John D'Errico

Retired

Last seen: Today | Active since 2006

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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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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...

22 hours ago | 0

Answered
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 ...

1 day ago | 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...

2 days ago | 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...

4 days ago | 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,...

5 days ago | 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] =...

6 days ago | 1

Answered
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...

6 days ago | 1

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Answered
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...

7 days ago | 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...

7 days ago | 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...

9 days ago | 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...

10 days ago | 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...

12 days ago | 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...

14 days ago | 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'...

16 days ago | 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 ...

17 days ago | 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...

18 days ago | 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...

19 days ago | 0

Answered
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...

22 days ago | 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];...

22 days ago | 2

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Answered
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...

26 days ago | 1

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Answered
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...

26 days ago | 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...

26 days ago | 0

Answered
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...

28 days ago | 1

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Answered
Plotting a volume in 3D
Your question is somewhat incomplete, as to what you mean by plotting a solid volume. I'll assume you may mean something like th...

29 days ago | 0

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How to numerically calculate volume under the curve?
You have a surface. (Not a curve as I might say.) How do you compute the area under that surface? Simple. Just call trapz twice....

29 days ago | 1

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Answered
ode45 integration issues for some choices of physical parameters,
This is an absolutely classic case for a stiff system, where for some sets of system parmeters, you have two or more things happ...

1 month ago | 0

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How to choose 60 unique coordinates ('A') from 600 coordinates('B'), nearest to 60 other coordinates('C')
As I pointed out to @Voss and @Star Strider, if the points in B mst be unique, then there is an issue. If you simply choose the ...

1 month ago | 1

Answered
finding variable of a given equation
gamma is a really bad choice of variable names, since gamma is itself a very useful function in MATLAB. Try to avoid doing these...

1 month ago | 1

Answered
solving nonlinear equation using newton method
You just misunderstand how to use the exponential function. In MATLAB, e^x is written as exp(x). That makes your fn as: fn = @...

1 month ago | 0

Answered
How to Set a Minimum Step Size for Variables in GA Solver (Global Optimization Toolbox)?
Really easy. Don't think of a step size for the GA solver. It does not take steps anyway, not like fmincon or other solvers of ...

1 month ago | 1

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John D'Errico

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