# 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**

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...

1 jour il y a | 0

| A accepté

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 ...

1 jour il y a | 0

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. ;-) ...

2 jours il y a | 2

| A accepté

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...

2 jours il y a | 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....

3 jours il y a | 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....

3 jours il y a | 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...

4 jours il y a | 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...

8 jours il y a | 1

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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...

10 jours il y a | 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...

11 jours il y a | 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...

12 jours il y a | 1

| A accepté

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...

13 jours il y a | 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...

13 jours il y a | 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...

15 jours il y a | 0

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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 ...

17 jours il y a | 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...

18 jours il y a | 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...

20 jours il y a | 1

why does this line of code give error- disp("The density of " + element ... + "is" + density). When i press the 'enter ' key after the 3 dots and rerun, it works.

Do this instead: disp("The Density of " + element + " is " + density) What did you write? disp("The Density of " + element .....

20 jours il y a | 0

How to fit power-law to each column of data arranged in a table?

Why should it work? I see these lines: [fitresult, gof] = fit( xData, yData, ft, opts ); % Goodnes of the Fit R^2 result...

21 jours il y a | 1

To RESHAPE number of elements must not change

How do you fix it? Make sure you know what the size of your array is, before doing a reshape. This way when you do that reshape ...

22 jours il y a | 0

hi, find the value of x theoretically?

Do you assume that every expression you can write down has an analytical, neatly written algebraic solution? Surely not. Start ...

23 jours il y a | 1

Is a matrix with a condition number of 1e20 definitely more ill-conditioned than a matrix with a condition number of 1e19？

NO. There is effectively no significant difference between the two. At that point, you are into what are essentially random bit ...

24 jours il y a | 1

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How to generate vector with non-linear spacing?

It sounds like you want a deterministic, non-random set of points. You can use the inverse gaiussian CDF to do what you want. a...

24 jours il y a | 2

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Ordering multivariate polynomials by increasing higher order terms

The problem is, the symbolic toolbox does not use the term sequence you personally prefer. In fact, you can't control the sequen...

25 jours il y a | 0

I'm doing an project in matlab software and my data set having more than 1 lakh images so can you prefer any best laptop for this processing in i7

I think you do not understand. Moving from an i5 to an i7 will improve things. Multiple cores, lots of memory will be nice, even...

27 jours il y a | 0

Multivariate regression for constrained dependent variables

Sorry. You CANNOT insure that y1+y2 == 1, EXACTLY. At least not if there is any noise in your data. All you can do is to use it...

28 jours il y a | 0

Using Matlab Runge Kutta Routine

"IT WON'T GO PAST THE FIRST INCREMENT". Lol. Exactly what do you think this does in the very beginning of the loop? for count ...

29 jours il y a | 0

Unable to resolve the warning on ill conditioned Jacobian

A not uncommon misunderstanding about modeling. First, look carefully at your data. M = importdata('datai2j3.txt'); x = M(:,1...

environ un mois il y a | 0

volume of set of points in 3d space with gap

Is there any way you can make the convex hull adequately represent a region that is not in fact convex? Of course not! You have...

environ un mois il y a | 0

Problems by calculating zero points of a cubic function

Or, you can use analytical tools. syms x a f = -2*x^3 + x^2 + 0.5*x -8; % Remember to use * to multiply fa = f + a; Before y...

environ un mois il y a | 0