John D'Errico

Retired

Last seen: Today | 2006 以来アクティブ

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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How to sub sym to a number in a matrix
syms x y z M = [x-2,x+y,z^2] subs(M,[x,z],[1 3])

2日前 | 0

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Can the function "Taylor" process the input type "Function handle" directly?
Can taylor handle some completely general function handle? No. Why not? A Taylor series is easy to compute, in theory. The coef...

2日前 | 0

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how to take numerical inverse integration?
This is technically called an inhomogeneous Fredholm integral equation, of the first kind. https://en.wikipedia.org/wiki/Fredho...

2日前 | 0

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How can I find all n-bit semiprime numbers?
Ok, I'll give in. A reasonable question, with a reason to be asked. Given a valid reason for the question, I am actuually quite ...

3日前 | 0

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generate a random number base on pdf function
First, is that the PDF of a random variable? If it was, the integral would be 1. syms x P_x = x/2 + 1/2; int(P_x,-1,1) And o...

3日前 | 1

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Can we choose step size rule in fmincon?
If you could control the stepsize, then it would damage the convergence properties of a tool like fmincon. Sadly for you, this i...

4日前 | 0

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Describe a colormap in the legend of a plot
Hard to put it into a legend, since legend is not designed to do that. Far easier (one line of code) to just put a title above t...

4日前 | 0

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An example of a large matlab project
Look on the file exchange. You will see many such submissions. I have at least a few such, with at least one where I spent multi...

5日前 | 0

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Rate of Change - Derivative of experimental data
If your data is smooth enough, then the direct gradient calls that Star shows are ok. The problem is, if there is any noise in y...

5日前 | 0

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I did not get any email for activation key. My recent purchase order is complete.
Answers is not customer support. Answers is a volunteer forum. we have no ability to help you. We have no access to any database...

5日前 | 1

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Putting one matrix a varying number of times along the diagonal of another matrix
A = rand(3); n = 50; Acell = repmat({sparse(A)},[1,n]); B = blkdiag(Acell{:}); spy(B) Note that I made A sparse in there, s...

5日前 | 0

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How to use File exchange
It does not matter that you use a mac or not. Save the top level folder on your search path. So use pathtool or addpath. Then sa...

5日前 | 0

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Hello, I did a for loop but my friend told me it is not the correct matlab syntax. Can anyone help me the for loop is in the description below:
for xa=1; This is not a loop. It does nothing but assign the value 1 to the variable xa. NOTHING. No loop. Instead, it looks l...

5日前 | 0

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Output Symbolic Trig Math in Degrees
If you use cos and sin, terms like this are meaningless, if the 90 is a number in degrees. Well, let me just say you will get me...

7日前 | 0

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out of memory error
Um, 1e20 rows? Seriously? Do you have that much memory? Clearly not, since your computer is throwing up at an 1e8 by 27 array. E...

8日前 | 3

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How to numerically integrate the planar equations of motion?
You need to learn how to write a function handle. What you wrote was incorrect syntax. Do you see the spare comma, AFTER the par...

8日前 | 1

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Converting to scientific notation in matlab
We are not a "team". We are just a number of people who act as complete volunteers, individually. You cannot "represent" it tha...

8日前 | 0

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Why the result in curve fitting tool shows a different graph in plot?
@Hao Tu (This is only a followup, and since you already understand the issue, merely a clarification to Steven's accurate answe...

8日前 | 1

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What is the difference between backward slash vs forward slash in MATLAB?
BOTH of them are linear algebraic solutions. Where matrices are involved, they solve subtly different problems. A\b solves the ...

9日前 | 2

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Fmincon makes an extremely big jump in parameter search
I think you do not understand how an optimization tool works. Those first calls to your objective are there to differentiate it...

9日前 | 0

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How to smoothen a plot?
Simple. Delete the points in the beginning of the curve that give you the spikes. WTP? They will be easy enough to spot, as they...

9日前 | 0

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How to write code for Assignment problem using GA matlab tool.
Does GA allow you to specify that some variables are integer? (Yes.) Does GA allow you to specify lower and upper bound limits ...

10日前 | 0

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Solving a System of Trig Equations
If the only unknown is theta1, then what is y? If you actually have a value for y, then you have two equations in one unknown v...

10日前 | 0

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Solve Equation and Plot it
Easy peasy. Essentially one line of code once you define the various constants. syms f_1 f_2 alpha = 0.4207; skalar = 4.5375;...

11日前 | 0

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Declrarion of an array using tilde (~). what is the correct way of using it, because my code prompts me incorrect use of tilde.
This is a test: if i == D(k) It is the correct way to use == because == is a comparison operator. However, this other line is...

12日前 | 1

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Methods to create arrays of NaN
A NaN is a nan. A NaN by any other name, is still just a NaN. But there are faster and slower ways to make them, and surely the...

13日前 | 0

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maximization problem , fmincon optimization
syms x y objxy = ( -.858*x-.04182*y-1.645*sqrt((.5882*x -.055*y).^2 + (-.0558*x +.352*y).^2 )); If x+y == 1 then we can replac...

15日前 | 1

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How can I plot f(x,y) in xy plane
help fsurf

18日前 | 0

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Should we always search for the global minima in our optimization problem?
Yes. And, no. Amazing how the anwer is often, well, it depends... You do want to find the true global min. Yes, that makes sens...

19日前 | 0

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Find smallest Eigenvalue and the corresponding eigenvector.
Just compute the matrix Ainv = inv(A); Now use your code on the matrix Ainv. This works because the smallest eigenvalue is no...

19日前 | 1

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John D'Errico

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