# 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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**Feeds**

Is there a premade file regarding a verification test to see if there is any issues with the installation?

Is there anything that will test every line of code in MATLAB? Every toolbox you have purchased? No. Not that is given out to yo...

ungefär 9 timmar ago | 0

I have a question relate to Gauss seidel method

Updating the vector x (small x) and then looking to see if the vector X (capital X) is converging seems like a bad idea. You did...

ungefär 16 timmar ago | 0

integral using "int" function

Not everything you write down will have a simple, algebraic solution. As much as people seem to think they are, computers are no...

en dag ago | 0

f(x) = x^2/3(3-x^2)(x-4). How do I enter this function in MATLAB?

How do you enter it? You already did exactly that, at least in symbolic form. syms x real % f= input('Enter the function f(x):...

2 dagar ago | 0

Very large output numbers

syms Kc s X = (6982830709666455*Kc*s)/140737488355328 vpa(X,10) So here, 10 digits shown.

4 dagar ago | 0

atan2 does not accept complex numbers as input

It seems the answers provided so far are missing the point. If we want to see a 4 quadrant atan2 version, that works for complex...

4 dagar ago | 1

| accepted

Generalised solution to a n-order system of equations

(Edited to fix my error in extrapolating your equation system. I had not seen at first you were essentially adding two terms to ...

5 dagar ago | 2

I need to write a code to find numbers divisible by 7 and multiples of 5 from 1500:2700. How do I preallocate line 4 for speed and is my code the most efficient way to solve

Lol. A huge amount of traffic on this from last night when I looked in. But you did write code. So how would I solve the problem...

5 dagar ago | 0

Best computer specifications for fast Matlab numerical simulations/integrations?

Something I've said before, when this same question gets asked... If you will do heavy computations for lengthy periods of time...

5 dagar ago | 1

Patenting a Matlab script

Adding to what @Steven Lord has said, it is not that easy to do. And it is may even be the wrong path to take too. (Even though ...

5 dagar ago | 0

Why is it when I am adding a number to array, the single number overrides array

E=10.3*10^6; %psi Fty=68000; %psi Ftu=76000; %psi fnl=linspace(0,Ftu,250); e0=0.09; epu=e0-(Ftu/E); nt=log(epu/.002)/log(F...

7 dagar ago | 1

How to solve for the maximum or minimum value of a symbolic function

You need to understand that not ALL equations you can write down have an analytical solution. In fact, it is trivial to formulat...

8 dagar ago | 0

why use 0.008856 in Lab color space?

Its been a million years since I looked at those equations. But it seems likely to be almost trivial. They chose a point where t...

9 dagar ago | 2

Get awnsers with infinity using matlab solver

No. I'm sorry, but you are wrong. You think of infinity as a number. It is not. Infinity is greater than any number. And, yes, M...

11 dagar ago | 0

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Why does this function appear noisy?

Do you understand how floating point arithmetic works? That you only have a finite number of digits, and that when you subtract ...

11 dagar ago | 0

| accepted

Contour plot of cubic interpolation with set number of contour levels

Simple enough. You should have looked at the handle returned by plot. Though I guess it helps if you know what to look for. ;-) ...

11 dagar ago | 2

| accepted

how to create function for below objective function.

Your objective function has three unknown variables in it, so z1, z2, and w. But an optimizer MUST have it as a vector of length...

12 dagar ago | 0

Why does fitlm say my "design matrix is rank deficient to within machine precision" despite my design matrix being full rank?

Funny. I was sure within a second of reading your question what you had done wrong. And I think you will probably say, Oh. Yeah....

12 dagar ago | 0

Find the m of nonlinear equation without initial input m. Please help me, my supervisor ask me to find m without input initial m from right. I know this is nonlinear equation.

Not homework, but barely any effort made. Sigh. This is apparently your job. You need to start learning MATLAB. sigma = [ 137....

13 dagar ago | 0

Global optimization strategy with local interpolation

You want to use a high dimensional local interpolation method, so in 6 dimensions. Since you are using it to find a local optimu...

14 dagar ago | 0

Help explain interpolated surface coloring

Without looking deeply into the method used to interpolate, I can't absolutely know what their code does. However, I do deeply u...

17 dagar ago | 1

| accepted

Solve more complex problems in matlab

Can you just throw it at solve, and hope solve can figure out what is your question? Probably not. A tool like solve is not that...

19 dagar ago | 0

Solve equation with multiple variables

Let me explain SOME of the the mathematics here. First, you have 4 equations, in 4 unknowns. Typically, that means there is one...

21 dagar ago | 0

If I deactivate my llicense on one computer to try Matlab on my new computer, can I reactivate the old computer Matlab if the new computer Matlab does not work?

Well, yes. You can go back, even though we learned long ago that "You can't go home again", Thomas Wolfe may have fed us a littl...

21 dagar ago | 1

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Plotting random number in a line

What is it that you want then? A plot requires TWO axes, TWO variables to be plotted, typically we might plot x versus y. My fi...

22 dagar ago | 0

How can I plot a hyperbola?

Just for kicks, we can do a little algebra. Start with the original form. syms x y eqn = 0.4829 == sqrt((95-x)^2-(0-y)^2)-sqrt...

22 dagar ago | 0

How reduce data from 3917x2 to 1868x2 without change the entire of graph?

Just take every other data point, if you just want to roughly reduce the size. But you say you want a specific length. So then y...

24 dagar ago | 0

| accepted

I want to start a youtube channel where i develop flight control algorithms. Which matlab license do i need?

You definitely want to contact support, as only they can answer your question. I am not a lawyer. However, it seems if you are ...

27 dagar ago | 1

How to filter out the noisy portion of contourf plot?

One basic rule that always applies to things like this. You DON'T want to smooth contours after you have found them. You can't t...

28 dagar ago | 0

How to plot one curve and change color according to value

As ifs often the case, I am far too late to the party. :) But there are often many ways to solve a problem, so I like to be able...

29 dagar ago | 1