# John D'Errico

### Retired

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

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**Content Feed**

Using nested FOR() loops to populate a matrix

You have a solution. It works. Do you need for loops, or worse, nested for loops? Of course not. The entire point of this answer...

etwa 19 Stunden ago | 1

Why is it that when I am trying to create a function, the run button at the top turns grey?

You DON'T use run on a function. That makes no sense I'm afraid. Instead, functions in MATLAB are things you would call from ei...

2 Tage ago | 0

Matlab code for solving nonlinear equations

Actiiually, this is almost trivial. Seriously. It is. All of the trig terms are just known constants. And everything else is in ...

2 Tage ago | 1

| accepted

if and sum not working together

I'll say the same thing, but differently. As @Steven Lord points out, you cannot represent the fraction 1/3 exactly as a decim...

4 Tage ago | 1

Looping if between 2 numbers

As @Jeffrey Clark said, the & operator is a LOGICAL operator. Perhaps what you want to do is have a loop over a discontigous dom...

6 Tage ago | 0

How can I solve a system of non-linear equations with complex numbers?

WHY NOT TRY IT? Assuming you really intended for the second equation to use sind(120)... syms theta r eq1 = 0 == 2*cosd(240) +...

6 Tage ago | 0

| accepted

what formula do I have to put for calculating by using MATLAB?

Start here: help sum Then spend some time on the MATLAB Onramp tutorial, since this is a basic question.

7 Tage ago | 0

| accepted

Question about how the isosurface function works

isosurface cannot use interpolation? Why not? All that is necessary is the ability to perform LINEAR interpolation, between pair...

7 Tage ago | 0

| accepted

Extreme points of a polyhedral set

Was it really necessary to put a picture of the equations into your question, when simple text was just as easy? That means, in ...

8 Tage ago | 0

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How to approximate a multivariable arctan function?

@Sam Chak has suggested an interesting idea in a comment. However, while it is not a bad idea at first glance, I suspect it will...

8 Tage ago | 1

Formatting of result values.

You cannot write it in that form, at least not easily. Yes, you could write a formatting code. But you would need to write it, s...

8 Tage ago | 0

vectorized code is more time consuming than a simple for loop

It is not uncommon to have vectorized code be slower than a brute force loop. Why? The word "vectorization" can refer to many d...

9 Tage ago | 2

Problem with non-linear implicit equation using fsolve

a = 1.5; R = 190; bmax = 0.0024139; bmin = 9.779e-10; Since you do not tell us the values of A and B, only the range, I'll...

12 Tage ago | 0

How to sort points clockwise or counterclockwise?

Can you compute the polar coordinates angle, around that mean? (Hint: use atan2. Don't forget to subtract off the mean FIRST.) ...

12 Tage ago | 1

Scaling variables for integration with ode15s

There is a reasonable chance your results may problematic, if you do not scale things. While you may get a result, you will have...

12 Tage ago | 0

1, 4, 7, 2, 5, 8, 3, 6, 9 serie

Yes, @Tom has given a great answer. The way I would solve it on any normal day. But, just perhaps, is there another way? There a...

12 Tage ago | 0

Sentiment Analysis Expand Contractions

Is it possible? Of course. Search for the possible contractions. Replace them with uncontracted forms. Note that SOME forms woul...

13 Tage ago | 1

Converting system of equations to form Ax=b

help equationsToMatrix For example. syms x y E1 = x + y == 1 E2 = x - y == 2 [A,B] = equationsToMatrix(E1,E2,[x,y])

13 Tage ago | 2

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How to assign a symbolic matrix to another new matrix?

You are NOT assigning a symbolic matrix to another "new" matrix, but you are instead trying to stuff symbolic elements into an e...

14 Tage ago | 0

Access contributor message threads on MATLAB Central

No. And, yes. Sort of. Is that a good answer? If the person you wanted to contact does not have messaging allowed, then you can...

14 Tage ago | 0

I need to change this code into one that can solve complex roots

Interesting. It does not work? :) Gosh, You could have fooled me. I'll try an example. (I've attached the code you gave, so it w...

14 Tage ago | 0

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Creating sub arrays from a larger array

DON'T split them into separate, named arrays. This is just a bad way to write code. It will create buggy, slow code, even if you...

15 Tage ago | 0

How to plot this implicit function? (It's one parameter also changes)

The vertical axis indicates the value of phi. F3 = @(x,y,phi) y.^4 + y.^2.*(2*x.*tan(phi)-1) + x.^2.*sec(phi).^2; fimplicit3...

15 Tage ago | 0

How to find limit of a function

What you have written is NOT a sequence, but a function of one variable. If you are asking how to find the limit of that functio...

16 Tage ago | 0

How to obtain an input-output relation for NN trainNetwork or similar functions

This is a common question, where someone wants to see a simple function they can write down and understand, from a complex tool....

16 Tage ago | 1

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How can i take the log2 of x plus 1 of a matrix

What function in MATLAB gives the log, with base 2? help log2 So what line of code would add 1 to x, and then take the log, ba...

16 Tage ago | 0

Why ''int'' and ''integral'' return different answers

As others have said, the problem with integral is because of the singularities. Numerical methods don't like singularities. zzz...

17 Tage ago | 0

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How to implement a description for variables in the code?

So you want a tooltip to appear, hovering over each variable or line of code, but have no explicitly written comments in the cod...

18 Tage ago | 0

| accepted

Interpolation for 2 dependent output data

Trivial. You just have TWO interpolation problems. Interpolate output1 as a function of the input. Then interpolate output2, als...

18 Tage ago | 0