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John D'Errico


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Retired

5.464 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
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...

22 minuti ago | 0

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...

circa un'ora 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...

circa 4 ore 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...

circa 5 ore 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 ...

circa 8 ore 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...

circa 8 ore 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...

circa 10 ore 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...

circa 11 ore 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 ...

1 giorno 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...

1 giorno 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 ...

1 giorno 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=...

3 giorni ago | 1

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...

3 giorni 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...

3 giorni 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...

4 giorni 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, ...

4 giorni 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...

4 giorni ago | 0

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...

5 giorni 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...

5 giorni ago | 1

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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...

6 giorni ago | 0

| accepted

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...

6 giorni ago | 0

Answered
How to draw a 3D circle that is tangent to two lines
First, if the lines are in the same plane, then you can pretend this is a problem in 2-dimensions. You can always rotate everyth...

6 giorni ago | 0

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Answered
Determinant of a unitary matrix
Gosh. I wonder, if there were really much better ways to compute the determinant, they might have used it? ;-) There are no spe...

6 giorni ago | 0

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Answered
How to remove duplicates from a matrix without using unique?
How could you use the output of a sort to help? Why not make an effort?

6 giorni ago | 1

Answered
Can anyone tell what is this line doing
You asked again, why you cannot use f(1,3), instead of f(1,2). LOOK CAREFULLY AT WHAT YOU HAVE. TAKE IT ONE STEP AT A TIME. f...

6 giorni ago | 0

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Answered
Create Random Points in Elliptical Belt
If you already know how to generate random points uniformly over an elliptical region, then you already have the simple answer. ...

6 giorni ago | 0

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Answered
Exponential distributed random values
You need to do that since your exponential rate parameter varies. If it were constant, this would not be necessary. The first a...

7 giorni ago | 0

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Answered
How can I solve the determinant of large-sized symbolic matrix: det(A)=0?
First, you don't want to solve for a zero determinant! Period. This will never be a well-posed problem, simply because we can tr...

7 giorni ago | 0

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Answered
Composite Simpson's 1/3 rule code error
Tell me, what is fx? fx is NOT a function. It is a scalar, vector, or array. Whatever x was, fx is the same thing. If it NOT a ...

8 giorni ago | 0

Answered
Creating a Matrix of random numbers
randi([0 1],20)*2 - 1

8 giorni ago | 1

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