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# John D'Errico

### Retired

4,800 total contributions since 2006

(Please don't contact me. I won't answer questions.) A retired mathematician, numerical animalist, woodworker, bridge player.

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complex function inverse plot
Note that the natural log function is NOT written as ln in MATLAB, but just as log. Next, in general, it may be impossible to ...

22 hours ago | 0

Matrix dimensions must agree
You understood that you needed to use a dotted operator here: x.^12 There are also ./ and .* operators. For a VERY good reason....

1 day ago | 0

Write a function [sn, n] = mySumPi(tol), which outputs 𝑆n and n for the smallest n such that |𝑆n − pi| < tol
Ok, you are at least now getting close. Your code is still convoluted. And you have the wrong terms you create. Look carefully...

5 days ago | 0

Creating a simpsons rule matrix
Simple. Just create a matrix that alternates 4, then 2, then 4, etc. Then append a new first and last element of 1 to the result...

5 days ago | 0

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converting a matrix sequentially in to single column
A = rand(600,12); B = reshape(A,[30,20,12]); B = permute(B,[1 3 2]); B = reshape(B,[30*12,20]); I created B there as the des...

5 days ago | 0

How to write a loop that does not increase by +1?
A for loop can have any increment. Even a vector of numbers can be the increment. And it need not be in any order. Some examples...

5 days ago | 0

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Is it possible to use runge-kutta 4th order method to solve a equation with three different variables? For instance I have a equation : dy/dt= (R-0.135y)/P
It looks like you do not have THREE different variables. You have P, which I presume is a constant? Do you know the value of P...

6 days ago | 3

Using nested for loops to plot multiple approximations of Eulers method
Smile. Think about what you did. I think I know what you wanted to achieve, but look more carefully at what you have here. for...

7 days ago | 0

Help Creating the following matrix
Very easy, really. A = zeros(3,4); A(1,1) = 3*eye; A(1,3) = 2*ones; A(1,4) = 2*ones; A(2,2) = 3*eye; A(2,3) = 2*ones; A(2...

8 days ago | 0

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Contact customer support. Answers is not that. So we cannot help you directly in any real way. https://www.mathworks.com/compan...

8 days ago | 0

Fitting a sigmoid curve using curve fitting tool box
The problem is, there are many functional forms that people think of and call with the generic name "sigmoid". We can find a few...

9 days ago | 0

Can anyone explain for loop ? And nested loops.
How can we do better than to suggest you read the help for for? It has examples in there. help for doc for A simple for loop:...

9 days ago | 0

How to write while a set Q is not empty do the following in matlab?
What function tells you if a vector is empty? (Hint: isempty) What do you want? Not empty. So what is the logical negation oper...

10 days ago | 0

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Solving of vectorial equations
You cannot do it, at least if these are completely general nonlinear equations, since there may be no unique solution for nonlin...

10 days ago | 1

Inverse of algebraic expression in Matlab
As is often the case, not all simple problems have an algebraic solution. In fact, as you have found, it is trivial to write one...

11 days ago | 1

The quotient and remainder of a number divided by another (Euclidean Division)
What is the problem? :) You did it correctly. Well, except for the very last line. n = 19 d = 3 r = rem(n,d) q = (n-r)/d di...

11 days ago | 0

need help on my matrix code
An if statement dose NOT work this way. You cannot use that single statement to act on each element of the array, independently....

11 days ago | 0

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so for when i try to mutiply the variable v my number is really big can someone explain why. The choose in is user input
I think it MAY be partly that you do not understand how to write numbers. Or, do you not understand how to write algebraic expre...

12 days ago | 1

Cylinder fit to a point cloud data
You seem to be way overthinking this. xyz = REAL_data; xyz0 = mean(xyz) xyz0 = -0.024621 -18.89 0.75025 xyzh...

13 days ago | 0

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I cant solve linear programming
Who can solve it? Most likely, nobody. Your problem is unbounded. I can go through some mathematics to reduce it to show more cl...

13 days ago | 1

Can anyone write a mathlab program for this question?
Can anyone write a mathlab program for this question? The answer is easy - Yes. I can. Do I win the prize? Oh. Wait. You asked...

13 days ago | 0

How can a matrix of randperm be generated with variable n*m?
SImpler than you think. M = 4; N = 3; [~,A] = sort(rand(M,N),1) A = 1 1 3 4 2 1 2 3 ...

14 days ago | 1

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Unrecognized function or variable 'x'.
Where exactly did you define the value of x? I see this line: %x^2=5-y^2 But there is the minor flaw of a comment. Anyway, th...

15 days ago | 0

Can someone help me solve this. I am trying to evaluate the integral.
You don't understand. Just because a sometimes useful mathematical way of writing the cube of a function like sin, is to write i...

16 days ago | 0

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negative x axis meaning
This is confusing as a question. You have a plot of some numbers. Some of them are negative. Of course MATLAB will extend the ax...

16 days ago | 0

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precision of calculation with Matlab
This must of course fail as you are doing it, since out must generally exceed 2^53-1, the limits of flintmax for a double precis...

16 days ago | 1

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Does someone has the Composite MicroMechanics COMM toolbox? Thanks!
Just contact the source. This link claims it to be freely available, by contacting the author. https://www.researchgate.net/pub...

16 days ago | 0

Question on pdepe solver
Why not just read the help? That is, first, I typed doc pdepe Quickly scan down through there, and I see that indeed, pdepe ...

17 days ago | 0

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