# John D'Errico

### Retired

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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**Content Feed**

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...

ongeveer 2 uur ago | 1

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...

ongeveer 6 uur ago | 0

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...

1 dag ago | 0

| accepted

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...

1 dag ago | 2

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...

1 dag ago | 0

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...

1 dag ago | 0

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...

2 dagen ago | 0

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...

3 dagen ago | 0

| accepted

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...

3 dagen ago | 0

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...

4 dagen ago | 1

| accepted

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...

4 dagen ago | 1

| accepted

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...

5 dagen ago | 0

| accepted

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...

5 dagen ago | 0

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...

6 dagen ago | 0

| accepted

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 ...

6 dagen ago | 1

| accepted

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...

7 dagen ago | 0

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...

7 dagen ago | 0

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...

8 dagen ago | 0

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 ...

8 dagen ago | 0

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 ...

9 dagen ago | 0

Fastest possible prime number detection without using break or return

You did write working code to find primes. Well done there. But the fastest code? Without breaks, or returns. Easy peasy. Write...

10 dagen ago | 0

I am new to matlab and I am trying to get prime numbers

But these loops will not result in prime numbers. (As you have found.) I think you are trying to do a simple sieve, or something...

10 dagen ago | 2

| accepted

How can i calculate the area under two curves that intersect?

1. Subtract the two curves. 2. Take the absolute value of the difference. 3. Compute the integral. Note that you ...

10 dagen ago | 1

the arc using the chord

Your question is far too general, too vague to have an answer. There are infinitely many "arcs" that will pass through two poin...

10 dagen ago | 0

MIL SIL equivalence check.

A literally impossible question to answer. Both far too broad, too vague, and yet extremely specific. It is not even clear what ...

10 dagen ago | 0

How do I create a variable H which contains the product of 5 and the values of B in the 1st and 9th rows, and the 1st and 2nd column.

Ok, first, you do understand how to extract the elements from B. Good there. I think maybe the question wording is confusing you...

11 dagen ago | 1

| accepted

Is this a logical Error in Matlab ? exp (pi*i*6) = 1.000000000000000 - 0.000000000000001i. WHY an i component ?, should just be 1

Remember that pi in MATLAB is not truly pi, any more than pi is 3.14, or even 3.14159. pi is a transcendental number. There are ...

11 dagen ago | 2

| accepted

How can MATLAB's extensive suite of functions for data analysis and visualization be utilized to import, process, and analyze simulation data, including performing frequency a

Um, learn MATLAB. That means you need to learn how to read the help, the documentation for those tools. Start by doing the bas...

11 dagen ago | 0

Symbolic integration has 3 solutions based on integration variable range, how to extract one of these?

Or do this: syms r umax Radius mom_2 = int((umax*(1-r/Radius)^(1/7))^2*2*pi*r,r,0,Radius) subs(mom_2,Radius,1) Note that it ...

13 dagen ago | 0

How do I find the most stable N consecutive numbers?

The mean difference? What is that exactly? In terms of mathematics? Are you looking for the 50 element consecutive subset with ...

13 dagen ago | 0