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John D'Errico


Retired

Last seen: Today Actif depuis 2006

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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A répondu
How to recover original raw signal from filtered results given filter coefficiencies?
Is it possible? NO. Sorry. Mathematics does not give you a trash can, where this operation can be undone. Information content wa...

environ 8 heures il y a | 0

A répondu
Inverse of a symmetric matrix consisting of submatrices is desired.
This makes little sense as you write it, AND it will be essentially impossible to perform in MATLAB using symbolic tools. syms C...

environ 14 heures il y a | 0

A répondu
Solving equations using Newton-Raphson method for 7 equations with 7 variables
As @Torsten said, this is a LINEAR system of equations. Nothing nonlinear needed. In fact, you can use many tools in MATLAB to t...

1 jour il y a | 1

A répondu
Need help with a system non-linear equation with three variables
Simple. Use lsqnonlin. There will almsot certainly be no exact solution. All you can do is find a parameter set that minimizes ...

1 jour il y a | 1

A répondu
read text file to get complex number
Read the files in as two vectors. There are many tools that can read a text file. Then add them, multiplying the second by sqrt...

1 jour il y a | 0

A répondu
GA does not solve problems with integer and equality constraints
The coupling of equality constraints with integer constraints makes a significant problem. For example, suppose I wanted to solv...

1 jour il y a | 0

A répondu
problem with low infinite number
They only look the same, to 4 decimal places. format short x = 1.23456789; y = 1.23456987; [x,y] They certainly look the s...

1 jour il y a | 0

A répondu
How to display this whole data simultaneously?
What can you do? This will mainly be in your MATLAB settings, first, under the command window tab. Here, you can control how man...

2 jours il y a | 0

A répondu
Fittype issue: unrealistic results and problems with upper and lower bounds
Star pointed much out to you, but I want to say a few extra things, and the fit he got was relative crap due to the terrible cho...

2 jours il y a | 1

A répondu
integration in matlab plot
You CANNOT use trapz. Despite the fact that another poster has done so, that does not yield a result up to 4.7. If you have no d...

3 jours il y a | 3

A répondu
2023b Compatibility with 2019b code?
Is there a limit? No limit is ever published. The first is a warning, NOT an error message. It is intended to tell you there wil...

4 jours il y a | 1

A répondu
Find Area under the curve as a non negative
You don't show your data, so I need to make something up, and I'm guessing what your problem is, because your question is confus...

4 jours il y a | 0

A répondu
Problem with non-Zero Matrix Appearing Zero in Command Window and in Imagesc
They are still (non-zero) numbers. Just too small to display in the chosen format. If you close your eyes, the world does not di...

5 jours il y a | 0

| A accepté

A répondu
str2double with long string seems to give wrong answer
Do you appreciate that str2double will convert the number to a DOUBLE PRECISION number? Of course it must, as why would it conve...

5 jours il y a | 3

A répondu
How to use for and if statements together?
Can you compute the overall mean? Surely you know how to use the function mean. If not, can you compute the overall mean? How wo...

5 jours il y a | 0

A répondu
Why Matlab is always giving the same error while putting comment to reply in quesiton?
MATLAB is not doing anything of the sort. In fact, that is not a response from MATLAB at all, but from the web site, from MATLAB...

5 jours il y a | 0

A répondu
Solve a system of linear equations
I am confused. You say that you know how to solve the problem using lsqnonneg. So just use it! n = 30; Y = rand(30,n); S = r...

6 jours il y a | 0

A répondu
generating every possible trajectory in a workspace
Um, no. There are infinitely many possible trajectories, if we consider the variables as continuous. But even if all variables w...

7 jours il y a | 0

| A accepté

A répondu
How do I request participation or sponsorship from MathWorks on behalf of my social organization at my University?
Answers is not the correct place to ask your question. Instead, I would contact support directly. Possibly through this link: h...

7 jours il y a | 0

A répondu
Solving tridiagonal Matlab matrix using Gauss siedel ( can't use other method )
Why in the name of god and little green apples are you using Gauss-Seidel for this? (I can only assume this is a homework assign...

7 jours il y a | 1

| A accepté

A répondu
How do I change my code so that the numbers 1112, 2111, 1211 or 1121 work in this code to reach Kaprekar's Constant?
Numbers in MATLAB do not have leading zeros. Sorry. That is not a valid number, just a string of numeric digits. If you need le...

8 jours il y a | 1

| A accepté

A répondu
What Does the Symbolic Math Toolbox Mean by 0 < s When s is Complex?
Just test it yourself. :) Admittedly, it may not have been obvious to perform this test. But we can use it to learn how MATLAB s...

9 jours il y a | 0

| A accepté

A répondu
how can I calculate my expression with double integration?
The important takeaway to use is, you CANNOT perform arithmetic operations between a pair of function handles. Maybe you think y...

9 jours il y a | 0

A répondu
fsolve with bound constraints - transformation method
The transformation need not be one to one. For example, a common and reasonably good way to perform an optimization subject to b...

10 jours il y a | 0

| A accepté

A répondu
How to get a random possible solution from 'solve' function when getting unknown parameters z1 and conditions
Solve cannot return a random possible solution. Wanting code to do what it is not designed to do will never be sufficient. If ...

10 jours il y a | 1

| A accepté

A répondu
How to get a surface plot for the given function to know how many minima are there?
You cannot plot 4 independent variables. In fact, you would need 5 dimensions to plot, since you want to plot the result of that...

10 jours il y a | 0

A répondu
I can't comput the following commands
Sure you "can". It is just that MATLAB fails due to an error. :) Anyway, you seem to think an if statement applies to each elem...

11 jours il y a | 0

A répondu
How to plot four variable vector-valued function in MATLAB?
It is no problem. Well, at least not if you have a hyper-dimensional holographic monitor. (Mine is broken, and awaiting parts de...

12 jours il y a | 0

A répondu
Not auto change sec(x) to 1/cos(x)?
The problem is, which form is simpler? Simple in your eyes need not always be simple in the "eyes" of your computer. The point ...

12 jours il y a | 0

A répondu
How to count how often a variable returns to zero and then increases from zero
It appears this parameter never goes negative. Are your sets ALWAYS such that a zero is always alone? So when it hits zero, it ...

13 jours il y a | 0

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