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John D'Errico


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Retired

4.887 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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Answered
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. ...

etwa 3 Stunden ago | 1

Answered
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 ...

etwa 5 Stunden ago | 0

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Answered
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...

etwa 14 Stunden ago | 1

Answered
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...

etwa 22 Stunden ago | 1

| accepted

Answered
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^...

ein Tag ago | 0

Answered
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...

ein Tag ago | 0

Answered
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...

ein Tag ago | 0

Answered
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...

2 Tage ago | 0

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

3 Tage ago | 0

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Answered
'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 ...

3 Tage ago | 0

Answered
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...

3 Tage ago | 0

Answered
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...

4 Tage ago | 0

Answered
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...

5 Tage ago | 0

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Answered
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

7 Tage ago | 0

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Answered
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...

7 Tage ago | 0

Answered
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...

7 Tage ago | 0

Answered
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...

7 Tage ago | 1

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Answered
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...

7 Tage ago | 0

Answered
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 ...

9 Tage ago | 0

Answered
How to fit custom polynomial equation?
You could download polyfitn from the file exchange. But if you already know how to use the curve fitting toolbox, then just spe...

9 Tage ago | 0

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Answered
How to efficiently plot functions?
Wyhy not try it? I don't have t or y, so I'll make them up. t = (1:10)'; y = rand(10,12); plot(t,y) Actually, I don't need...

9 Tage ago | 1

| accepted

Answered
How can I creat a lower triangular with one vektor avoiding for loops?
Will it always be a matrix of that form? Or will you next ask how to fill the lower triangle with a fully general set of numbers...

9 Tage ago | 1

| accepted

Answered
How to use for loop and if else condition for multiple conditions
First, you don'r need a for loop that runs over system, sine you re just assigning it one value! That is, this: for system = 1 ...

10 Tage ago | 0

| accepted

Answered
Distance between a point and the intersection of two spheres
This is confusing, possibly because of how you are trying to solve it. I think you are working too hard. The intersection betwe...

10 Tage ago | 0

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Answered
How to plot polynomial function correctly?
Hmm. Why does this feel like deja vu? (Answer: I just answered almost the same question for someone else, not 5 minutes ago.) d...

10 Tage ago | 1

Answered
Plotting a graph with a confusing equation
How to lie with statistics. ;-) (Yes, that is the name of a little book I read long ago.) My point is, not that you or anyone i...

10 Tage ago | 1

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Answered
Matrices with different numbers of equations
You know the size of the matrix. You already know you need to use zeros to initialize it. A = zeros(2*N,2*N); b = zeros(2*N,1)...

10 Tage ago | 1

Answered
plotting a natural cubic spline
Are you allowed to use existing code? So if you have the curve fitting toolbox, you can just use csape. x = 0:4; y = [1 3 3 4 ...

10 Tage ago | 1

Answered
Find the vector sum combination that gives the minimum vector length
First, NEVER store data in multiple variables like this. Instead, LEARN TO USE ARRAYS. There is no reason why you cannot store a...

11 Tage ago | 2

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Answered
Unrecognized function or variable 'carsmall'
This is not a question of you updating your version. I can see what you did, but not what you were hoping to do. Suppose I try t...

11 Tage ago | 1

| accepted

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