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# John D'Errico

### Retired

4,725 total contributions since 2006

Please don't contact me. I won't answer questions.

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rotating this curve 20degrees
I would normally ask why not try it yourself, but I realize there are some issues that can easily catch you here. H = plot(t,sd...

11 hours ago | 2

Why 4.8/1.6 is not equal to 3?
While there has been a lot of good discussion in the other answer, let me add a few points. When you type 4.8 in MATLAB, does ...

3 days ago | 1

How can I solve linear equation system in parallel?
You already are doing that! That is, decomposition uses all of the cores you have available for large problems. Watching my ac...

3 days ago | 1

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How can I get confidence intervals when the Jacobian matrix has an almost zero vector?
This is probably not a failure of the assumption of Gaussian arrors, though that may indeed be the case too. I cannot know. Wha...

3 days ago | 0

Can I run MAtLab on mac
Yes. Apparently so. https://www.mathworks.com/support/requirements/matlab-system-requirements.html

4 days ago | 0

Fit a conic section without mirror image hyperbola
This goes back to basic algebra. When does a conic section describe an ellipse versus a hyperbola? https://en.wikipedia.org/wik...

4 days ago | 0

Distance between points of a 3D centreline
Why not try diff? For example, what does diff(CL,[],1) do? TRY IT! What is distance? Does that give you something you might b...

5 days ago | 0

Signal into tolerance range - Comparison algorithm
It is often the case when my answer wants to be both no and yes. That is, no, there is no direct tool that does what you seem to...

5 days ago | 0

How to graphically represent the global minimum of an optimization problem with more than two variables?
Do you have a multi-dimensional holographic monitor? Yes, I know, this will not be invented for many years if ever, but that is ...

7 days ago | 0

Fast method to find average pairwise distance of a very large matrix?
You cannot compute the 100 billion pairwise distances, because the matrix won't fit in memeory. (Ok, symmetry reduces it to be o...

7 days ago | 0

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How to get multiple outputs from a function?
[x,y] = subfuntest(a,b); When you call it with no arguments, it returns only the first, putting it in the default variable name...

8 days ago | 1

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how to find the sum of rows in an array, that fit a condition?
When a problem is too complex to solve, then break it down into SMALLER parts, that you can handle. You want to know how many r...

8 days ago | 1

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Normal Distribution Specifying parameters
Hint: What does normcdf tell you? (In fact, I think this totally gives the answer away, IF you understand what the CDF means.) ...

9 days ago | 0

Solve equationsystem (A*V).'*B*(A*V)=C for matrix A
As it turns out though, your problem is actually quite simple. Assume that V is full rank. As long as that is true, then as can...

9 days ago | 0

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Does the cubic Hermite spline interpolation of a monotone data with known slopes guarantee the monotonicity in interpolation segments?
pchip always gaurantees a monotonic interpolant if the data is itself monotone. However... If you provide the derivatives yours...

9 days ago | 0

MATLAB equivalent to ls -l
It depends on what you want from it. What exactly are you looking for? D = dir MAY give you much of what you may want, if you ...

10 days ago | 0

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How to write matlab code for modular multiplicative inverse in cryptography
A multiplicative inverse modulo some number p means that mod(x*xinv,p) == 1 That is, x has a mutiplicative inverse modulo p,...

10 days ago | 2

Why Power of Matrix with decimal values gives really big numbers?
This is basic linear algebra. I think you do not understand what is happening, or perhaps you do not understand Markov transitio...

10 days ago | 2

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When using interp3, do the input grids need to have evenly spaced values?
No. They do not need to be EVENLY spaced. So a grid spacing of [1 2 4 8 15 17 23 100] is entirely valid. Though depending on the...

10 days ago | 0

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Matlab: what happends under the hood when choosing 2 seeds far away with rng
The "separation" of two seeds is completely irrelevant. Separate them by 1 or 1e6, and they are just different seeds. If you use...

10 days ago | 0

Efficiently Running MATLAB: system specifications?
My suggestions would be: As much memory as you can afford. This allows you to vectorize solutions sometimes, offering improved ...

11 days ago | 0

Hi, i have a function which is function of a unknown constant ''á''. For each a there is a corresponding curve..i want to search that function curve for a set of ''a'' values which should have maximum peak value...
This is just a 2-dimensional optimization. fminsearch will suffice. You have some known function, a function of r, as well as t...

13 days ago | 0

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taylor series expansion with initial condition
Why not try it! ??? Make an effort. For example, this seems the obvious thing to try. So what does this do? syms x f(x) p f1=...

13 days ago | 1

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What capability would you want to see added to the symbolic toolbox in the future?
My own wish list starts with the large integer capabilities... A direct modular multiplicative inverse. Note that you can get e...

13 days ago | 1

When I do the standard deviation for the 2 arrays by hand I get a different answer than Matlab. Ive had 2 colleagues check and we all got the same answer; is there a problem with my code?
How can we possibly know if there is a problem with your code? You fail to show how you computed the standard deviation. std2 is...

13 days ago | 0

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how to solve this non-linear equations?
It is pretty easy to find at least one solution. vpasolve will do so, and my guess is, fsolve will do the same. syms v w p=30;...

13 days ago | 0

Convert Nx1 matrix into a single number
There are probably a gajillion ways to do this trivially. Since A is a vector of numeric digits, stored as numbers, the simples...

14 days ago | 1

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solving third degree modular equations in matlab?
Far too late for an answer. Sorry, as I just saw this question. But it is also perhaps quite a bit easier than you may think. A ...

15 days ago | 1

Spiroglyphic digital image processing
To be honest, I don't see the problem. Start with a black and white image. Create a new image of the same size that is all bla...

15 days ago | 0

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