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# John D'Errico

### Retired

4.897 total contributions since 2006

(Please don't contact me. I won't answer questions.) A retired mathematician, numerical animalist, woodworker, bridge player.

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Finding odd and even values without functions
A = 1:10; A == fix(A/2)*2 ans = 1×10 logical array 0 1 0 1 0 1 0 1 0 1 As long as A is composed of...

etwa 7 Stunden ago | 0

the purpose of %f
They seem identical to me. See? The result is exactly the same. ;-) sprintf('%d',pi) ans = '3.141593e+00' sprintf(...

etwa 8 Stunden ago | 0

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How to measur the inclination angle of a palne?
Is there a way? NO. Sorry, but absolutely not since two points do not determine a plane. There are infinitely many planes that ...

etwa 8 Stunden ago | 0

Whats wrong with this 45 degree line on the plot?
Appearances can be deceiving. Why do you think the line is NOT at 45 degrees? (I know, silly question, but there is a point in i...

etwa 8 Stunden ago | 0

How can I find zero root for fifth eigenvalue of a matrix
Sadly, the "fifth" eigenvalue of a matrix has no meaning, since the eigenvalues are not assured to arrive in any special order. ...

etwa 9 Stunden ago | 0

Constrained polynomial regression with the constraint in coefficient
You are trying to estimate alpha, given a set of data points in the form of (x,y) pairs? Where alpha enters into BOTH coefficien...

etwa 11 Stunden ago | 1

Different ways to find limits?
So my response of a simple, succinct "Yes" is not enough? Drat. It did answer the question as asked. Actually, I was thinking a...

etwa 13 Stunden ago | 1

Defining Triangular mesh with delaunay and inpolygon ?
Easy peasy. And there is no need to bother with inpolygon here. [x,y] = meshgrid(0:.1:1); xy = [x(:),y(:)]; xy(xy(:,1) > xy(:...

etwa 20 Stunden ago | 1

How to convert string "26/7" into a double variable?
Whilst I am one of the people who tends to equate eval with evil... str = '22/7'; eval(str) ans = 3.14285714285714...

etwa 21 Stunden ago | 1

Matlab Solve a system of equations for a set of data
You get huge numbers, because you are trying to use symbolic tools here, but with double precision numbers. See what happens her...

ein Tag ago | 1

Composite Boole's rule
Looks like you made a serious effort. First, let me find Boole, not something even most mathematicians would remember off hand. ...

ein Tag ago | 1

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How to find intersection between line and curve
Just because the only tool you own is a hammer does not mean every problem must be treated as itf it is a nail. Similarly, just ...

ein Tag ago | 0

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Optimisation algorithm ga and fmincon
Athul has already explained it pretty well. Let me try to expand on that, to add some ideas or possibilities. Many nonlinear p...

2 Tage ago | 1

Getting weird results when calculating an integral using rectangle method
Look carefully at what you did. vec1 = pi/180*(0.005:0.01:14.995); Now, what is the stride between elements of that vector? Wh...

2 Tage ago | 1

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Finding a number with conditions while using for loop
Why use a loop? ;-) Lets see, the smallest INTEGER with the desired property is 14404. We can get that as: n = 120; >> m = n^...

3 Tage ago | 1

Portfolio Optimization in support of Monte Carlo method.
You cannot use a tool like fmincon to optimize a stochastic function. That is, any function where repeated calls to the function...

3 Tage ago | 0

inverting variables with two matrices
Too late to be of any value to the OP, but others may have the same question... In general, if you have LINEAR surfaces, thus p...

3 Tage ago | 0

Lower Triangle of Matrix
No. You cannot tell triu to fill with ones instead of zeros. That does not mean what you are asking is impossible, just that you...

3 Tage ago | 0

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How can I generate random natural numbers between min and max range?
help randi

4 Tage ago | 0

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'solve' function always returns zero for the case it should not be zero!!!
Surely you cannot claim that 0 is not also a solution. The solution you know of may be the solution you want, but that does not ...

4 Tage ago | 0

Cannot solve symbolic equation annalytically
"Does anybody has an idea why the function (which is basically only a difference of sums of polynomials with some logarythmic fu...

5 Tage ago | 0

gaussian elim with rref(M) over Gf(2)
Far too late for this question, but in case others want help... You seem to have asked two questions. First, how to create a sy...

5 Tage ago | 0

Volume of overlapping ellipsoids
The simple solution is just to fill a 3-d array with voxels that are inside each ellipsoid. So, if a voxel is already filled, th...

7 Tage ago | 0

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generate 0 and 1
rand() < 0.6 If you want a random binary sequence of length n, then this is sufficient: rand(1,n) < 0.6

8 Tage ago | 0

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interrupt a function when it takes too long
This is not what parfor is designed to solve, nor even what you could reasonably solve with parfor. Since you are calling the f...

8 Tage ago | 0

To create a code that differentiate any function
Well, you write a complete version of a set of symbolic tools, that can parse any function provided, and know the rules for diff...

8 Tage ago | 0

How can i extrapolate data?
Extrapolation is a dangerous thing to do. Best left to someone with sufficient expertise that they know when they are doing some...

9 Tage ago | 1

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How to Get Answers in Non-PolyGamma Form?
(I'm sorry that my answer is coming 9 years too late to be of any significant value to you personally. But someone else might fi...

9 Tage ago | 0

Making contours in polar plot
You could at least spell my name right, since you had it right in front of you. Regardless, it turns out that you changed your ...

10 Tage ago | 0