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John D'Errico


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Retired

5.473 total contributions since 2006

(Don't contact me. I won't answer questions.) A retired mathematician, numerical animalist, woodworker, bridge player.

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Answered
How to make Triu in reverse axis for triangular matrices ?
Are you asking to do no more than this? A = magic(6) A = flip(tril(flip(A))) That is a simple way to do it. There would be ot...

alrededor de 17 horas ago | 0

| accepted

Answered
Zone identification on curve
Should a function automatically identify a staircase function? No. That can be quite difficult, especially if your staircase is,...

2 días ago | 1

Answered
How can I put the outputs of for loop into a matrix?
First, don't use loops at all. For example, with n==3... n = 3; ind = 1:n; a = ind.'*5/n + ind*8/n Since this is probably ho...

3 días ago | 0

| accepted

Answered
Why is it that Matlab has so many data types?
So? If you don't need them, then something you don't use has no impact on you. MATLAB is a complex, powerful language, that can ...

3 días ago | 0

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Answered
Some difference between MatLab and VS calculation
Which is more correct? Neither is correct in the bolded digits you post. In fact, the digit preceding that is also incorrect, in...

3 días ago | 0

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Answered
how to plot verticle lines?
Plot two points, connected by a line. Both points will have the same value for x. You can choose the start and end point in y to...

3 días ago | 0

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Answered
Finding min and max of an element without using builtin function
You are missing the point here. This is an exercise. The intent is for you to find a solution that does not use max or min. Doe...

3 días ago | 1

Answered
3D Printer Costs
Honestly, this is something more easily written using a spreadsheet. They are perfect for such an application. Fill out the hal...

3 días ago | 0

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Answered
The fix(x) command does not work
Fix does work. You need to understand what you asked it to do. A = [4 3 2 1;2 5 6 2;0 0 1 3;-1 -2 9 8]; format long g B = inv...

4 días ago | 0

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Answered
Solve: Unable to find explicit solution.
I spent 20 minutes writing a detailed answer to your question, only to find you appeared to have deleted the question. Now it is...

4 días ago | 0

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Answered
I'm trying to plot this equation, if anyone can help
If no value is supplied for a, then what will you plot? Perhaps you might do this: a = 0.25:0.25:2; L = cell(size(a)); for i...

4 días ago | 0

Answered
How to hinder ongoing spamming II?
I've been deleting the posts as I see them. First, get any new account ids, so I can send that info to our admin, so he can di...

4 días ago | 0

Answered
lsqcurvefit bad fitting results
Honestly, I would NOT solve it like that. Not even remotely so. Using lsqcurvefit for this just seems fraught with problems. Wh...

4 días ago | 0

Answered
understanding and converting two matlab function to c++/c code
You could read the documentation for thse functions. In there, you will find a complete explanation of what those codes do. The ...

4 días ago | 0

Answered
User defined FFT function parameter not recognized
How did you call the function? When you get an error, report the ENTIRE error message, everyting in red. This lets us know how y...

4 días ago | 1

Answered
What is the difference between Double 1.0000 and Double 1 ?
If you see the number in MATLAB displayyed as 1.000 in the command window, then almost always you don't have the number 1. Inste...

4 días ago | 0

Answered
How to fit this signal to x axis at y=0 using polyfit/polyval?
This is just another case of someone not understanding how polynomials work or behave. Seriously, to fit a polynomial to that d...

4 días ago | 0

Answered
How can I fit an exponential curve?
x = [35.668 34.448 33.317 30.357 27.598]; y = [180 504 1260 10300 80900]; plot(x,y,'o-') First, recognize you have only 5 ...

5 días ago | 0

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Answered
Calculation of two less than equal
You want to solve for a scalar m such that the inequalities are always true? Regardless, does a solution ever exist? Note that u...

5 días ago | 1

Answered
i am new. i need help. kindly answer.
If this is homework? It very possibly is, because there are relatively few good reasons I can think of to solve any integration ...

5 días ago | 2

Answered
Euler's Method and exact solution plot
Sorry, but your code is wrong (so is your exact solution.) Why? Look at what you wrote. h=0.05; % time step t=...

7 días ago | 1

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Answered
MATLAB cannot integrate trigonometry in the form of degree
I think you do not understand integration, IF your expectation really is the two should be the same. That is, you think the inte...

7 días ago | 1

Answered
how to plot a function symbolically?
You have the relationship z(r) = H - C^2/(2*g*r^2) If H and C are not known, with g fixed at 9.8, then they make this in...

7 días ago | 0

Answered
Query regarding finding the index which will give 90% of the total area under the curve
No. You found some approximations of the area, using either trapz or polyarea. In both cases, they produced what is a trapezoida...

7 días ago | 1

Answered
fit these curves and what type of fit they are?
Your data is noisy. There is NO specific function that describes the data. It is NOT truly linear. It is NOT truly exponential, ...

7 días ago | 0

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Answered
I want to set a range of variable to three or four places of decimals
Are you asking to create a variable that only carries 3 or 4 digits of precision? You can't choose to set an arbitrary precision...

7 días ago | 0

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Answered
atan2 not consisent
What you don't understand is that just because MATLAB displays a number represented to 15 digits, does not mean it is EXACTLY th...

9 días ago | 0

Answered
Error using ==> asind Argument should be real.
So what is the problem? It seems the error message states exactly what happened, and why MATLAB sees a problem. Honestly, it ju...

9 días ago | 1

| accepted

Answered
how do I right x^2 in MATLAB
Is x a scalar? If so, then you write it as x^2. Is x a vector? Then, assuming you want to perform an element-wise squaring, yo...

10 días ago | 0

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Answered
4D Interpolation scattered Data
Sorry, but you cannot use tools like griddata or scatteredInterpolant to interpolate non-single valued relations. It seems all y...

10 días ago | 0

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