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John D'Errico


Last seen: ein Tag ago

Retired

5.570 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
While loop with power.
This is the discrete logarithm problem. https://en.wikipedia.org/wiki/Discrete_logarithm#:~:text=Modular%20arithmetic.%20One%20...

etwa 15 Stunden ago | 0

Answered
How to pseude-randomize dataset with constraints
So, you want it random, but you don't really want it random, in a sort of vague, unspecified way. Can you do this in MATLAB? NO...

etwa 22 Stunden ago | 0

Answered
How to calculate the volume of a segment of spherical cap intersected by a plane ?
I did suggest this scheme in my response to your question. And it seems pretty easy to do, so I am not sure where the problem li...

ein Tag ago | 0

| accepted

Answered
Array indices must be positive integers or logical values
The problem lies here: for i = 1:N za(i) = (z(i+1) - z(i-1))/(2*h); end When the loop starts out, what is i? i is 1, ri...

4 Tage ago | 0

Answered
Help fitting data to an implicit equation
My thought would be the lazy solution. If your model is: ((1-y)^(1-b)/y)=exp(-kt) then log the model. That is, we know tha...

5 Tage ago | 0

Answered
How can I interpolate between my original endpoints with cscvn?
I think you do not understand splines. (Not uncommon.) Splines have the property that they can produce results that lie outsid...

5 Tage ago | 0

Answered
Function fitting on a set of data points
What did you do wrong? It looks like Jon may be correct, in that you did not use the newly estimated set of parameters from the ...

6 Tage ago | 0

| accepted

Answered
Question About Number Format in MATLAB Command Window
These are numbers from the symbolic toolbox. That toolbox does not use the format tools to display numbers (though perhaps argua...

6 Tage ago | 1

| accepted

Answered
How to Use "Ask a Question" Section Correctly?
It looks like this is a (surely quickly fixed) bug in the site itself. They recently made some changes, allowing users to use ...

6 Tage ago | 1

Answered
Precision (decimal digits) are very low and digits(32) does not help.
Of course, asking for 32 or more digits of precision is a bit on the side of the ridiculous, when the numbers going into the com...

7 Tage ago | 0

Answered
how do i download the function kstest_2s_2d?
You click on the link that says download, from this page. https://www.mathworks.com/matlabcentral/fileexchange/38617-kstest_2s_...

8 Tage ago | 0

Answered
array and inverse tan
I think you do not unerstand MATLAB. I'd start with taking the Onramp tutorial. atand of what? atand is a FUNCTION. You need to...

9 Tage ago | 0

| accepted

Answered
for loop help - Newton's method
I agree with much of what David has written (except for one thing). If you wish, feel free to accept his answer, as long as you ...

9 Tage ago | 0

Answered
Aerofoil graph interpolation/extrapolation
You lack sufficient information to construct a meaningful surface, since you have only 2 pieces of information in terms of Reyno...

9 Tage ago | 1

| accepted

Answered
how do i generate a torus?
WAY too much effort here to generate a torus. Start here: https://en.wikipedia.org/wiki/Torus [theta,phi] = meshgrid(linspace(...

10 Tage ago | 1

Answered
Using fminbnd on a Function with Multiple Outputs
Just evaluate your function one more time, after the optimization is done when you have the minimal location for x. This last ti...

10 Tage ago | 0

Answered
get several answers with solve
There is no analytical solution. syms x solve(cos(x)*cosh(x)+1==0) Warning: Unable to solve symbolically. Returning a numeric...

10 Tage ago | 0

Answered
Want to find exact answer for symbolic variable polynomial factorization
You say this is a polynomial. It cannot be a polynomial in c or n, since c and n live in the exponentis of p. Therefore you are ...

11 Tage ago | 0

Answered
Reduced Echelon form is wrong
A = [-2 2;-.4 .2]; [V,D] = eig(A) V = -0.974588432346814 -0.754384720454159 -0.224003097156669 ...

11 Tage ago | 0

Answered
Making complex number to trigonometric formula
Since this is clearly homework... Hint: what does angle do? (atan2 would also suffice, but then you would need to know how to e...

11 Tage ago | 0

| accepted

Answered
Find the volume under a 3D surface
Since this appears to be a gridded surface, then you can just use trapz, twice. Call it once on the x dimension, and once on the...

11 Tage ago | 0

Answered
How to contour this use matlab?
Are you asking how to write the code to take scattered data, and derive contours from pairs of points, using some variation of t...

12 Tage ago | 1

Answered
Generate random numbers in the second decimal point
Something like this is about the noise you want to see in that digit. If it is too large, then multiply by a little smaller numb...

13 Tage ago | 0

Answered
Error using betainc Z must be real and non-negative/polyfitn
You have 4 data points. You are trying to estimate a model with how many unknown coefficients? (20. Yes. 20.) I won't even get...

14 Tage ago | 0

Answered
How to find eigenvectors?
Why does V seem strange? A = [-2 0 2 2 -1 5 0 ...

14 Tage ago | 1

Answered
How to define a variable without using syms ?
fun = @(lambda) det(A - lambda*eye(size(A))); fun is a function of the unknown variable lambda. It is a function handle. It has...

15 Tage ago | 0

Answered
null(Matrix) returns an empty vector
That null returns an empty vector merely means your matrix is full rank. You cannot compute a non-empty null space of a full ran...

17 Tage ago | 1

| accepted

Answered
solution giving me imaginary answers.. Help me with this.
To be more clear, equations 5,6,8,9 merely establish the value of y1,y2,T,A. eqn5= y1-0.6==0; eqn6= y1+y2-1==0; eqn8= T==318....

18 Tage ago | 0

Answered
proble with differential equation
What did you do wrong? You wrote this: dsolve(diff(diff(f))+3*diff(f)==12*x-5), f(0) == 1, Df(0)== 0 And how is that different...

18 Tage ago | 0

Answered
Matlab 2020b won't open on Mac OS Big Sur
The simple solution of course to resolve any problems is to use R2021. It seems to run nicely on Big Sur. That is, given we are ...

18 Tage ago | 0

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