John D'Errico

Retired

Last seen: Today | 2006 年からアクティブ

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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...

1日前 | 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 ...

1日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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...

6日前 | 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...

7日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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日前 | 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...

22日前 | 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日前 | 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...

26日前 | 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...

26日前 | 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...

27日前 | 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...

28日前 | 1

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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日前 | 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日前 | 1

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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...

約1ヶ月前 | 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 ...

約1ヶ月前 | 1

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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...

約1ヶ月前 | 1

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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 = @...

約1ヶ月前 | 0

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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 ...

約1ヶ月前 | 1

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John D'Errico

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