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John D'Errico


Retired

Last seen: Today Active since 2006

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

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Answered
Questions about the isqnonlin function
This is NOT a problem with lsqnonlin, but in your understanding of determinants and why they are a bad thing to use. You misund...

ongeveer 4 uur ago | 2

Answered
Minimize distance between curves
This is a classic calibration problem of sorts. Lacking any data, I cannot really help you as much as I might want to. But I can...

1 dag ago | 0

Answered
Solve the system of three equations and three unknowns
The answer is actually pretty easy. First, you need to understand that those who are answering your question do not seem to appr...

1 dag ago | 1

Answered
Criteria for judging overfitting
If there were some clear and simple rule, then the code would be written to recognize that, and alert you of the problem. But th...

2 dagen ago | 0

Answered
Is there a reason why row vectors are default in Matlab?
It just is. Around 40 years ago, someone made a choice. The choice was fairly arbitrary. But they made it. And once made, that c...

3 dagen ago | 2

| accepted

Answered
How to sub sym to a number in a matrix
syms x y z M = [x-2,x+y,z^2] subs(M,[x,z],[1 3])

6 dagen ago | 0

Answered
Can the function "Taylor" process the input type "Function handle" directly?
Can taylor handle some completely general function handle? No. Why not? A Taylor series is easy to compute, in theory. The coef...

6 dagen ago | 0

| accepted

Answered
how to take numerical inverse integration?
This is technically called an inhomogeneous Fredholm integral equation, of the first kind. https://en.wikipedia.org/wiki/Fredho...

6 dagen ago | 0

| accepted

Answered
How can I find all n-bit semiprime numbers?
Ok, I'll give in. A reasonable question, with a reason to be asked. Given a valid reason for the question, I am actuually quite ...

7 dagen ago | 0

| accepted

Answered
generate a random number base on pdf function
First, is that the PDF of a random variable? If it was, the integral would be 1. syms x P_x = x/2 + 1/2; int(P_x,-1,1) And o...

7 dagen ago | 1

| accepted

Answered
Can we choose step size rule in fmincon?
If you could control the stepsize, then it would damage the convergence properties of a tool like fmincon. Sadly for you, this i...

8 dagen ago | 0

Answered
Describe a colormap in the legend of a plot
Hard to put it into a legend, since legend is not designed to do that. Far easier (one line of code) to just put a title above t...

8 dagen ago | 0

Answered
An example of a large matlab project
Look on the file exchange. You will see many such submissions. I have at least a few such, with at least one where I spent multi...

9 dagen ago | 0

| accepted

Answered
Rate of Change - Derivative of experimental data
If your data is smooth enough, then the direct gradient calls that Star shows are ok. The problem is, if there is any noise in y...

9 dagen ago | 0

Answered
I did not get any email for activation key. My recent purchase order is complete.
Answers is not customer support. Answers is a volunteer forum. we have no ability to help you. We have no access to any database...

9 dagen ago | 1

Answered
Putting one matrix a varying number of times along the diagonal of another matrix
A = rand(3); n = 50; Acell = repmat({sparse(A)},[1,n]); B = blkdiag(Acell{:}); spy(B) Note that I made A sparse in there, s...

9 dagen ago | 0

| accepted

Answered
How to use File exchange
It does not matter that you use a mac or not. Save the top level folder on your search path. So use pathtool or addpath. Then sa...

9 dagen ago | 0

Answered
Hello, I did a for loop but my friend told me it is not the correct matlab syntax. Can anyone help me the for loop is in the description below:
for xa=1; This is not a loop. It does nothing but assign the value 1 to the variable xa. NOTHING. No loop. Instead, it looks l...

9 dagen ago | 0

Answered
Output Symbolic Trig Math in Degrees
If you use cos and sin, terms like this are meaningless, if the 90 is a number in degrees. Well, let me just say you will get me...

11 dagen ago | 0

Answered
out of memory error
Um, 1e20 rows? Seriously? Do you have that much memory? Clearly not, since your computer is throwing up at an 1e8 by 27 array. E...

12 dagen ago | 3

Answered
How to numerically integrate the planar equations of motion?
You need to learn how to write a function handle. What you wrote was incorrect syntax. Do you see the spare comma, AFTER the par...

12 dagen ago | 1

Answered
Converting to scientific notation in matlab
We are not a "team". We are just a number of people who act as complete volunteers, individually. You cannot "represent" it tha...

12 dagen ago | 0

| accepted

Answered
Why the result in curve fitting tool shows a different graph in plot?
@Hao Tu (This is only a followup, and since you already understand the issue, merely a clarification to Steven's accurate answe...

13 dagen ago | 1

Answered
What is the difference between backward slash vs forward slash in MATLAB?
BOTH of them are linear algebraic solutions. Where matrices are involved, they solve subtly different problems. A\b solves the ...

13 dagen ago | 2

Answered
Fmincon makes an extremely big jump in parameter search
I think you do not understand how an optimization tool works. Those first calls to your objective are there to differentiate it...

13 dagen ago | 0

Answered
How to smoothen a plot?
Simple. Delete the points in the beginning of the curve that give you the spikes. WTP? They will be easy enough to spot, as they...

13 dagen ago | 0

Answered
How to write code for Assignment problem using GA matlab tool.
Does GA allow you to specify that some variables are integer? (Yes.) Does GA allow you to specify lower and upper bound limits ...

14 dagen ago | 0

Answered
Solving a System of Trig Equations
If the only unknown is theta1, then what is y? If you actually have a value for y, then you have two equations in one unknown v...

14 dagen ago | 0

Answered
Solve Equation and Plot it
Easy peasy. Essentially one line of code once you define the various constants. syms f_1 f_2 alpha = 0.4207; skalar = 4.5375;...

15 dagen ago | 0

Answered
Declrarion of an array using tilde (~). what is the correct way of using it, because my code prompts me incorrect use of tilde.
This is a test: if i == D(k) It is the correct way to use == because == is a comparison operator. However, this other line is...

16 dagen ago | 1

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