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John D'Errico


Last seen: Today

Retired

5 631 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.

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Answered
I want to create normally distributed random variables, and refer to them as my independent variables
The answer is, DON'T. https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamic...

3 dagar ago | 0

Answered
sum of elements of an array
B = cumsum(A); You could have learned about this function by reading the help for sum. At the bottom of the help, you would see...

5 dagar ago | 1

Answered
results in the form of integral
Just wanting a result from some computation to have an analytical solution is not enough. Sometimes it requires additional mathe...

5 dagar ago | 0

Answered
Symbolic Math is reordering my subtraction
syms x_k(t) y_k(t) L x_kD = diff(x_k,t) y_kD = diff(y_k,t) rRk = sqrt(x_k^2 + y_k^2) rTk = sqrt(x_k^2 + (y_k-L)^2) rRkD = ...

6 dagar ago | 0

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...

7 dagar 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 ...

8 dagar 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 ...

8 dagar 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...

9 dagar 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...

9 dagar 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...

11 dagar 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 ...

11 dagar 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 ...

14 dagar 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 ...

14 dagar 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...

14 dagar 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. ...

15 dagar 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...

16 dagar 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...

16 dagar 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...

17 dagar 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 = ...

18 dagar 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...

19 dagar 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...

19 dagar 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...

20 dagar 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...

20 dagar 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 ...

20 dagar 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...

21 dagar 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...

21 dagar 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...

22 dagar 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...

22 dagar 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...

22 dagar 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...

22 dagar ago | 1

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