John D'Errico

Retired

Last seen: 2 dagen ago | Active since 2006

Followers: 30 Following: 0

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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
Is vectorization worth the trouble with recent MATLAB?
Is vectorization worth it? Let me see. For example: Add 1 to every element of a vector. V = rand(1,1e6); % Which is itself high...

1 dag ago | 0

Answered
How to specify intervals of increasing, decreasing of a function in MATLAB
This can get fairly messy, if your function is carefully designed to cause you problems. For example, you may need to find a sin...

7 dagen ago | 1

Answered
Not exactly the exact answer using Symbolic Math Toolbox
Your problem stems from a common mistake. Whaen you write this: syms t f = sin(t); frms = sqrt(1/(2*pi)*int(f^2,t,[0 2*pi]))...

8 dagen ago | 1

Answered
How does the expfit function... functions
You may be confused. Well, let me say, almost certainly, you are confused. ;-) There is a difference between curve fitting, in ...

8 dagen ago | 0

Answered
No results are showing in the symbolic math computation
First, you need to recognize MATLAB is case sensitive. Your code does not run, instead, it fails in several places. I fixed it, ...

8 dagen ago | 0

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Answered
Solving ODE just for one time step
Then I fail to see the problem. You want only the solution at the end point. % A simple ODE. with y(0) == 1, the analytical s...

9 dagen ago | 0

Answered
Analyzing errors of a numerical Jacobian matrix of partial derivatives, as the finite-differencing step-size gets successively smaller,
I explained EXACTLY this in my last answer to your last question. Please read what I write and think about it. If you don't then...

9 dagen ago | 0

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Answered
How can I reduce the "method error" with my central-difference method, when estimating a Jacobian matrix of partial derivatives?
This is a complex question, with possibly no perfect answer. For example, suppose you have a Newton method, that employs a fini...

10 dagen ago | 3

Answered
Better package manager abstracted away from matlab versions
Why don't they have the perfect set of tools, exactly as you want them to have been written? Because MATLAB was designed to make...

12 dagen ago | 0

Answered
Generate n random numbers between 0.1 and 0.9 without repetition
There are always many ways to solve a problem. Here is mine: % generate the set of ALL possible combinations. There are not man...

14 dagen ago | 0

Answered
How to get real root of a function using fminbnd?
It sounds like you want to see the result: (-1)^(4/3) == 1 To do that, you want to use nthroot, by splitting the fraction...

15 dagen ago | 0

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Answered
solving numerically non-linear equation , code below does not work
What does not work? This is just a basic Newton-Raphson method. First, what are the functions for your test problem? x^2 + y...

16 dagen ago | 1

Answered
Find the range of duplicates in a sorted element
I'll create a longer vector, with a few duplicates. V0 = randi(8,[1,15]) V = sort(V0) Now you want to know where the dups liv...

16 dagen ago | 0

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Answered
What do you think of my numerical Jacobian, using the central-difference method?
What do we think of it? I'm sorry, but blech! Why? Don't number all of your variables! Don't create long lists of numbered var...

16 dagen ago | 1

Answered
Inverting an 8x8 symbolic matrix
What nobody ever seems to understand is that a symbolic inverse of a matrix like this grows exponentially in complexity. Many th...

19 dagen ago | 3

Answered
Is there any precomputation step on A'*(.)*A if matrix A is known, to speed up matrix computation A'*B_i*A in matlab with B_i denpends on the previous matrix B_{i-1}.
A is known and fixed, and apparently large, else you would not care about speed. The amount of memory on your laptop is irrelev...

20 dagen ago | 0

Answered
How to identify algorithm time complexity?
It is not at all trivial to determine the time complexity for SOME algorithms, at least not from merely knowing the method emplo...

21 dagen ago | 0

Answered
Where to Find a Dataset of High-Quality MATLAB Code for Training an LLM?
Looking at your question a second time, it is about MATLAB in a sense. in that you are looking for a repository of code to train...

24 dagen ago | 0

Answered
Logic Code required to be run in finite time
I think you misunderstand an important idea of computing. You NEVER want to use brute force on big problems. Those problems alwa...

27 dagen ago | 1

Answered
Find blocks iof non-zero values in Matrix
Sure. It should even be pretty easy. A = randi(200,[120,240]); % make up a matrix First, I'll convert it to binary, where a 1 ...

ongeveer een maand ago | 0

Answered
assigning values with []
@feynman feynman The funny thing is, I have at times wanted a syntax like you wrote to work in MATLAB, but it won't. We could p...

ongeveer een maand ago | 1

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Answered
How would I use a 2D array based on a topographical map to determine the steepest direction at each point?
You should be talking to your teacher, as these are questions they should be answering. But what does the gradient function do? ...

ongeveer een maand ago | 1

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Answered
Solving odes with ode45 and then checking fixed points for constant behavior,
How many times will you ask this question? Can you do better than 13-14 digits? No. Not in double precision. And a different O...

ongeveer een maand ago | 0

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Answered
I have a dataset of x and y coordinates in UTM units, and cumulative erosion or sedimentation in depth (m) units, I need the volume of erosion or accretion in cubic metres
Difficult, since you don't show the data. A picture of numbers is useless. A bigger problem is your data is surely not on some n...

ongeveer een maand ago | 0

Answered
In a (possibly directed) graph, is there a simple way to find all nodes reachable for a given node?
First, create a graph. M = eye(100) + triu(rand(100) < 0.035); spy(M) You will agree this matrix satisfies the requirements, ...

ongeveer een maand ago | 0

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Answered
Evaluating stability of fixed points in a system of differential equations,
First, there is nothing wrong with a loop! You know how to evaluate stability for each case. Just write the loop. Could you do s...

ongeveer een maand ago | 0

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Answered
linprog
Think about it. Do you need that constant at all? (NO.) LINPROG finds a location (in your case, in terms of x and y) that minim...

ongeveer een maand ago | 0

Answered
how to design digital filter
Are there free toolboxes to do filter design? You might find something on the file exchange, and what you find there comes at ...

ongeveer 2 maanden ago | 0

Answered
why does this not work?
It failed because datetime did not recognize that string as a list of distinct times. Just because you know what you want code t...

ongeveer 2 maanden ago | 3

Answered
Solving for a variable in an equation
First, you need to recognize there is NO analytical solution to your problem. So using solve means it will just toss and turn fo...

ongeveer 2 maanden ago | 0