# 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**

Verify analytical expression: derivative of an integral with undefined function

You define a function of a variable as I do here: syms n omega phi(t) T diff(int(phi*exp(-i*n*omega*t),[0,T]),T) Looks like y...

alrededor de 5 horas ago | 0

Three terms exponential fit without initial guess

There are a lot of misconceptions here. Can you do a fit without ANY initial guesses? No. Any nonlinear fit will use initial gu...

alrededor de 9 horas ago | 2

Bound 3D function with asymptote

Your problem is that zlim ONLY limits the plot axes. It does not impact the shape of the surface itself. Instead, define the sur...

alrededor de 14 horas ago | 0

| accepted

Fitting a sine to data

Are you doing something fundamentally wrong? Sort of, yes. Fitting periodic functions has a probem, in that you will need to pr...

alrededor de 14 horas ago | 0

How can I avoid pseudo random and confirm natural random ?

It is not possible to do that. For example, suppose I give you a number, but I won't tell you where it came from, or how I gener...

alrededor de 14 horas ago | 1

24 Hours for run my for loop

The crystal ball is soooo foggy today. I just cannot look into your computer to know why your code is slow. All the darned thing...

1 día ago | 1

Find equally (almost equal) distanced elements in an array

As a subtly different answer, now that I understand your question a little better, consider this idea. My goal in this answer wi...

1 día ago | 0

Find equally (almost equal) distanced elements in an array

You don't really say enough about your question to make it easy to solve. How long will these vectors be? How many non-zeros? Do...

1 día ago | 0

How to calculate the mean of all neighbouring elements in a matrix

This is actually trivially easy to solve, using a nice trick that is well worth remembering. (Note that this is a great trick th...

1 día ago | 1

Retreive standard deviation from noise

If it is purely white noise stored in the vector, then just use std. Even if the noise is not gaussian, std will still apply. S...

1 día ago | 0

Exponential curve fitting with nonlinearleastsquares methood

You DID get an exponential fit. However, your data is relatively noisy. And it does not span a wide enough interval so that the ...

3 días ago | 0

How to call a function over a rolling window of data?

Yes, there are more sophisticated ways to do this. But for gods sake, why not just write a loop? You don't say what size the re...

4 días ago | 1

| accepted

Different commands to do spline interpolation, are they the same?

Can two different functions exist that happen to do the same thing? Of course. MATLAB is a complicated language, that was create...

5 días ago | 1

Increasing number of data points by linear interpolation method

The problem is, as voiced by others, is it depends on why you are doing this. Certainly you can use interpolation tools to perfo...

5 días ago | 1

Converting a list of binary numbers to a decimal numbers

You have a list of binary numbers, as a character array. So zeros, ones, and a decimal point. (Personally, I think that should b...

5 días ago | 0

Why is lscov giving me a very different solution to a simple system with an analytical solution?

This is not the fault of lscov. As you have written it, t_matrix is quite well conditioned. There is only one solution to the pr...

6 días ago | 0

Curve fitting tool does not respect the upper and lower limits of parameters of custom equation

Sorry, but the confidence limits are not impacted by the bounds. To get better confidence limits they would need to do considera...

6 días ago | 0

A compact way to find single digit numbers (i.e. numbers between 0 and 9) and replace them with two digit numbers

In MATLAB, you CANNOT store a number in a numeric format as one that has a leading zero. If you want to convert the numbers to ...

8 días ago | 0

| accepted

How to calculate the rotation of this egg?

Find a bounding box, where the box can be rotated, not a box that is aligned with the axes. Find the orientation (angle of incl...

8 días ago | 0

| accepted

How can I find negative factorial ? (-0.5)!

Simple. Yes, you could use MATLAB, IF you knew that the extension of the function factorial(n) onto the real line is just gamma(...

8 días ago | 1

Out of memory error

You have 20000 variables. So fmincon will be computing a Hessian matrix internally of size 20000*20000 = 4e8. But that matrix is...

9 días ago | 2

Why does smoothdata give bad results at the beginning and end of a dataset?

Think about it. This is really classic behavior, completely expected. Imagine the smoothing routine as a mathematical implementa...

9 días ago | 3

| accepted

Value of infinite integral is different

First, What is the correct value of this integral? syms k K = (k.^3).*(1+(2.35.*(k).^(2/3))) Just looking at it, I see a func...

10 días ago | 1

How can I get the symbolic steady state vector of a Markov Chain?

Easy, peasy. For example, given a simple Markov process, described by the 3x3 transition matrix T. T = [.5 .2 .3;.1 .4 .5;.1 .1...

10 días ago | 1

How to extrapolate given data to find more number of points?

Your words ask how to do interpolation. However, then you ask about extrapolation. The two problems are VERY different. To quo...

11 días ago | 0

Array indices must be positive integers or logical values?

MATLAB does not allow an index of 0. The FIRST element of an array or vector is indexed as x(1). In your loop, what was the ran...

11 días ago | 0

MAXIMUM MATRIKS IN MATLAB

Since you did not say which one to leave non-zero, I'll asssume that all values equal to the maximum are retained. A = randi(20...

11 días ago | 0

| accepted

Backslash does not provided the solution with the smallest 2-norm

It seems the gist of your question comes down to the idea that for a wide matrix, MATLAB should (in your eyes only) always produ...

13 días ago | 0

Solving Trigonometric Equations with More Than One Variables

You need to understand that first, the use of solve like this will probably fail. You have 4 equations, but only 3 unknowns. Sol...

13 días ago | 0

| accepted

I need an expression between two symbols R and a connected within a large order determinant.

Sorry, but not going to happen. Ever. Why not? There are multiple reasons why this will fail, so you are tilting at impossibly h...

15 días ago | 0