Community Profile # John D'Errico

### Retired

4.660 total contributions since 2006

Mainly retired from Eastman Kodak. (Of course, Kodak itself is now semi-retired. I don't think I had any influence in that.) I still write MATLAB code as I find something interesting, and I do attempt to write new tools to put on the File Exchange when I think I can make a contribution.

However, I DON'T answer direct e-mail questions, and I do NOT do homework. In general, your homework is YOUR problem, not mine. Please do NOT e-mail me with your homework problems or student projects. If I was willing to answer your questions, I would very rapidly become overwhelmed, because one question is never just one simple question.

When I'm not doing something with MATLAB, you might find me playing bridge, either in the club or online on BBO.

Professional Interests: MATLAB, numerical analysis, mathematical modeling

Avocational interests: Bridge, woodworking, woodturning

View all

Contributions in
View by

how to plot an ellipse having her equation?
First, learn how to write a function. fun = @(x,y) x.^2 / 25 + y.^2 / 9 - 1; Note the use of the .^ operators. They will be im...

alrededor de 4 horas ago | 0

Unable to predict data well enough
I would point out that your code shows you using the first SEVEN data points, not the first 10, despite your claim otherwise. n...

alrededor de 8 horas ago | 0

how can i find the intersection point between the vertical lines and the curve (xmin,ymin) ?
The red curve is a piecewise linear interpolation, not really a curve, just connect the dots by the plotting routine. The green...

alrededor de 10 horas ago | 1

| accepted

lsqcurvefit: is the output of this function unique for a given set of initial conditions (and deterministic model)?
The problem is, that is not your code. Not all of it. That is just how you call lsqcurvefit. We do not see the pandemic1Dall2 co...

alrededor de 14 horas ago | 1

change a logical array value based on the index of another matrix
If you want to create x on the fly, then just do this: x = A > 4; If you for some reason really want to modify an existing vec...

1 día ago | 0

| accepted

What's the meaning of instrucment sound in Matlab?
Let me just answer this as if you asked for an explanation of what a sound is in the world of MATLAB. For example, if we try: l...

2 días ago | 0

vector to upper and lower triangular matrix
What you fail to see is that while your code works for a 3x3 matrrix, it must always fail for any n other than n==3. You want t...

2 días ago | 0

| accepted

double differentiation and double integration of sine wave
This is not a question about MATLAB, just understanding some basic mathematics. At least, understanding calc 101. First, you ne...

3 días ago | 0

Diagonal/Symmetric matrix
I don't even think your code works for a 3x3 matrix. The matrix it produces is OD OD = 81 23 18....

3 días ago | 0

| accepted

How do I open a pcode (.p) file created in a version older than MATLAB R2007b? My Matlab version is R2018b.
You cannot edit a .p file, if that is what you mean by open. That is true in any version. If the .p file is too old, but you s...

4 días ago | 0

How to transfer a Matlab toolbox I have in my machine to the machine of a colleague ?
If this is a toolbox that you have purchased from Mathworks, you cannot give it to someone else. If this is a toolbox you have ...

4 días ago | 0

For loop for matrix division
Why would you want to use any loop at all? For example, if A is an mxn matrix, and V is a vector of size mx1, then consider what...

4 días ago | 0

Can someone explain the concept of B= null(A) in simple words?
Think of A as a vector pointing someplace in a 5 dimensional space. Got that? It points somewhere. Now, in 5 dimensions, we co...

5 días ago | 1

| accepted

How to get more decimal places in my output?
In fact, it does NOT neglect that term. It is in there, just too small for you to see in only 4 decimal places. help format Yo...

6 días ago | 1

How to remove last characters from String using mod?
It is generally a bad idea to use names for variables that are already useful function names. So here rem is one such bad idea. ...

7 días ago | 2

| accepted

Random sampling of elements from an array based on a target condition in MATLAB
Are you looking for an exact match to V1? An approximate sum equal to V1? If so, then how close of a tolerance do you need? Is ...

7 días ago | 1

how to use large numbers
Depending on what you are doing, you can use any of several tools. For example ... The symbolic toolbox: sym(17)^173 ans = 7...

8 días ago | 1

| accepted

is max built in functions
Yes. max is definitely a built-in function. As such, use of it will have been (sadly) outlawed by your assignment.

8 días ago | 0

| accepted

Calling a multivariable system of equations
I think you do not understand functions. And, well, I suppose this is a not uncommon problem for new users. There are at least t...

9 días ago | 0

I need to have eigenvalues of this matrix including symbols "m" and "n"
Actually, it is pretty easy, and the solution arrives almost immediately. A=[0 1/sqrt(3*n*m) 1/sqrt(3*n*m) 1/sqrt(3*n*m) 1/sqrt...

9 días ago | 0

How to find integral of this function.
No, that is not going to have any closed form solution. One suggestion in the comments was to try vpaintegral. If it does not ...

10 días ago | 0

| accepted

how to numerically define 1/x^2+0.4/(60-x)^2
If x is a vector or array, then you are trying to compute element-wise operations. But / and ^ and * are all operators that are ...

10 días ago | 0

Extrapolating rate constants from reaction data
l,k, m are just scalar symbolic variables. When you write solve(k) for example, it solves the problem k == 0 What is the ...

10 días ago | 0

how to use Discretize syntax
Funny. Actually, both of the other answers have missed an important point. While they properly describe how to use discretize, b...

11 días ago | 1

Using Polyfiti, Polyval, and plotting
Ok, now that I know where you are coming from, I'll pose this as an answer. It looks correct to me. The call to polyfit will cr...

12 días ago | 1

| accepted

all combinations of numbers
It is often true that people decide to do something unimaginably huge, because something small seemed easy enough. Computers are...

12 días ago | 0

Double for Loop to find root of polynomial
lambda=2; Quadratic_For_Omega_Squared=@(L,M)[1,-(L^2 +2 * M^2 +1 -lambda), +M^2 * (L^2 +M^2 -lambda)]; L=1:-0.1:0; M=1:-0.1:0...

12 días ago | 0

| accepted

I need to plot hyperbolas with ellipses
Well, first, you need to write down the equation for the hyperbola. Seems silly, or maybe obvious, but you can't do anything wit...

12 días ago | 0

taylor series expansion for acos(1-x)
Actually, the expansion you ask for does NOT exist. Why not? Because. I hope that is a good enough answer.. ;-) Seriously, the ...

12 días ago | 1

| accepted