# 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.

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**Content Feed**

Fastest possible prime number detection without using break or return

You did write working code to find primes. Well done there. But the fastest code? Without breaks, or returns. Easy peasy. Write...

14 hours ago | 0

I am new to matlab and I am trying to get prime numbers

But these loops will not result in prime numbers. (As you have found.) I think you are trying to do a simple sieve, or something...

15 hours ago | 1

How can i calculate the area under two curves that intersect?

1. Subtract the two curves. 2. Take the absolute value of the difference. 3. Compute the integral. Note that you ...

21 hours ago | 1

the arc using the chord

Your question is far too general, too vague to have an answer. There are infinitely many "arcs" that will pass through two poin...

21 hours ago | 0

MIL SIL equivalence check.

A literally impossible question to answer. Both far too broad, too vague, and yet extremely specific. It is not even clear what ...

1 day ago | 0

How do I create a variable H which contains the product of 5 and the values of B in the 1st and 9th rows, and the 1st and 2nd column.

Ok, first, you do understand how to extract the elements from B. Good there. I think maybe the question wording is confusing you...

1 day ago | 1

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Is this a logical Error in Matlab ? exp (pi*i*6) = 1.000000000000000 - 0.000000000000001i. WHY an i component ?, should just be 1

Remember that pi in MATLAB is not truly pi, any more than pi is 3.14, or even 3.14159. pi is a transcendental number. There are ...

2 days ago | 2

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How can MATLAB's extensive suite of functions for data analysis and visualization be utilized to import, process, and analyze simulation data, including performing frequency a

Um, learn MATLAB. That means you need to learn how to read the help, the documentation for those tools. Start by doing the bas...

2 days ago | 0

Symbolic integration has 3 solutions based on integration variable range, how to extract one of these?

Or do this: syms r umax Radius mom_2 = int((umax*(1-r/Radius)^(1/7))^2*2*pi*r,r,0,Radius) subs(mom_2,Radius,1) Note that it ...

4 days ago | 0

How do I find the most stable N consecutive numbers?

The mean difference? What is that exactly? In terms of mathematics? Are you looking for the 50 element consecutive subset with ...

4 days ago | 0

Possibly spurious solutions - Matlab blocked with no answers

You are attempting to solve for an analytical solution of 12 simultaneous nonlinear equations, in 12 unknowns. This, even if it ...

6 days ago | 1

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Solving goal programming problem with MATLAB

READ THE ERROR MESSAGE! What did it say? "Failure in initial user-supplied objective function evaluation. Optimization cannot c...

6 days ago | 0

How to set an axis with arbitrary, but equally spaced, scaling.

You could not plot versus the numbers 0,1,2,3, but then set the x-tick labels as you wish? x = [1/3 1/2 1 inf]; xfake = [0 1 2...

8 days ago | 1

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All possible combinations of a matrix

Did you intend to write 1.024^13? This is not even an integer, and only a little larger than 1. 1.024^13 So there are 1.3611 u...

8 days ago | 1

cubic spline interpolation - mixed boundary conditions possible?

You generally don't want to do this. That is, fit one spline, then construct a second spline to match the first. The result will...

9 days ago | 0

what's the relation between A , B and M,G for this Nonlinear system of equation ?

This is not even remotely a question about MATLAB. As such, it should arguably not even be on Answers. But I have a minute to re...

10 days ago | 0

Check code compatibility with older releases

A way to automatically check code compatibility with older releases, and see at what point a feature that you use makes your cod...

10 days ago | 0

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How to delay a signal using basic operators

This comes down to boundary conditions. So, first, a simple signal... x = [2 3 5 7 11]; Can't be any simpler than that. Now, s...

11 days ago | 0

Generate an orthonormal matrix H mHxNh rank(H)=r

Seems trivial enough. Not possible, at least not for this case. But trivially not possible. mH=5; nH=3; r=2; So a 5x3 array, o...

11 days ago | 0

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What does the error message "input must be real and full" mean?

The gamma function requires a real input. Although I recall that the symbolic version of gamma can handle complex input. But the...

11 days ago | 0

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Mod or Modulus operator in MATLAB

Be careful, as if you look for mod or modulus, you will often see the functions mod or rem, which essentially compute a remainde...

12 days ago | 0

Can a MATLAB home license be tied to a dongle?

You should contact customer support directly and ask your question. Answers is not that. Support may be able to offer an idea th...

12 days ago | 1

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How to fix "Number of equations greater than number of indeterminates. Trying heuristics to reduce to square system." error.

You need to understand what was wrong in your forumulation. You want to solve this system using symbolic tools. % define some c...

13 days ago | 0

Jumps in roots finding solutions

Lets spend some time to understand what happens. Consider the simple polynomial: y = x^5 + 3*x^4 + (2+t)*x^2 - t^2*x + (1+...

14 days ago | 0

Solving system of nonlinear equations using Matlab

fsolve does not apply constraints. It does not know that you think some coefficient should be some number. It does not care. All...

14 days ago | 0

Newton Raphson implementation, not converging, maybe error in implementation

There are some significant misunderstandings on your part that I want to clear up, as well as perhaps help you solve your proble...

14 days ago | 0

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Progress bar takes lots of time

Yes, a waitbar takes time to update. It looks like you are calling it a lot. And every time, it does an update. And since this i...

16 days ago | 0

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Adoption of Name=Value in Function Calls what is best practice?

What is best practice? I kind of like the new syntax. But best practice would seem to be whatever you like. At some point, might...

16 days ago | 0

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Solving non linear inequalities in 2 variables

The "range of variables? Those inequalities will generally describe some nonlinear "thing", even if they describe a bounded doma...

16 days ago | 2

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Question about transcendentals on symmatrix objects

A = symmatrix('A',[2,2]) That produces a matrix of the desired size, which is specifically symmetric, but see that it creates a...

17 days ago | 0