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# John D'Errico

### Retired

Last seen: Today Aktiv seit 2006

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

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minkowskiSum
Compute the Minkowski sum of any two polygons or polyshapes, convex or concave.

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Generalized Minkowski Sum calculation
https://en.wikipedia.org/wiki/Minkowski_addition The convex case is quite simple to solve. I could write code for that in a few...

etwa 14 Stunden vor | 2

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I need a graph to be smooth
You asked this question before. I answered it. In fact, you even show the code I wrote. And you accepted my answer then as I rec...

ein Tag vor | 0

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Why does Matlab's divisors function take so long when working on an ordinary integer?
You ALWAYS. ALWAYS. ALWAYS need to consider the arguments for a function. Does it work in double precision, or as a sym? Don't f...

ein Tag vor | 0

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boundry value third order problem
I don't know if this is homework. But it possibly is. So I'll just point you in a decent direction. And if you are going to sol...

ein Tag vor | 0

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Normalizing a set of data to zero
Do you want ALL of those minima to be zero? If so, then you will need to do something especially artful. If all you want is the ...

2 Tage vor | 0

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Random 3D Array of Cylinders with Random Rotation and Fixed Length
THERE IS NO SIMPLE SOLUTION. Accept that. For example, even for as simple a problem as random sphere packing, where you want to ...

2 Tage vor | 0

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Why my polynomial function is wavy
A simple rule applies: Polynomials oscillate. Not infinitely many times. But this is a fundamental nature of polynomials. As the...

2 Tage vor | 0

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NEED URGENT HELP! Code keeps returning the desired variables as empty 0x1
Must a solution exist for all problems? No. Of course not. Those empty syms are a signal that MATLAB was unable to solve your pr...

3 Tage vor | 0

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Trying to find area under my plot
You don't give your data. You show only a plot. So make a polyshape of it. Then compute the area. t = linspace(0,2*pi,50); x =...

3 Tage vor | 0

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Replacing special character 'É' to 'E'
Easy peasy. str = 'ABCDEFGHIJKÉÉÀÀÄÄabcdefghijkl' strrep(str,'É','E') If there are other special characters you want replaced...

3 Tage vor | 0

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Broad confidence bound range when fitting in Matlab
Wide confidence limits are typically a symptom, a reflection of uncertainty in some form. And unfortunately, we don't have your ...

4 Tage vor | 1

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How to perform svd without using the inbuilt function?
Why? That is, why is SVD not acceptable? Yes, you could write a complete code to compute the SVD, without using a call to SVD. ...

5 Tage vor | 0

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Why am I getting this error? "Array indices must be positive integers or logical values".
Is P0 a function? (NO. It is a scalar variable.) You have this: P_twitch_short(i) = P0(0.0258*(exp((stiff*RLS)))-0.0258); Did...

5 Tage vor | 1

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How to recover jpg or RAW images?
I'd be looking at my backups. (A GREAT thing to do.) Of course, if you are asking this question, there are no backups. Before th...

5 Tage vor | 0

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I need to smooth a 3d graph
x=1:10; y=1:21; z=[0 0 0 0 0 0 0 0 0 0; 0 0 0 0 0 -9 0 0 0 0; 0 0 0 0 -5 -7 0 0 0 0; 0 0 -10 -25 -15 -5 0 0 0 0; 0 -20 -32 -46...

5 Tage vor | 0

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How i can solve the problem of primitive root?
What you mistake is that a and p are represented as DOUBLES. Can you compute a number as you want to do? What happens? a = 3; ...

5 Tage vor | 1

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Best way to solve this non-linear equation?
dsolve is not used to solve a PDE. It applies ONLY to an ODE or a system of ODEs. help dsolve There are no symbolic solvers in...

6 Tage vor | 0

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Empty sym: 0-by-1
Don't write a whole mess of code, withput actually thinking about whether virtially the very first (significant) line you write ...

6 Tage vor | 0

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simpsons 1/3 rule calculating error
Before you worry about how to plot things, and compute the error, should you worry if your code is correct at all? Gosh, that ju...

6 Tage vor | 1

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How find the function (equation) of the fitting surface using interpolation (method biharmonic)?
This question is asked hundreds of times on the site. The answer is, there is no simple "equation" you can write down. That is t...

6 Tage vor | 1

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What distribution is appropriate for my data?
Why would you expect a distribution like that, with a strange hump on one side to have some predefined distribution that fits it...

6 Tage vor | 0

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Plot two functions in one diagramm with different y-axis limits
Easy peasy. x = linspace(-5,5,1000); y1 = sin(x); y2 = cos(x); y2(y2 > 0) = NaN; plot(x,y1,'b-',x,y2,'r-') ylim([-1,1]) y...

7 Tage vor | 1

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How to change Options of PSO during iterations?
Sorry, but no. You cannot change the options for a solver in the middle of the solve. This is essentially true for any solver. (...

7 Tage vor | 0

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Solving Nonlinear System of Equations with 10 variables
Use fsolve. You are trying to formulate this in terrm of a symbolic variables, but fsolve is a NUMERICAL solver. So you need to ...

7 Tage vor | 0

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i want to solve for 'L' using iteration method in MATLAB for the equation below
help fzero Consider that your question is the same as (gT^2)/(2*pi) tanh (2*pi*d/L) - L == 0

7 Tage vor | 0

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How to find the maximum element by length without a loop?
I'm a bit confused as to your question. If you want to choose the longer of two strings, then do as @Florian Bidaud suggests. Bu...

7 Tage vor | 1

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MatLab eig vs LAPACK
If I had to guess, you don't need to use it. A = randn(500); timeit(@() eig(A)) ans = 0.0800828164545 B = A + A'; timeit...

8 Tage vor | 0

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How to solve 'Equation solved at initial point' with fsolve?
As is often necessary on a problem like this, it helps to look carefully at what you have. x = sym('x',[1 2]); mu_earth = 39...

8 Tage vor | 0

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Optimization: Capacitated Facility Location Problem
First, what is the difference between the summation over i in a sum like this: sum(f(i)*yi)) and the dot product of two ve...

8 Tage vor | 1