Community Profile

# John D'Errico

### Retired

4.749 total contributions since 2006

Please don't contact me. I won't answer questions.

#### John D'Errico's Badges

View all

Contributions in
View by

pca versus princomp diferences in signs of coeffs (loadings) for cities dataset
The vectors generated are not unique to within a sign change. They can arbitrarily change sign, and nothing matters. (Not just o...

etwa 9 Stunden ago | 0

generate a random path between two points
This should be pretty easy. Use the graph theory tools in MATLAB. You can find them by: help graph The general algorithm is si...

etwa 9 Stunden ago | 1

Solve this matrix equation and find T
Homework, right? Why not admit it? Note that the solution, if one exists, is not unique, since IF T does exist to solve the pro...

etwa 12 Stunden ago | 0

exponentially distributed random number
Wow. Its been 40 years since I did this sort of stuff. ;-) I assume you have a stochastic process that you wish to model, as th...

etwa 18 Stunden ago | 1

| accepted

using the mod function to create and even random number generator in matlab
Why do you need the mod function? Just generate random integers, and then MULTIPLY THEM BY 2.

ein Tag ago | 0

Newton's Method in Matlab
First, consider if you are trying to solve the wrong problem. In your question, you state it as e^2*sin(x) - x = 0 However, in...

ein Tag ago | 0

| accepted

getting error while trying to write a code to solve general case diagonal Ax=b matrix
You should probably read the getting started tutorials, since you are using syntax that does not do what you think it does in MA...

2 Tage ago | 1

| accepted

8 nonlinear equations, 8 unknowns - little luck with fsolve/vpasolve
This same question gets asked on literally a daily basis. The problem is not fsolve. It lies in understanding nonlinear equation...

4 Tage ago | 0

I have a problem. It can not run. Help me please.
When you say only that something does not run, then tell people what was the error message. Show the COMPLETE error message. Thu...

4 Tage ago | 1

How to divide a distance into some equal parts?
You have two points. Call they xy1 and xy2, where the xy are row vectors of length 2. For example... xy1 = [-1,3]; xy2 = [2,5]...

4 Tage ago | 0

Replace the empty output of find() by the closest element
You are trying to use the wrong tool (i.e., find) to solve this. Well, you could use find, I suppose, with some significant effo...

5 Tage ago | 4

| accepted

Calc of mean and standard deviation
It should look like what photo? The mind reading toolbox has never gotten past beta testing state, and the copy I have is full o...

6 Tage ago | 0

How do I obtain the derivatives after interp2 with the 'spline' option?
interp2 does not return derivative information at the interpolation points. If you want to generate that at some general interp...

6 Tage ago | 0

fminsearch for fitting a function to experimental data
Even after you fix the problems in multiplication, let me look at your model and your data. syms c2 k12 k2e t fun = 120*c2*k12...

7 Tage ago | 0

Symbolic solution trigonometric equation
Why not try it? syms a b c x >> xsol = solve(a*sin(b*x) + sin(c*x) == 0,x) Warning: Unable to find explicit solution. For opt...

8 Tage ago | 0

How do i calculate these 3 unknows in these Equations
Easy enough. syms a b c x y z EQ(1) = a^2 + b^2 + a*b == x^2; EQ(2) = b^2 + c^2 + b*c == y^2; EQ(3) = a^2 + c^2 + a*c == z^2...

8 Tage ago | 1

| accepted

How to create a best fit line for data with an aymptote?
It partly depends on your goal. Do you just want to best estimate the constant asymptote? Or, are you looking for some function ...

9 Tage ago | 0

selection of n disticnt vector
Easy enough. A = 1:10; index = randperm(10,6); a = A(index(1:3)); b = A(index(4:6)); Since randperm generates samples witho...

10 Tage ago | 0

how do I write variance in percentage?
A percentage of what? Percentage always implies you are comparing one number to another. That is, suppose you have some variable...

10 Tage ago | 0

Can I update a toolbox without updating Matlab?
Short answer: No. Long answer: Nnnnnooooooooo. Why not? You can't do it, because then the versions would not be consistent. Ju...

10 Tage ago | 0

| accepted

Matlab implementation of AlphaZero
Now that I have some free time... I'm pretty sure the answer is no. Alphazero is a tool that was developed that could learn g...

11 Tage ago | 0

scatter3 error i not understand
Hmm. It took me a minute to see what the answer was from the error that was generated. scatter3(X,Y,Z,P) Error using scatter3 ...

11 Tage ago | 1

How can I write a function for this
Use plotregion, found on the file echange. https://www.mathworks.com/matlabcentral/fileexchange/9261-plot-2d-3d-region Note th...

11 Tage ago | 0

Getting the linear portion of a non-linear curve
As is often the case on a question like this, you have been too vague for us to comprehensively understand what you do "have". (...

11 Tage ago | 2

rotating this curve 20degrees
I would normally ask why not try it yourself, but I realize there are some issues that can easily catch you here. H = plot(t,sd...

12 Tage ago | 2

Why 4.8/1.6 is not equal to 3?
While there has been a lot of good discussion in the other answer, let me add a few points. When you type 4.8 in MATLAB, does ...

14 Tage ago | 1

How can I solve linear equation system in parallel?
You already are doing that! That is, decomposition uses all of the cores you have available for large problems. Watching my ac...

15 Tage ago | 1

| accepted

How can I get confidence intervals when the Jacobian matrix has an almost zero vector?
This is probably not a failure of the assumption of Gaussian arrors, though that may indeed be the case too. I cannot know. Wha...

15 Tage ago | 0