path? NOT saved in one of the MATLAB supplied directories? ...

13 days ago | 0

Answered
Volume of irregular shape
Not sure I see the problem. You apparently have cross sections in say x and y, presumably, at various values for z. That means y...

13 days ago | 0

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Answered
How to make an exponential function taking as input a vector?
inp = 3; syms n n.^(0:inp-1) ans = [ 1, n, n^2]

14 days ago | 0

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Answered
How can I do least square problem to get certain area?
Compute the area of the polygon. I'll call it A. polyarea should suffice. Recognize that area scales with the square of the u...

14 days ago | 0

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