# John D'Errico

### Retired

Last seen: 1 día hace Con actividad desde 2006

Followers: 11   Following: 0

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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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):...

alrededor de 9 horas hace | 0

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

1 día hace | 0

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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...

1 día hace | 1

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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 ...

3 días hace | 2

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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...

3 días hace | 0

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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...

3 días hace | 1

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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 ...

3 días hace | 0

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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...

5 días hace | 1

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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...

6 días hace | 0

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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...

7 días hace | 2

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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...

9 días hace | 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 ...

9 días hace | 0

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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. ;-) ...

9 días hace | 2

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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...

10 días hace | 0

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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....

10 días hace | 0

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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....

11 días hace | 0

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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...

12 días hace | 0

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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...

15 días hace | 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...

17 días hace | 0

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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...

19 días hace | 0

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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...

19 días hace | 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...

20 días hace | 0

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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...

20 días hace | 0

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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...

22 días hace | 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 ...

25 días hace | 1

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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...

26 días hace | 0

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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...

27 días hace | 1

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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 .....

28 días hace | 0

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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...

29 días hace | 1

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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 ...

29 días hace | 0