# 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.

**Statistics**

RANK**11**

of 264.950

REPUTATION**18.181**

CONTRIBUTIONS

**11** Questions

**6.336** Answers

ANSWER ACCEPTANCE **
45.45%
**

VOTES RECEIVED**3.938**

RANK**4** of 18.100

REPUTATION**62.204**

AVERAGE RATING**4.80**

CONTRIBUTIONS**57** Files

DOWNLOADS **1118**

ALL TIME DOWNLOADS**560304**

CONTRIBUTIONS**0 Posts**

CONTRIBUTIONS**0** Public Channels

AVERAGE RATING

CONTRIBUTIONS**1** Highlight

AVERAGE NO. OF LIKES**8**

**Content Feed**

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...

alrededor de 8 horas 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 ...

alrededor de 11 horas 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...

1 día 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...

4 días 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) +...

4 días 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.

5 días 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...

5 días 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 ...

6 días ago | 0

| accepted

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...

6 días 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...

6 días 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...

7 días 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...

10 días 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.) ...

10 días 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...

10 días 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...

10 días 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...

11 días 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])

11 días ago | 2

| accepted

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...

12 días 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...

12 días 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...

12 días ago | 0

| accepted

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...

13 días 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...

13 días 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...

14 días 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....

14 días ago | 1

| accepted

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...

14 días 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...

15 días ago | 0

| accepted

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...

16 días 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...

16 días ago | 0

In epsilon test for comparing equality of two numbers. How to improve the test?

Can you "improve" the test? What does improving it mean? How close do two numbers need to be considered the same? For example, ...

16 días ago | 0