Community Profile

# John D'Errico

### Retired

3,392 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 details...

Contributions in
View by

Matrix inversion using "pinv" or any other technique
The answer to this question is to take a recent course on numerical linear algebra. Literally so. OR, do a lot of reading, becau...

20 hours ago | 0

Solved

The average of the second largest values
Given a matrix, find the average of the second largest values in each row. The same value does not exist on a row. Example: ...

1 day ago

Solved

Fibonacci-Sum of Squares
Given the Fibonacci sequence defined by the following recursive relation, * F_n = F_(n-1) + F_(n-2) * where F_0 = 0 and F_1 ...

1 day ago

Solved

Volume of a Simplex
Return the volume of a <http://en.wikipedia.org/wiki/Simplex regular _n_-simplex> with a unit side length. Results are up to...

1 day ago

Solved

Volume difference between Ellipsoid and Sphere
Given an ellipsoid of semi principal axis (a,b,c) find the volume of the difference between this ellipsoid and the sphere with...

1 day ago

Solved

Perimeter
Given a sequence of points forming a closed path (first and last points are coincident) return the perimeter value. For example...

1 day ago

Solved

Return the Fibonacci Sequence
Write a code which returns the Fibonacci Sequence such that the largest value in the sequence is less than the input integer N. ...

1 day ago

Linear Regression with Y as your Dependent Variable
xe=[0 .02 .05 .1 .2 .3 .4 .5 .6 .7 .8 .9 .94 .96 .98 1]; ye=[0 .192 .377 .527 .656 .713 .746 .771 .794 .822 .858 .912 .942 ...

1 day ago | 0

I'm not sure what your question is. You have a valid license for R2015b. However, you said two things that seem a bit inconsiste...

1 day ago | 0

Convert an ODE to algebraic equations
It has been a while since I used these methods, so I will not go that deeply into the answer. But there are multiple ways to sol...

1 day ago | 1

| accepted

Solved

Find nearest prime number less than input number
Find nearest prime number less than input number. For example: if the input number is 125, then the nearest prime number whi...

2 days ago

Solved

sum of non-primes
The sum of the non-primes no larger than 10 is 1+4+6+8+9+10=38 Find the sum of all the positive non-prime integers that do no...

2 days ago

Solved

Extra safe primes
Did you know that the number 5 is the first safe prime? A safe prime is a prime number that can be expressed as 2p+1, where p is...

2 days ago

Solved

Pernicious Anniversary Problem
Since Cody is 5 years old, it's pernicious. A <http://rosettacode.org/wiki/Pernicious_numbers Pernicious number> is an integer w...

2 days ago

how can split image to 4 parts using "reshape" or using another way?
Why not try something? That is how you will learn. A = rand(10,10) A = 0.93614 0.13657 0.90563 ...

2 days ago | 0

Deactivation switch for implicit expansion
I believe it is not possible to disable the expansion. Personally, I like having it, just that people don't like change. There i...

4 days ago | 2

Um, I think you need to look CAREFULLY at the data you have. Then think carefully about what you need. An inflection point is...

4 days ago | 0

Unable to define ScatteredInterpolant function v
v IS the 4th column, thus temperature. The other variables are your independent variables. So essentially, scattered inter...

4 days ago | 0

| accepted

Generating two classes of points
Why would rand or randn NOT be of use here? For example, what do you know about a bivariate random sample? How far out can yo...

4 days ago | 0

| accepted

How to interpolate data points in 3 directions with non unique grid coordinates
Scattered data interpolation is the case where your data points are randomly scattered, not on some regular lattice. Interp3 ...

4 days ago | 0

| accepted

Hello everyone! I need your valuable help here.
April = 4; Sept = 9; S = size(mat); seasons = reshape(mat,[12 14 12 30]); seasons = seasons(:,:,April:Sept,:); ...

4 days ago | 4

| accepted

Spherical Interpolation of data
So, you have some function, known at points only on the surface of a sphere, where the locations are given by Latitude and Longi...

5 days ago | 0

HELP REQUIRED IN PROGRAMMING
Sorry. But this is just a bad idea. A novice style or programming, only headed for worse things to come. What will you do wit...

6 days ago | 3

Improving my code - I'm trying to generate a checkerboard of size (222,786); length of each size 20. My code did work but I feel the logic can be improved. Kindly help.
Shiver. Yes, it can be improved. :) Honestly, what you have done is highly convoluted. That is not bad for someone learning to p...

6 days ago | 1

| accepted

What is a simple code for the chapman cycle involving only hydrogen and oxygen.This is my code but it should produce a curve but it only produces straight lines?
You have massive problems with the dynamic range of your numbers here, to the extent that you literally cannot solve this in dou...

6 days ago | 0

Efficient way of storing a triangular matrix
If all of your matrices are the same size, it is trivial to store them, extracting the upper triangle. Just create one vector...

6 days ago | 1

Finding zero values of a matrix for different parameters
You want to know what combinations of K and Ma give you zero? help contourc Yes, I know that a contour plot does not se...

7 days ago | 0

| accepted

how can i fit smooth curve through these points ?

7 days ago | 2

| accepted

what size does a image need to be for
The optimal image size? Simple: 1 pixel. So a square image of size 1x1. Fast. Efficient as hell. Only requires ONE colo...

9 days ago | 0