John D'Errico

Retired

Last seen: Today | Attivo dal 2006

Followers: 21 Following: 0

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A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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How to use "predict" to get x value for a given y value?
Huh? Of course polyfit works. It does NOT require the x values be distinct. I'm not at all sure why you think that is necessary....

circa 17 ore fa | 0

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What information is stored by p1/p2/... in this code sample?
Undocumented, uncommented code, from an unknown source? Shiver. No. It is not a distance computation. That much I can say. The...

1 giorno fa | 1

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Attempt to execute SCRIPT plot as a function,how to solve it?
Don't name your script plot. In general, don't use existing names of supplied functions for your own functions or scripts. You ...

2 giorni fa | 0

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How to identify such functions as addpath that are coming with MATLAB?
Follow two rules when you are writing or providing functions to run in MATLAB. Rule # 1: NEVER put your own functions in the Ma...

3 giorni fa | 0

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Are there MATLAB functions or scripts to perform boolean operations on triangulated solids?
Are there such codes in MATLAB? Yes. I wrote them. intersect, union. In 2-d and in 3-d. (Not sure if I wrote a setdiff variant. ...

7 giorni fa | 0

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Product of matrices over finite fields
Even in the simple case of F_2 matrices, I'm not sure it is easy to do better than brute force. But no, you don't need to write ...

9 giorni fa | 1

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Multi-Parameter function minimization with many many parameters
Let me try to help, a little at least. Why is fminsearch so bad at high dimensions? It is just not designed for that class of ...

11 giorni fa | 0

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Solve nlp equation system with variables spanning more than 40 powers of 10
Are the variables potentially going to vary by that many powers of 10? If so, then you would have the solver work in a log space...

14 giorni fa | 0

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Solve 𝑔 ′ ( 𝑥 ) = 0 for z in terms of N, a positive integer
First, it is not a cubic equation! Yes, you can replace sqrt(x) with a new variable z, thus a transformation. But doing so can ...

15 giorni fa | 0

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With k（0<k<0.5） and u（-1<u<1) as independent variables and x and y as dependent variables, how do you graph x and y, respectively, for a system of implicit function equations?
You have 2 parameters, k and u. If you were to fix those parameters, then you could solve for the solutions. There would be zero...

15 giorni fa | 0

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4 nonlinear equations by using Newton's method
Why are you writing Newton's method code to solve a problem? Never write code to do numerical methods work, if far better code i...

17 giorni fa | 0

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Is there a function in matlab to find temperature, density ecc.. values outside the standard atmposphere?
Um, not really, and certainly not easily or in any good way. Something like temperature can vary HUGELY outside the atmosphere,...

18 giorni fa | 0

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Issue regarding the result from symbolic computation
If you have this: a11 = 1/2; a12 = 1/2; a22 = 1/2; A = [a11 a12 0; a12 a22 0; 0 0 0] The eigenvectors were found as: [V,D] =...

19 giorni fa | 1

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Calculating Perpendicular Distance Between Detected Edge and Smoothing Function
If your curve is represented as a sequence of points (which is always possible) then you can use my distance2curve utility. It f...

19 giorni fa | 1

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How to draw the function relationship graph between two or three variables, where these variables are solved by a system of equations.
Not everything you might want to do has an answer. You ask to "draw" the relationship between variables. (For a fairly vaguely s...

20 giorni fa | 0

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How to create a smooth curve through data points?
Just coming back to this, as I did not see the data provided. (Sorry to @Gerard Feeney) But this is a difficult thing for multi...

21 giorni fa | 1

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Is it possible to select the parameters in the approximation equation using MATLAB?
Yes. Use the curve fitting toolbox. help fittype help fit Note that the estimates of these coefficients will be very uncertai...

22 giorni fa | 0

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HI, while doing a small calculation part, from my class note, in matlab, im getting the result as inf, can i know how to convert the inf value into realnumbers.
Of course D0 is undefined. You created the variable Do. There is a difference between the number 0 and the letter o. That Do is...

23 giorni fa | 0

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Need help with curve fitting
Um. NO. Yes, there is a language problem, and what you write is confusing. But you are not doing what you claim to want to do. W...

25 giorni fa | 1

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solving a nonlinear equation with complex numbers
syms R positive % positive implicitly implies real also syms X real syms Zo Z=(R*1i*X/(R+1i*X)); r=(Z-Zo)/(Z+Zo) r = simpli...

27 giorni fa | 0

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Warning: Equation is badly conditioned. Remove repeated data points or try centering and scaling.
Do NOT use polynomials to model data like this In fact, do not use high order polynomials, pretty much ever. FR = load('FR.txt'...

29 giorni fa | 2

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Recursively reversing large vector efficiently
An old question with an already good answer. Regardless, it explicitly asks about recursive schemes to flip a vector. And I can ...

30 giorni fa | 0

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Fixing biased random number generation
What is the goal of this? That is a good question, as asked by @埃博拉酱. You should recognize that the result of this operation w...

circa un mese fa | 0

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My end value "tc2" comes out as "NaN + NaNi", in the following script and I cant figure out why.
A NaN means you are doing some operation that has no meaningful result. For example, what is 0/0? 0/0 A mathematician will tel...

circa un mese fa | 0

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Sparse matrix memory understanding
I think you missed a zero. By the way, 5% sparse is NOT at all what I would consider sparse, or for there to often be a gain. L...

circa un mese fa | 0

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Fittype and fit do not work as expected (in a curve fitting)
x = [1 4 9 15 25 35 45 55 65 75 85 95 150 250 350 450 900]; y = [0 335 28 37 9 4 3.5 2 1 0.7 0.6 0.5 0.3 0.1 0.01 0.005 0.001];...

circa un mese fa | 2

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Newton Rapson method code question
Actually, this is surprisingly nice looking code. (A true compliment from me, given most of the student codes we see on here!) Y...

circa un mese fa | 1

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Converting an STL file to a 3D Surface/Equation
Um, I think you misunderstand a few things. It seems the STL model actually has thickness. So you have exported the entire thi...

circa un mese fa | 0

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I want the genetic algorithm to begin with intial parameter and this is not happened can you help me for making the genetic algorithm begin with the intial parameter?
I think you don't understand GA. It does not use a start point. It starts with an initial population of points from the sample s...

circa un mese fa | 0

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How do I convert a symbolic expression to a string?
Simple enough. Note the changes I made to your last line only. I could also have done it using character vectors, but then I wou...

circa un mese fa | 1

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John D'Errico

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