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# John D'Errico

### Retired

5.047 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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Natural Cubic Spline boundary conditions
The name "natural" boundary essentially conditions on a spline refer to the use of calculus of variations in the derivation of t...

alrededor de 2 horas ago | 0

How to predict the function in two variables?
Actually, probably not that. It appears there are three curves, each representing f(x), at ONE specific value of t. There are th...

alrededor de 5 horas ago | 0

Solve linear least square problems with non-linear constraints
Someone might tell you to use fmincon. And they would be right, in a sense. But they would be missing an important point. https...

1 día ago | 0

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convert data to a function using polyfit
This is almost what would normally be called a broken stick regression, except the joints between the linear segments are curves...

1 día ago | 1

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Inverted signs using eig function... again
I've posted a new version of eigenshuffle to handle generalized eigenvalues. https://www.mathworks.com/matlabcentral/fileexchan...

1 día ago | 0

Submitted

Eigenshuffle
Consistently sorted eigenvalue and eigenvector sequences

What are the commands for...
Column space basis orthogonal representations are obtained in MATLAB using either null or orth. In fact, they work regardless of...

3 días ago | 0

how to fit a function on my dara
When you get an error, don't just tell us you got an error. Paste in the complete error text. At least, you showed a picture of ...

3 días ago | 0

Is cputime a linear function of the number of for-loops?
This is a complicated question, in the sense that you need to understand the mathematics FIRST. And I think you do not understan...

4 días ago | 0

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Issue with gammainc(x,a) for small x and larger a
Sadly, you are limited in that no matter how hard you try, you will not be able to compute it in double precision when it is tha...

4 días ago | 1

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interpolation between two fixed points
I'd never have guessed what the quetion was from the initial question as written. But the answer is to use discretize. You hav...

5 días ago | 0

How to realize Riemann Siegel Theta Function with MATLAB？
You start by writing the formula for it. That can be found on virtually the first line in this link. https://en.wikipedia.org/w...

6 días ago | 1

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Find Beta in Half Rectifier on matlab
WHAT DID YOU TRY? If nothing, why not? Did you try using the symbolic toolbox? It looks like solve won't give an analytical res...

6 días ago | 1

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Why I am unable to recreate curve fitting equation?
I had to play with this for a while, because my first assumption was that you were using the wrong coefficients. In fact, while ...

6 días ago | 0

Integral from sin(x+y) from dx shows wierd result
Computers don't really care that YOU think it looks wierd. The fact is, that form for the integral is correct, just as much so a...

6 días ago | 2

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Howto Replace Specified and Non-Specified Elements in Matrix with Strings
You cannot do so. Sort of. Ok, well, you can. sort of. A double precision matrix in MATLAB is a rectangular array that contains...

7 días ago | 1

Solving an Incomplete Matrix such that A*transpose(A) = eye(n)
There exist NO such values for a,b,c such that A*A' == eye(3). Look carefully at A*A'. vpa(A*A') ans = [ ...

7 días ago | 2

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Problem of color interpolation of surf plot
This is an interpolation artifact. The cause is a pretty simple one. Fixing it is slightly less trivial, because you need to und...

8 días ago | 0

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How to extrapolate the plot of continuous data points so as to extend the region of plot
“In the space of one hundred and seventy six years the Lower Mississippi has shortened itself two hundred and forty-two miles. T...

8 días ago | 0

How do I create a polygon with n sides with only 90 degree or 270 degree internal angles?
I guess I don't really see the problem. And I don't really see where you are going with this, but... Start with a library of ev...

8 días ago | 0

Golden Section Search algorithm, golden number why is 0.381
I think you need to spend some time in class listening, lol. Or, maybe your instructor did not explain this. It is very possible...

9 días ago | 2

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"temp" was previously used as a variable, conflicting with its use here as the name of a function or command.
The MATLAB language does not include this syntax temp += 26 Just because it works in some other language, does not make it va...

9 días ago | 0

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"Scattered Interpolant" produces invalid values
I can shed light on your problem. What you think of as extrapolation is different from the way scatteredInterpolant sees the con...

9 días ago | 1

FZERO requires at least two input arguments
However you got the code you wrote, much of it is not valid syntax in MATLAB. This line, for example: fzero ltol = 10^-14; mid...

10 días ago | 0

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Contour plot ignores a set of data points
I've moved what was a comment into an answer, then added a bit... A very simple example of what I described is shown here: px ...

10 días ago | 1

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solve integral using ode45 (by derivative)
While what Ameer wrote looks like it will work, it still uses the dreaded & disallowed integral function. I'm adding this answer...

10 días ago | 1

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How can I PERMANENTLY change the path each time MATLAB is opened?
help savepath As well, if you were setting the path using pathtool, there is an option to SAVE the path. This leaves only the ...

11 días ago | 0

No. the code gives the correct answer in terms of what you wrote. That the code you wrote does not solve the problem you want to...

11 días ago | 2

how to know if two lines are intersected ?
Just find the point where the lines are at their closest approach. If the point of closest approach is zero, they intersect. Gi...

11 días ago | 1

| accepted