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John D'Errico


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Retired

5 154 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 apply a fit on this shape?
What does it mean to "fit" it to you? What will you do with that fit? The data is not a function, just a set of points, that hap...

environ 9 heures ago | 0

| accepted

Answered
Detect collinear points in a 3d points cloud
I think your problem is in the breath of the search. If you make this a problem of finding sets of three points, then you have t...

environ 10 heures ago | 1

| accepted

Answered
Solution to Ax-b
Ok. If your matrix is not full rank, then the answer is easy, though it wil probably not be the answer you want to see. Really, ...

1 jour ago | 0

Answered
Help with increased precision.
NO. You don't use vpa. No need to do that, and in fact, vpa would be the wrong tool to use anyway. This works fine though. a =...

1 jour ago | 0

Answered
Removing replication in matlab
But the string, after you remove the replicates will always be identically the same, just alternating 0's and 1's. If the first ...

1 jour ago | 1

Answered
fsolve cant find a solution for some points
It is actually pretty simple to solve this. Remember that fsolve uses a basic algorithm. Start the problem out in the wrong plac...

2 jours ago | 2

Answered
lower and upper index in sorted vector
Please don't post pictures of numbers. That makes it more difficult to help you, to answer your question. Why would you make it ...

2 jours ago | 0

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Answered
When does randomness enter a shuffled "deck" of coin tosses.
I put together this simple script. In it you will find perhaps the most efficient scheme for a riffle shuffle that I know of, si...

3 jours ago | 0

| accepted

Answered
command window does not recognize the functions in editor
I think you need to learn about the MATLAB search path. While the editor can save a file anywhere you tell it to, when executin...

3 jours ago | 0

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Answered
Binary Quadratic Programming Relaxation
While you could just use a tool like quadprog with continuous varibles in the interval [0,1], then round the result at the end, ...

3 jours ago | 0

Answered
Tools used for Sparse Matrix Efficiency
Whoever gave you that advice, about never building a sparse matrix one element at a time must have been very knowledgable, as it...

4 jours ago | 1

Answered
Fibonacci even numbers. Code doesn't work for large numbers
Why are you surprised? log2(fibonacci(100)) ans = 68.263 You cannot represent an integer exactly in double precision ...

4 jours ago | 3

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Answered
Block Tri-diagonal Matrix
It may be your lucky day. Just download my blktridiag code from the file exchange. https://www.mathworks.com/matlabcentral/file...

4 jours ago | 0

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Answered
i=1, 2, 3,,, However, when (a-i)> 0 is calculated.
Or, with no loop at all, and no test required. Just i = 1:a-1; station(i+2) = (4-(4-i))*N; This will define the entire vector...

4 jours ago | 0

Answered
How to measure the correct circularity??
It would not be unusual for that measure to exceeds 1. For example, given a circle, we would have a perimeter of 2*pi*r. So perm...

5 jours ago | 0

Answered
Fitting an exponential using nlinfit
Most of the code you posted is meaningless, since you save only the variables whos Name Size Bytes ...

5 jours ago | 0

Answered
random integer condition selection
You want to generate a random number of random numbers? With an additional constraint that all are greater than 0.5? This is far...

5 jours ago | 1

Answered
[Solved] Upsampling multidimensional array with interpn
That is NOT a 5 dimensional array. While you may THINK of it as a set of points that live in 5 dimensions, it is NOT a 5-d arra...

6 jours ago | 0

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Answered
Plotting a function (Horner Schema)
While polynomic psychological analysis seems well beyond my talents, Horner's rule is pretty easy. :) And since you made a credi...

6 jours ago | 1

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Answered
Matlab says the matrix is not symmetric
D = rand(100); D = (D + D.')/2; issymmetric(D) ans = logical 1

6 jours ago | 1

| accepted

Answered
how can i create a circle with a face color changing radially
[x,y] = meshgrid(linspace(-3,3)); z = exp(-x.^2 - y.^2); H = pcolor(z); H.LineStyle = 'none'; colormap(jet) axis equal ...

6 jours ago | 0

| accepted

Answered
Fit a curve on scatter data (main behaviuor)
You "want" the green line. I want the Buffalo Bills to win the Super bowl. Probably not gonna happen in either case. ;-) You wa...

6 jours ago | 0

Answered
How can I understand why certain sets of random variates lead to the warning message "Unable to meet integration tolerances without reducing the step size below the smallest value allowed (1.136868e-13) at time t=51"?
Nobody yet wants to explain it? The standard reason for this error is because you are creating a problem that is too stiff for ...

6 jours ago | 3

| accepted

Answered
What am I getting wrong with trying to create a sphere mesh using a golden spiral?
So you are not looking for a mesh at all, just a uniform sampling? Simplest might be to use a random sampling, with a twist. Tha...

7 jours ago | 0

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Answered
Why do I get a graph that is symmetrical based on x=-2 when I draw a graph of y1=4*log((x+2))?
It is not clear what you wanted to plot. However, I think you misunderstand. It is still possible to evaluate the log of a nega...

8 jours ago | 0

Answered
Tabulated Gauss-Kronrod weights and abscissae
I might presume the mp indicates some variation of the multi-precision toolbox. An old free version has been on the File Exchang...

8 jours ago | 0

Answered
Solving symbolic trig equation
You can NEVER solve for those variables, at least as the equations are written. First of all, z never even appears. But since y...

9 jours ago | 1

| accepted

Answered
How to get the value of an extra variable with fsolve
The simple trick is to use the output arguments from a function. Change your function header to look like this: function [F,r...

9 jours ago | 0

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Answered
Find the intersection points between two data sets
Finding the intersection point is easy enough. [intx,inty] = intersections(data1(:,1),data1(:,2),data2(:,1),data2(:,2)) intx =...

9 jours ago | 1

| accepted

Answered
numerical solution of a system of ODE which is not in standard form
Your question seems to be one of solving a system of ODEs with a mass matrix. For example in the help for ODE45, we see this opt...

10 jours ago | 1

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