John D'Errico

Retired

Last seen: Today | Con actividad desde 2006

Followers: 22 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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Cannot Understand a Command
I would guess what they did was to ask you to write a matrix by something like the following description: M(a,b) = a + b w...

alrededor de 19 horas hace | 0

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Solving non linear system with fsolve
Whenever you have a problem with hugely varying constants in it like this, it makes sense to consider if you should transform th...

2 días hace | 0

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How do I find the equation of points on a spline curve?
This is a question that gets aslked many many times about splines. And, well, you can't easily get a simple equation, as there i...

3 días hace | 0

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Too many input arguments error in objective cost function using fminsearchbnd
Did it even work using fmincon? I can't test that out, since we lack your data. And lacking your data, I can't test fminsearchbn...

4 días hace | 1

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How to map voltage to battery percent?
This is just a simple linear interpolation. Think about it! Suppose you subtract 45 from the voltage. When V was zero, you now ...

5 días hace | 0

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Constraint set to be a real number
First, constraints like: AV_constraint_1 = isreal(A_v); are not differentiable. Sorry. They can't be used in fmincon. Well, y...

6 días hace | 0

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Numerical integration (Trapezoid, Simpson, Gauss)
"shouldn't Gauss' 3 points method give the best value for the integral ?" Why? In fact, no. There is no reason for that to be t...

6 días hace | 0

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Why does MatLab give non integer values for whole numbers?
It is not even remotely ridiculous. Are you seriously claiming that the vector [0.7071;0.7071] is NOT a null vector? Any mult...

8 días hace | 1

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Does anyone know how to get solve to work with one of the variables being a range
Solve does not directly allow you to define a variable as being in a range, but assume will help you out, as I show below. Anywa...

9 días hace | 0

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Algorithm which finds lower bound of the epigraph of a discrete 2D curve which is not a function (i.e. fails vertical line test)
Is there an algorithm that solves it in some slick way? Not that I know of. How would I solve it? Treat this as a way to find ...

10 días hace | 1

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Simplify in GF(2)
In the help docs for simplify, we see: "S = simplify(expr) performs algebraic simplification of expr." The key word there is A...

12 días hace | 0

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Hello I am solving a lp problem and linprog shows the wrong answer. If I solve it with fmincon, I get the answer.
H= @(i,j) exp(-abs(i-j)); % anonymous function m= 4; noise_pow= 1e-9; g= [15; 12; 9; 6]; A= [-H(1,1), g(1)*H(2,1), g(1)*H(3,1...

12 días hace | 1

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Cumtrapz integration drift with time
This is expected behavior. And reducing the time step WILL reduce the problem. And it IS something purely mathematical, yes, you...

13 días hace | 0

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Numerical search for the singular points of a complex matrix
I'm sorry, but the use of det for anything like this is a bad idea. How did they do this in 1972? Sigh, they used determinants ...

16 días hace | 1

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Vectorized code slower than loops
Read the response by @Steven Lord again, in case you missed it. (Actually, that is always good advice for any of his responses.)...

16 días hace | 2

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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....

18 días hace | 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...

19 días hace | 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 ...

19 días hace | 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...

20 días hace | 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. ...

24 días hace | 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 ...

26 días hace | 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 ...

28 días hace | 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...

alrededor de 1 mes hace | 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 ...

alrededor de 1 mes hace | 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...

alrededor de 1 mes hace | 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...

alrededor de 1 mes hace | 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,...

alrededor de 1 mes hace | 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] =...

alrededor de 1 mes hace | 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...

alrededor de 1 mes hace | 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...

alrededor de 1 mes hace | 0

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