photo

John D'Errico


Retired

Last seen: Today Active since 2006

Followers: 2   Following: 0

Message

A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

Statistics

All
  • Most Accepted 2023
  • Editor's pick for Answers
  • Quiz Master
  • Promoter
  • Top Downloads 2023
  • Top Downloads 2022
  • Top Downloads 2021
  • Top Downloads 2020
  • Revival Level 4
  • Top Downloads 2019
  • Personal Best Downloads Level 5
  • Editor's Pick

View badges

Feeds

Answered
how write a matrix with specific features
I think you are confused about what you can do with MATLAB. Those constraints simply tell you the associated matrix for the grap...

ungefär 4 timmar ago | 1

Answered
I have a nonlinear equation with a symbolic variable and cant solve it.
Look carefully at your problem. n = 2.1; alpha0 = 0; syms p alpha eqn = p^(n+1) - alpha0*p^n + p -(alpha0 + alpha) == 0 So ...

ungefär 21 timmar ago | 0

| accepted

Answered
findging eigenvectors with eigenvalues
Most of the time when I see someone worry their eigenvectors are not correct, it is just because of a sign error on the eigenvec...

en dag ago | 1

Answered
Library function log10 not found when using fit
x = rand(10,1);y = x + rand(10,1); fit(x,y,'log10') It is almost always, ALWAYS the case that when this happens, you were prev...

3 dagar ago | 1

| accepted

Answered
iterative estimation of eigenvalues and eigenvectors by the inverse power method. Your MATLAB/Octave code shouldn’t be hardcoded. ● Calculate the eigenvectors and eigenvalues
Let me guess, you have a problem with this matrix. Does the matrix have any special properties? What, for example, are the eige...

4 dagar ago | 0

Answered
using PCA to filter outliers in MATLAB
I've attached my quick shot at an n-dimensional outlier tool, based on Mahalanobis distance. I am pretty sure it has some seriou...

5 dagar ago | 1

| accepted

Answered
How do I plot a symbolic equation that I have created?
By the way, there is NOTHING symbolic in the code you wrote. syms t % this makes t symbolic % no need to put decimal points ...

6 dagar ago | 0

Answered
scatter command not working
(It is good you are using the tutorials.) But first, learn to read the error message, an important skill in using MATLAB, unless...

8 dagar ago | 1

| accepted

Answered
Nonlinear optimization with branching solution space
Just solve 11 distinct problems, each of them continuous. Use a loop, setting x to each of the 11 possible values. Save each sol...

11 dagar ago | 1

| accepted

Answered
how to create nxn matrix with main diagonal that enters odd rows/columns with zero and even ones start with 2(n+1) sequence
Simple is to use diag. n = 5; % Now many non-zero elements will we have? N = 1:(2*n); % a simple index vector D = N.*mod(N-1,...

11 dagar ago | 0

Answered
Does I properly translate the equations in matlab code?
Ouch. That would be a miserable set of equations to try to code. (You have my sympathies.) I did some very quick spot checks, an...

11 dagar ago | 0

Answered
problem in curve fitting
C1 continuous? Is there a difference? Absolutely YES. C1 continuity, using circular "arcs" in 3-d? UGH. I'm a career mathemati...

12 dagar ago | 0

Answered
species go to negative values
Remember that the software does not truly understand your model, and what you are attempting to simulate in that model. It only ...

12 dagar ago | 0

Answered
Better "probabilities"?
How effective is rand? I'm not sure what you mean by "effective", or for that matter, "advanced". It is a state of the art rando...

13 dagar ago | 1

Answered
Need help solving heat equation using adi method
You say it works for sufficiently small values dt. With that exp(t) term in there, do you seriously expect it to work well for...

14 dagar ago | 0

Answered
Non-linear Algebraic 36 equations unsloved
Actually, a starting value set like ones(36,1) is often a dangerous thing to do. Making all of the starting values the same can ...

15 dagar ago | 0

Answered
math model of neural network fitting
As is often the case with such "models", there is nothing you could write down, at least not easily, and without nasty arrays of...

15 dagar ago | 0

| accepted

Answered
About Fluid dynamics in a porous medium...
As @Torsten said, this is far too vague a question. I would suggest starting with a far simpler problem, especiially good is if...

16 dagar ago | 0

| accepted

Answered
inversing huge Y Matrix
As always, I'll start by saying that computing the inverse of a matrix is a bad idea. And of course, you don't say what you thin...

16 dagar ago | 0

Answered
How can I solve this implicit function in MatLab?
Trivial, in some eyes. ;-) This is one of the simpler implicit problems you might write down, since a direct solution exists in ...

16 dagar ago | 1

| accepted

Answered
How to add unknow parameter in matrix and solve it by use det() syntax for finding w
syms w; m1 = 1.8; m2 = 6.3; m3 = 5.4; m4 = 22.5; m5 = 54; c2 = 10000; c3 = 500; c4 = 1500; c5 = 1100; k2 = 1*10^8; k3...

17 dagar ago | 0

Answered
solving linear systems of equations
A long forgotten question and one with an answer that may not be appreciated by @Chloe St John, given that multiple questions by...

18 dagar ago | 0

Answered
MathWorks Administrator Account Privileges
Contact customer support at MathWorks. That is not Answers. We cannot help you directly. https://www.mathworks.com/support/cont...

18 dagar ago | 0

Answered
When integrating acceleration do you need to convert velocity?
When you keep on subtracting off the mean, you do strange things to the result. But you need to consider what a constant of inte...

19 dagar ago | 0

Answered
How to efficiently solve a system with an infinity number of solutions?
Note that a solution need not always exist for all n. When n==1, and so A is a 1x1 matrix, it is completely known. So unless yo...

19 dagar ago | 0

Answered
How can I calculate the integral of Legendre function P(n,theta) ?
@Shreen El-Sapa I think you do not understand that a Legendre polynomial is meaningless over some other interval. It has no spe...

20 dagar ago | 1

Answered
Create a matrix and a map of Hydrologic Soil Group values using integer or character values
MATLAB does indeed allow you to produce a character matrix, with those characters. However, I assume you have scattered data, wi...

21 dagar ago | 0

Answered
Determine row vector out of matrix with most evenly spaced and distributed values
Simple. Sort of. But you need to define what equal spacing means to you, and how you will measure the deviation from equal spaci...

21 dagar ago | 0

| accepted

Answered
Are polyshape vertices preserved reliably without floating point errors?
Um, probably, yes. But potentially no. Yes, because on most operations, you will just be indexing into the original set of vert...

22 dagar ago | 1

Answered
Integrate function by for loop
As always look carefully at your code. Learn to use the debugger. It would tell you the problem, and in which line there was a p...

22 dagar ago | 0

Load more