John D'Errico
Last seen: Today
Retired
5,312 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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Answer 10 questions that were unanswered for more than 30 days
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Contribute at least one answer each month for 36 consecutive months
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Awarded to John D'Errico on 10 Sep 2020
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fixed point Iterative method for finding root of an equation
To understand fixed point iteration, we need to know why and when it will diverge. When does it converge? For some problems, the...
6 hours ago | 1
| accepted
How to find all solutions to a system of two nonlinear equations?
Here is the rub - you are in trouble IF you really want to find ALL solutions of a system of totally general nonlinear equations...
1 day ago | 1
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inverse matrix calculation problem
You need to understand that the matrix a=[1 2 3;4 5 6;7 8 9] is singular. Therefore it has no inverse. You may as well have s...
2 days ago | 0
Matlab code for fractions
Confusing question. Do you know the value of s? s = 7 s = 7 >> 1.5/s ans = 0.214285714285714 >> format rat...
3 days ago | 1
Direction between points from [0,360]
The function atan2d gives angles that are from -180 to 180. Not a problem. This works: mod(atan2d(y,x),360) But you want the a...
5 days ago | 2
| accepted
PLEASE HELP ME CONVERT THIS EQUATION TO MATLAB CODE
Well, you did make an effort, and it was pretty close. But did you read my response? Did you read the help for tand and cosd? W...
6 days ago | 0
| accepted
Exponential Piecewise function creation.
A spline is not a piecewise exponential function, so using spline directly would be a waste of time, IF you truly need a piecewi...
6 days ago | 1
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minimum value of one inequality
This is just mathematics. r = 0.001; s = 7; n ALWAYS appears as 2^(-n/2). So calling that number x, first write the problem ...
6 days ago | 4
| accepted
Generate random sequence number with condition
I think you still do not appreciate that you cannot just say something is "random" and not define the distribution. For exampl...
7 days ago | 1
error using cross (A and B must have at least one dimension of length 3.)
I'm not sure what you want in terms of a 25000 dimensional cross produt between two vectors. What do you think it means? After a...
7 days ago | 1
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Diagonalising a Skew-Symmetric Matrix
Matrices that are defective will not have a complete set of eigenvectors. https://en.wikipedia.org/wiki/Defective_matrix " In...
8 days ago | 0
Molecules on flat surface by using the package of Atomistic Topology Operations
Without more carefully reading the help for the code you are using, when I go to that link, it describes Box_dim as a variable. ...
8 days ago | 0
Taylor polynomial of a not infinitely differentiable function.
Your question has absolutely nothing to do with MATLAB, but you seem to have made some effort. So I will point out that you may ...
9 days ago | 1
| accepted
Numerical integration over (0, x1)
If t is unknown, then you need to use symbolic tools to do the integration. syms x t K = 1/((exp(0.014342/(x * t)) - 1)) * (1/...
9 days ago | 1
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How can i compute an interpolated curve?
You don't provide the actual data. But you are asking to do something which is trivially easy for the eye to do, more difficult ...
9 days ago | 1
| accepted
how can I draw half circle in matlab ?
Sigh. You DID make an effort. It is not even a terrible solution, though what you did will not work, since it will at best be a ...
10 days ago | 2
| accepted
linprog cannot find solution
While you claim a solution exists, initially, I sincerely wonder if it truly does. I may learn differently by the time I am done...
10 days ago | 1
How to Run PSO with Real Data
You can't. That is, the optimal is just the optimal value at each point in your sample. You cannot do better than that, at least...
11 days ago | 0
How to solve for x in an sin equation?
No. There are INFINITELY many solutions. So you cannot say you want the OTHER solution. You can simply enough find a positive so...
12 days ago | 0
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linearly independent eigen vectors
And for some strange reason, you think that eig as applied to a diagonal matrix does not produce a set of independent eigenvecto...
12 days ago | 0
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How can large sparse matrix (Y bus matrix of order 800*800) be done inverse in Matlab?
An 800 by 800 matrix is barely what I would call large anymore. Perhaps 40 years ago, yes. Today, it is almost tiny. Ok, not tin...
12 days ago | 0
| accepted
How to subtract from a vector array and, if the answer is lees than 0, have it return a value of 0
Simple. No need to test anything either. Just use the max function. x = [1 2 3]; x(1) = max(x(1) - 2,0); x x = 0 ...
15 days ago | 0
Calculate factorial with 2 variables
Why do you feel you need to use loops? You should never write your own code for something that is far better computed using an e...
15 days ago | 2
Random number from 1 to 100 if the number between 20 to 30 add 100 if the number 50 to 60 minus 100.
I'll generate 10 samples. N = 10; X = randi(100,1,N); ind = (X >= 20) & (X <= 30); X(ind) = X(ind) + 100; ind = (X >= 5...
17 days ago | 0
Curve Fitting and Distribution Fitting
You have what, 13 data points? A model with many exponents in it? A model that is surely based on no real physical meaning of th...
19 days ago | 0
Integral of bessel function returns all zeros
It is a really bad idea to use gamma as a variable name because you are now stepping on the name of a very useful function in MA...
19 days ago | 0
| accepted
Sampling data using contraints
Use my randFixedLinearCombination tool, as found on the file exchange. (I did just post an update today, fixing a bug the code t...
19 days ago | 1
| accepted
Submitted
randFixedLinearCombination
Uniform random samples over a n-dimensional hyper-rectangle, subject to a linear equality constraint
19 days ago | 7 downloads |
recursive function to check a Palindrome
Why not try? I won't write it for you, as the entire problem is to make you think. I'll give you one hint, and I will hope nobod...
19 days ago | 1
Constructing a Maze with vectors
Insert NaNs between eack block of lines. X = [x,nan,x1,nan,x2]; Y = [y,nan,y1,nan,y2]; Now the various sets of line segments ...
20 days ago | 1
| accepted
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