Community Profile # John D'Errico

### Retired

Last seen: Today Actif depuis 2006

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 make change in the algorithm to start and end at a same point?
Your problem is, you want to force the code to return a tour that starts at point 1, and ends there. And that is where you are W...

1 jour il y a | 0

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Converting from syms to double
We don't see what is in that variable. But... If you cannot convert it to a double, then it is not a number. It has some symbol...

1 jour il y a | 0

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different time executions........
And you are surprised, because? Did you xpect exactly the same amount of time taken, EVERY TIME, to within a millisecond? Yes,...

1 jour il y a | 0

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ExB drift velocity code equation
I might guess that what you really want is to divide by the square of the norm of B. NOT by the elements of B squared. E = 0.1;...

2 jours il y a | 0

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why did the "text" function stop working while creating a new section in my live data
Whenever a function "stops working" you need to see if you have created a variable named text, or another function or script by ...

4 jours il y a | 0

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How to solve this equation?
As I see it, from your question, I think people have been missing the point. As has been said, there are no real solutions for s...

5 jours il y a | 2

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How to solve out of memory error when constructing sparse matrix
Remember that i and j and v also take memory. (222263280*4*2 + 222263280*8)/1024^3 So those three variables alone require 3.3 ...

5 jours il y a | 0

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What is 5A?
The obvious seems clear, since I recall arithmetic. FiveA = [15 10 25 5]; I think you DESPERATELY NEED to do the basic Onramp ...

6 jours il y a | 0

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Find the volume of the solid generated by revolving about the x-axis the region bounded by the curve y= 4/x^2+4,the axis, and the lines x=0 x=2
The question is now a year old, so I'll show how to solve it. @Mukesh chose to work with a different domain than the question as...

8 jours il y a | 0

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Matlab simulation for projectile motion
I think I don't understand their not understanding. (Ok, that seems confusing even to me, and I wrote it.) I would just write i...

9 jours il y a | 0

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Remove algebraic loop without delay
I don't know for sure how Simulink resolves the issue internally, but the answer seems straightforward. Consider the equation ...

11 jours il y a | 0

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Mathematical functions across variables
Is there a good reason why you would not just try this? A(1,1) + B(2,1) I think you are coming from a spreadsheet world. And f...

11 jours il y a | 0

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Draw samples using a Non-Gaussian distribution
I think you don't understand random numbers, AND you don't understand indexing in MATLAB. What does this do? random('poisson',1...

11 jours il y a | 0

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how does fmincon deal with ill-conditioned problem?
fmincon assumes you know what you are doing. (Is that not a good idea?) It tries to solve what you gave it to solve. Surely that...

13 jours il y a | 0

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Sub-optimal curve fitting, cannot find asymptotic value
I think you do not understand. Estimating an asymptote from data is a problem of extrapolation. It will be strongly dependent on...

15 jours il y a | 0

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unbounded in linear programming
First, read the warning message! "Warning: Length of lower bounds is < length(x); filling in missing lower bounds with -Inf." ...

15 jours il y a | 0

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Problem 2022. Find a Pythagorean triple
A simple enough solution... isTherePythagoreanTriple(1,2,3,4) isTherePythagoreanTriple(3,4,5,6) isTherePythagoreanTriple(12,1...

16 jours il y a | 0

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I don't know why you're saying it's an invalid expression. Help me
You NEED to learn about the dotted operators, thus .*, ./, and .^ operators. When x is a vector, for example, this: x = 1:5 ...

17 jours il y a | 0

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How can I simplify the symbolic expressions?
clear clc syms q_bar delta_o theta1 theta2 q S CL_alpha CL_delta b e KT eqn1 = (2*theta1 - theta2 - q_bar.*theta1 + q_bar.*th...

18 jours il y a | 0

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series computing is faster than parallel computing using parfor
There is no assurance that a parallel code will be faster than any specific serial code. ABSOLUTELY NONE. In fact, I can easily ...

19 jours il y a | 0

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Easy enough. g = [3/2 -1/4 -1/3]; gsym = poly2sym(g); gsym^2 And as you know, it squares the polynomial, but does not expand...

20 jours il y a | 0

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Optimization of a matrix with integers with nonlinear objective functions and nonlinear constraints
You are correct, in that fmincon does not provide integer constraints as an option, and that a tool like intlinprog does not all...

20 jours il y a | 0

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Newton Raphson Method: while loop
There are many, MANY ways to stop a while loop. For example... tol = 1e-8; err = inf; iter = 0; itmax = 100; while (abs(err...

20 jours il y a | 0

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Best way to count outputs for a 2D polynomial function along the curve of an implicit equation
Um, good luck at doing it at all well. Even anything in the right ball park would be a success. But you won't know how well you ...

21 jours il y a | 0

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Different Nonlinear Equality and Inequality Constraint Tolerances
As @Torsten said, the answer is a simple one. No. But sometimes, no can be a fuzzy word. :-) For example, suppose I have two co...

21 jours il y a | 1

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Converging on local minima using ga(). Ways to increase odds of finding global minima.
So big problems take time. Should this be a surprise? More time invested can be a gain, since here it will improve the ability o...

21 jours il y a | 1

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Name of islocalmin algorithm
You can read about it here: islocalmin But is there a specific "algorithm" that can be named? It seems a pretty simple algorit...

22 jours il y a | 0

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Detrending still leaves a slope
It depends on how you define detrend. Clearly, you have a different definition from me, at least, as well as the author of the f...

22 jours il y a | 1

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Operator '*' is not supported for operands of type 'function_handle'.
Too many errors in this code to list them all out. Starting at the beginning... eta_0 = 1 % Initial value of eta That line doe...

22 jours il y a | 1

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Why does it take MATLAB so long to print hello world?
To me, this all seems to be making a mountain out of a mole hill. Yes, if you are going to launch MATLAB, even with no gui inte...

23 jours il y a | 0