Community Profile

photo

John D'Errico


Last seen: Today

Retired

5.627 total contributions since 2006

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.

Contact

John D'Errico's Badges

  • Revival Level 4
  • Master
  • 36 Month Streak
  • Quiz Master
  • Promoter
  • Speed Demon
  • Top Downloads 2020
  • Top Downloads 2019
  • Personal Best Downloads Level 5
  • Editor's Pick
  • First Review
  • 5-Star Galaxy Level 5
  • First Submission
  • Thankful Level 4
  • Knowledgeable Level 4

View all

Contributions in
View by

Answered
How to reduce computation time of (sparse) matrix multiplication in Matlab?
The answer is easy. It depends! What does it depend on? How sparse are your matrices? A lot of people think if half the entries...

alrededor de 17 horas ago | 1

| accepted

Answered
How to plot only the real solutions of an implicit function ?
First, look at what you have. R = 0.35; L = 0.25; H = 0.4; syms x y F = sqrt(L^2-(R*(cosd(x)-sind(x).*sind(y))-H).^2) The ...

1 día ago | 1

Answered
Two equations of two unknown angles
First, I would recognize that you PROBABLY intended 200 to be a number in DEGREES, not radians. (200 radians would seem to make ...

1 día ago | 0

| accepted

Answered
Producing a NaN only where there is a NaN, zero otherwise
I'm always amazed at how many ways there are to accomplish anything in MATLAB. Here was my effort. It took me some time to think...

3 días ago | 1

Question


Producing a NaN only where there is a NaN, zero otherwise
This interesting question came up for me today. I was looking for a simple expression that can be used in a function handle, one...

3 días ago | 4 answers | 2

4

answers

Answered
how to solve this question in Matlab
This is now, what, the third or 4th time you asked this question? The first few times, it was explicitly about your homework ass...

4 días ago | 0

| accepted

Answered
Reverse geometric progression algorithm
Since you want a symmetric set of points around 0, first generate a set on the positive side of the origin, then just flip them ...

5 días ago | 0

| accepted

Answered
Matlab: Divide and Average Method
Its that new math. The supreme court redefined sqrt(4) as 1.68 just recently. So your code is correct. Now all we need to do is ...

7 días ago | 0

Answered
How to tell if a function was called from within Matlab or from system?
Perhaps you might try what are essentially different calls, where you pass information about WHERE your call is coming from. So ...

7 días ago | 0

Answered
How can I slove the maxtric
You want to slove a matrix? Sorry. Valentines day was 3 days ago. Too late for s"love". A is a column vector, composed of the e...

8 días ago | 0

Answered
Find an orthogonal vector
Never call a variable O. Consider how difficult it will be to find the bug one day, when you see or write a zero, instead of O. ...

9 días ago | 0

| accepted

Answered
Matlab does not show the curve equation in basic fitting
You misunderstand splines. A spline does not have a simple equation you can write down. And while in theory, you could write dow...

9 días ago | 0

Answered
How do I determine the linear part of a force-displacement curve?
You have already accepted Star's answer, so you may not even see this answer. But in fact, there is no linear part of such a cur...

10 días ago | 0

Answered
Fitting data to a polar equation
@Omar Ashour It seems from this last comment that you re making some progress. There are some points I should make. First, wh...

11 días ago | 0

| accepted

Answered
why isn't determinant function working?
I think your problem may be due to the imaginary part of this rather nasty function. F = matlabFunction(DET1); F(1) ans = ...

11 días ago | 0

Answered
Fitting the data to power law using least square method
Let me look more carefully at your data, as there are some thigns that REALLY bother me about the approach you wish to use, as w...

13 días ago | 0

Answered
Correspondence between optimization outputs and symbolic variables
The problem lies in your code. First, you have an obvious error in the code you show. I'll guess you just used too many or too f...

13 días ago | 0

Answered
Which equation does Matlab use to fit a Normal distribution?
I think you misunderstand, as there are several things happening here. A normal distribution fit, that is, finding the paramete...

13 días ago | 1

Answered
How to search functions for mat use
You can use my mgrep function, downloadable form the file exchange. In your case, if you want to search for use of that file in...

13 días ago | 1

| accepted

Answered
Sparse of symbolic matrix
Sorry, but NO. Sparse storage does not applly to symbolic matrices. Even if it did, this would virtually not help you to speed ...

14 días ago | 1

| accepted

Answered
Please explain how this matlab code works works and what it does
It can be almost impossible to figure out what undocumented code does, especially if we are not even told what it might be desig...

14 días ago | 1

Answered
Confidence interval of regression line
If the line has KNOWN coefficients, then a confidence interval is meaningless. If you want to compute confidence intervals arou...

14 días ago | 0

| accepted

Answered
matrix retrieving given certain determinant
You want to generate a random matrix with a known determinant? n = 7; % The size of the matrix Dtarget = 12; % My target deter...

16 días ago | 0

Answered
Matrices with unknown elements multiplication
Define the eements of the matrices in terms of symbolic unknowns. Then use solve to determine the unknown elements. Note that un...

16 días ago | 0

| accepted

Answered
How do i rotate a matrix over set of points.
No. You do not want to rotate a matrix. You have a list of points that lie in the plane, described as cooordinates in each colum...

16 días ago | 0

Answered
Is there a way to define a new built-in function?
As others have said, you need to start using your MATLAB search path. Once you put a file in your own personal search path, it w...

16 días ago | 1

Answered
Overdetermined Linear System with Binary-Solution
You CANNOT use lsqr on integer (binary) problems. Period. I don't know why you think you could do that. You cannot use intlinpr...

17 días ago | 0

Answered
Help solving directional cosines
A=[-130.342, -75, -55; -75, -130.342, 65; -55, 65, -130.342]; svd(A) That small number as the third element of the s...

18 días ago | 1

| accepted

Answered
How to calculate error of trapz() function?
This is not a question about MATLAB, but a question about understanding numerical integration, and perhaps a bit of statistics. ...

18 días ago | 1

Answered
Output result's format?
These are symbolic expressions you are showing. The format command has NOTHING to do with symbolic expressions. It applies only ...

20 días ago | 1

| accepted

Load more