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John D'Errico


Last seen: 1 day ago

Retired

5,149 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
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...

7 hours 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 ...

22 hours 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...

1 day ago | 0

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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...

2 days 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, ...

2 days 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...

2 days 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 ...

3 days 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...

3 days 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...

3 days 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...

3 days 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 ...

4 days 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...

4 days 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...

4 days 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...

5 days 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

5 days ago | 1

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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 ...

5 days ago | 0

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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...

5 days 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 ...

5 days ago | 3

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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...

6 days 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...

7 days 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...

7 days 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...

7 days ago | 1

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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...

7 days 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 =...

8 days ago | 1

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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...

9 days ago | 1

Answered
calculate tension by raphson newton in matlab
You have indicated these coefficients, although I worry there may be issues, because of the use of lower versus upper case W, et...

9 days ago | 0

Answered
Interpolating n-dimensional functions
First, IF you have a complete gridded lattice, then you don't want to use griddatan. That is DEFINITELY a BAD idea. Why? Because...

9 days ago | 1

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Answered
What am I missing here?
Thank you. That makes it much easier for someone to offer you help. Now I'll be willing to look at the problem you had. It loo...

10 days ago | 1

Answered
How to extrapolate a contour plot?
Let me see. You have data in only 25% of the region of interest. Now you want to extrapolate that data into a region that compri...

11 days ago | 0

Answered
To solve non-linear equation by inversion notion
STOP. Is this nonlinear? Or is it linear? A*X = b is still LINEAR, even if the array is not square. Even in the linear case, t...

11 days ago | 0

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