John D'Errico

Retired

Last seen: Today | Active since 2006

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A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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Answered
Solving linear system modulo prime^n when matrix is univertable
You can't use LU anyway, since it is not designed to work on that problem. Nor can you use slash or backslash, which again, do n...

13 hours ago | 0

Answered
Differentiating inside a matlab function
Oh, you were so close. Actually, you did not even need to tell diff what variable to differentiate with respect to. syms x(t) ...

2 days ago | 0

Answered
How to generate an prime random number??
A random prime? Impossible to do. That is, something that many seem to misunderstand is you cannot generate a random number on s...

3 days ago | 0

Answered
How to make multiple lines of best fit into one scatter graph
Is it possible to do in MATLAB? Of course it is. It of course depends on the skill of the person writing the code. It depends on...

4 days ago | 0

Answered
Find best fit curve from multiple curves of different size
On the right end, you have an infinite slope. On the left end, not so much of a problem. But it will be better to do a couple of...

4 days ago | 0

Answered
How does interp1 work?
Why not post the actual data you used that caused the problem, instead of only a tiny fragment of it? You certainly CAN post t...

5 days ago | 2

Answered
Matlab Dimpulse function documentaion not found
It seems dimpulse (or at least one version thereof) can be found in the control TB. which dimpulse -all However, given the loc...

5 days ago | 0

Answered
part 3 example was wrong
Answers is not official MATLAB support. So telling us a problem exists does nothing. Contact support directly. https://www.ma...

7 days ago | 1

Answered
I'm trying to find solutions to variables in a system of non linear eqations, that represent a geometrical puzzle.
A problem is, we don't actually know what is the geometric system you are trying to solve, nor have you told us the solution you...

8 days ago | 0

Answered
Integrating a very long expression containing symbolic values
Is there some law of mathematics that everything you can or will write down has a solution? (No.) That int did not find a soluti...

8 days ago | 0

Answered
Can someone help me fix my bisection function?
Good code. Well, at least in terms of the documentation. Excellent in that respect. Readable code is important when you need to ...

9 days ago | 0

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Answered
What is the interpolation algorithm behind MATLAB’s pcolor with FaceColor = 'interp' that creates sharp, defined boundaries？
There are three simple ways to interpolate inside a 2-d rectangular region. But two of them are analogues of each other. First,...

9 days ago | 0

Answered
How to compute the characteristic equation given the eigenvalues?
You have not asked this question as if it is a homework assignment, so I'll give an answer. The characteristic equation GIVEN e...

11 days ago | 0

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Answered
How to download old version of toolbox?
You cannot. That is, you cannot use an old toolbox for a previous release in a newer release of MATLAB. So what can you do? You...

11 days ago | 0

Answered
Bug with large HEX numbers
H = 'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141'; numel(H) So 64 hex digits, which would yield an intege...

12 days ago | 1

Answered
How to get consistant results when testing code performance
A single time test will be susceptible to anything that attracts the attention of your CPU. And sadly, your CPU suffers from com...

13 days ago | 0

Answered
update guess in fsolve
Um, no, You cannot always find a way to "update" your initial guess for fsolve. One can even prove this to be true. You can cha...

14 days ago | 1

Answered
How to remove columns in very large matrices.
GET MORE RAM!!!!!!!!! RAM IS CHEAP!!!!!!!! Need I say it again? You have a quite large array. (1.75e6*2000*8)/1e9 That arra...

15 days ago | 1

Answered
using sparse matrix and vpa function simultaneously
I wanted a nice bright red Lambo for Christmas. Nope. Did not happen, nor was it ever going to happen. The same applies to you. ...

15 days ago | 0

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Answered
Matrix is singular to working precision
I don't even need to run your code, to see an obvious mistake. In fact, I knew what I expect to be a problem, even before I look...

17 days ago | 0

Answered
real and integer variables
No. We won't do what is surely your homework assignment. But why not TRY IT! First, plotting it is trivial. LEARN TO USE a tool...

25 days ago | 0

Answered
Why matlab is not as intelligent as python
Why? Why is anything the case? Because it is. Because they are two different languages, with different capabilities, and differe...

26 days ago | 3

Answered
Matlab sparse matrix does not come out as I would expect
S=sparse([1 3 2 1 4],[3 1 4 1 4],[1 2 3 4 5],4,4) full(S) It works just fine. What did you do wrong? LOOK CAREFULLY AT WHAT Y...

27 days ago | 1

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Answered
defining upper and lower limits of a matrix
Is there any way to set the min and/or maximum values of the elements in a matrix, and do so automatically? NO. Well, not withou...

1 month ago | 1

Answered
how to optimize block toeplitz matrix ?
The one thing you NEVER, EVER, EVER want to do is stuff the elements into a sparse array iteratively. NEVER DO THAT!!!!!!!!!!!!!...

1 month ago | 0

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Answered
PC specs for heavy & complex simulations
No computer will ever be as fast as you want it to be. Even if you do get the fastest, most powerful computer you can possibly ...

1 month ago | 0

Answered
Which statistic is minimized in curve fitting app
The sum of squares of the residuals is mimimized. SSE effectively stands for Sum of Squares of Errors. What is the 2-norm? Just...

1 month ago | 1

Answered
I need to draw a shape in matlab help me
This is not a difficult problem. Not at all. But it is impossible for us to do it, based on having been given no information exc...

1 month ago | 0

Answered
Simmetrical Constraints in Multivariate Regression
Now please stop asking this question. I already suggested 3 ways you MIGHT solve it, the first time you asked. You could have ad...

1 month ago | 0

| accepted

Answered
Find limits satisfying a condition on an integral
You have posed a interesting problem, with a subtle flaw that possibly you don't understand. You asked to find an integral limi...

1 month ago | 0

John D'Errico

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