John D'Errico
Retired
4.283 total contributions since 2006Mainly retired from Eastman Kodak. (Of course, Kodak itself is now semi-retired. I don't think I had any influence in that.) I still write MATLAB code as I find something interesting, and I do attempt to write new tools to put on the File Exchange when I think I can make a contribution.
However, I DON'T answer direct e-mail questions, and I do NOT do homework. In general, your homework is YOUR problem, not mine. Please do NOT e-mail me with your homework problems or student projects. If I was willing to answer your questions, I would very rapidly become overwhelmed, because one question is never just one simple question.
When I'm not doing something with MATLAB, you might find me playing bridge, either in the club or online on BBO.
Professional Interests: MATLAB, numerical analysis, mathematical modeling
Avocational interests: Bridge, woodworking, woodturning
John D'Errico's Badges
Answer 10 questions that were unanswered for more than 30 days
Awarded to John D'Errico on 22 Jan 2018
Contribute at least one answer each month for 36 consecutive months
Awarded to John D'Errico on 20 Jul 2017
Accept 50 answers given by other contributors
Awarded to John D'Errico on 20 Jul 2017
100 of your answers have been accepted
Awarded to John D'Errico on 20 Jul 2017
Provide your first answer ever to someone else's question
Awarded to John D'Errico on 20 Jul 2017
Like a problem or solution
Awarded to John D'Errico on 13 Oct 2016
Be the first to solve a problem
Awarded to John D'Errico on 28 Aug 2016
Solve all the problems in CUP Challenge
Awarded to John D'Errico on 21 Aug 2016
Create a problem
Awarded to John D'Errico on 22 Jul 2016
Comment on a problem or solution
Awarded to John D'Errico on 28 Jan 2012
Solve a problem for the first time
Awarded to John D'Errico on 28 Jan 2012
Simulating a Markov chain
There seems to be many followup questions, it may be worth discussing the problem in some depth, how you might attack it in MATL...
etwa 2 Stunden ago | 1
random deployment of nodes
I don't see the problem. You don't start by solving the entire problem in one line of code. You start by going as slowly as you ...
etwa 9 Stunden ago | 0
if condition for infinity
You cannot test for the word 'finite', and expect it to return a valid result, when compared to an inf value. x = inf x = ...
ein Tag ago | 0
Sum of a 4D matrix
The problem is a relatively easy one, as long as the total sum does not exceed 1. It gets nasty above that. I'll look at the pr...
3 Tage ago | 1
Linear Programming With geq constraints
You switch the sign of a constraint simply by multiplying everything by -1. I thought that was like elementary school math. Did ...
4 Tage ago | 0
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How to create a spline for data without sorting?
I can certainly do it with interparc. But it gets tricky, because interparc is set up to find points that are designated in term...
5 Tage ago | 1
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How can I reverse C = mpower(A,B)
Um, you can't. Information tossed into the bit bucket is irretrievably lost. In your example, A1 is upper triangular, with 0 on...
5 Tage ago | 0
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Extract rectangular grid from triangulation
The simple answer is to just round the points to a lattice. That is, just assign each point to the nearest lattice point. Since ...
5 Tage ago | 0
non linear equation with single root
fzero does not find a root, cannot find it, because it has no zero crossing. That is a requirement for fzero. Effectively, there...
6 Tage ago | 1
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Curve Fitting Equation result
Those are approximate confidence limits on the variable as estimated. (Not always very good limits, as I said, approximate.) I...
6 Tage ago | 0
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coefficients of the polynomial - the least squares method
Sort of correct. But I see at least two subtle problems. First, you have 9 data points. So a polynomial with as many coefficien...
7 Tage ago | 0
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excel linear regression trouble vs excel linear regression
Simple enough. polyfit(x,y,1) ans = -0.002965 1.7919 Or: regress(y',[x',ones(length(x),1)]) ans = -0.002965...
8 Tage ago | 0
Solving linear equations with large matrices
Enough information now that I'll hazard an answer. By the way, the logic behind suggesting GMRES is NOT that your matrix is spa...
8 Tage ago | 1
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Why is the answer from the calculator and matlab different?
Because 455^100 is a computation done in DOUBLE PRECISION. Assuch, it goes well beyond the limits of what a double can represent...
9 Tage ago | 1
How to solve an equation, with infinite solutions, to find only n number of solutions?
Provably getting the FIRST 5 solutions is essentially impossible on a completely general function, as it is trivial to write a f...
10 Tage ago | 0
Solving system of n equations
syms a x b y EQ = y == a*x + b; isolate(EQ,x) ans = x == -(b - y)/a
10 Tage ago | 0
How do I create a repeating number series?
LEARN TO USE MATLAB. 0.25:.5:25 ans = Columns 1 through 11 0.25 0.75 1.25 1.75 2...
10 Tage ago | 0
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interpolation of scatter data
First, your original contour plot. Next, the interpolated one. So much noisier. Interpolation does not necessarily make th...
11 Tage ago | 0
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How to Solve Non-Linear Equation with changing coefficient
Note there is no need to use fzero. Roots is entirely adequate, and more accurate. Roots also recognizes there are TWO real solu...
11 Tage ago | 2
Interp1 command, wrong number of input arguments
Read the help for interp1. With 4 input arguments: Vq = interp1(X,V,Xq,METHOD) specifies the interpolation method. The a...
11 Tage ago | 0
how to make 2d lookup table when having 3 vectors
The problem is, your data is insufficient to create a 2-d surface from only that data. (Yes, you CAN use a scatteredInterpolant,...
12 Tage ago | 0
Numerical solution of a matlab function.
This is just a continuation of the last time the same question was asked, and answered. https://www.mathworks.com/matlabcentral...
12 Tage ago | 1
How do I test a vector element by element for imaginary elements
What does the function imag return? Given that, what would imag( r ) ~= 0 tell you? see that it returns a true or false valu...
12 Tage ago | 0
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Print all possible matrix combinations for a given matrix
You are going mad because ... Your problem is poorly formulated. i.e., how close to S/3 do you need to be? For long vectors, y...
13 Tage ago | 2
Finding pythagoras triples when only c is known
Alternatively... Talk to Euclid. An old guy, maybe even dead by now. He gave us a formula for Pythagorean triples. https://en....
13 Tage ago | 5
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How can I make magic matrix if I know the diagonal
Not all problems have a solution. But sometimes, they do, IF you are willing to relax some conditions. A classical magic square ...
13 Tage ago | 4
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does the query points in gridfit function need to start from zero?
No. There is no requirement about needing to start from zero. In fact, those were WARNINGS, not errors. It MAY indicate a proble...
14 Tage ago | 0
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Data point missing in if statement
Let me explain separately, since you are misssing the point. The important point is NOT that there are duplicated points at (5...
14 Tage ago | 0
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Locating a point along a curve some distance away from an initial point.
Easy, peasy. That is, assuming you are asking about a distance in terms of arclength along the curve. If not, then the answer is...
15 Tage ago | 1
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how to get the numerical solution of Non linear equation for unknown variable
Confusing. That usually means the person is also confused. We are shown an integral on the left hand side. It is an integral ov...
17 Tage ago | 0