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John D'Errico


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Retired

5,456 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 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 ...

8 hours 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...

14 hours 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 ...

15 hours 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 days 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 days 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 days 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...

3 days 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, ...

3 days 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...

3 days 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...

4 days 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 days 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...

5 days 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...

5 days 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...

5 days 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...

5 days 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 days 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 days 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 days 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...

6 days 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 days 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 ...

7 days ago | 0

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

7 days ago | 1

Answered
excluding a small combinations from a combination?
There are not that many combinations that include the subset [2 4 6] out of nchoosek(1:10,4). This means the oversampling will n...

7 days ago | 0

Answered
How to plot a complex function in matlab like : f(z)=sin(z)?
The problem is, if z is a complex variable, then so is the extension of sin(z) into the complex plane. For example... sin(1 + i...

8 days ago | 1

Answered
Integration of a function
It can be confusing at times I have seen for newcomers to know which tools apply where, because we have symbolic tools and numer...

8 days ago | 0

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Answered
what does this line do
It does nothing on its own. A single line of code has little meaning, out of context. What does it do? It sets some elements o...

8 days ago | 0

Answered
Matlab solver for natural log equation
Does a solution near(er) to zero exist? PLOT IT!!!!!! syms x f = (-27109/x)-0.95*log(x)+25.18 - log(0.5); fplot(f,[10,1000]) ...

8 days ago | 0

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Answered
Is NaN ok here?
Sure. It does not bother me. Why does it bother you? B = [1.66000000e-01 6.60000000e-02 1.40000000e-02 3.90000000e-02 1.4000000...

9 days ago | 0

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Answered
Gaussian Quadrature Error Help
I think you misiunderstand Gaussian quadrature. You claim to have 4 points. WRONG. You have TWO points in x, and TWO in y, the...

10 days ago | 1

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Answered
Tic, Toc Behavior
Using tic and toc to masure any time is a bad idea. Using tic and toc to masure any time is a bad idea. Using tic and toc to m...

10 days ago | 1

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