# John D'Errico

### Retired

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.

**Content Feed**

how do i use two varaibles with values of somewhere from 1 to 9 to make a 2 digit number

What if you added them together? Maybe multiply one of them by 10 first? What would that do?

24 hours 前 | 0

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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...

3 days 前 | 0

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...

4 days 前 | 0

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,...

4 days 前 | 0

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;...

4 days 前 | 0

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 ...

6 days 前 | 0

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...

7 days 前 | 2

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 ...

7 days 前 | 0

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 ...

8 days 前 | 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...

10 days 前 | 0

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...

11 days 前 | 0

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 ...

13 days 前 | 0

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...

13 days 前 | 0

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...

13 days 前 | 0

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...

15 days 前 | 0

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...

17 days 前 | 0

unbounded in linear programming

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

17 days 前 | 0

Problem 2022. Find a Pythagorean triple

A simple enough solution... isTherePythagoreanTriple(1,2,3,4) isTherePythagoreanTriple(3,4,5,6) isTherePythagoreanTriple(12,1...

18 days 前 | 0

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 ...

19 days 前 | 0

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...

20 days 前 | 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 ...

21 days 前 | 0

Elevar un polinomio al cuadrado

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...

22 days 前 | 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...

22 days 前 | 0

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...

22 days 前 | 0

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 ...

23 days 前 | 0

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...

23 days 前 | 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...

23 days 前 | 1

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...

24 days 前 | 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...

24 days 前 | 1

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...

24 days 前 | 1

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