# John D'Errico

### Retired

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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**Content Feed**

How can I get the symbolic steady state vector of a Markov Chain?

Easy, peasy. For example, given a simple Markov process, described by the 3x3 transition matrix T. T = [.5 .2 .3;.1 .4 .5;.1 .1...

약 13시간 전 | 1

How to extrapolate given data to find more number of points?

Your words ask how to do interpolation. However, then you ask about extrapolation. The two problems are VERY different. To quo...

1일 전 | 0

Array indices must be positive integers or logical values?

MATLAB does not allow an index of 0. The FIRST element of an array or vector is indexed as x(1). In your loop, what was the ran...

1일 전 | 0

MAXIMUM MATRIKS IN MATLAB

Since you did not say which one to leave non-zero, I'll asssume that all values equal to the maximum are retained. A = randi(20...

1일 전 | 0

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Backslash does not provided the solution with the smallest 2-norm

It seems the gist of your question comes down to the idea that for a wide matrix, MATLAB should (in your eyes only) always produ...

3일 전 | 0

Solving Trigonometric Equations with More Than One Variables

You need to understand that first, the use of solve like this will probably fail. You have 4 equations, but only 3 unknowns. Sol...

4일 전 | 0

I need an expression between two symbols R and a connected within a large order determinant.

Sorry, but not going to happen. Ever. Why not? There are multiple reasons why this will fail, so you are tilting at impossibly h...

5일 전 | 0

Function, dot, help me for solution

Your problem has NOTHING to do with dots. This is a common mistake we see made here. Suppose you have a pair of function handle...

6일 전 | 1

Equation to Matlab code

(I really hope I am not doing your homework here, but the question is not posed as if it is, even though I assume you are a stud...

6일 전 | 0

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How to get elapsed time of a code in matlab ?

Sorry, but no. A prediction of the time required for some arbitrary piece of code will never happen. It cannot happen. Well, no...

7일 전 | 2

Optimization of points generating inside a sphere

The common scheme that is advised is to generate points randomly, then if a point is too close to a neighbor, then you reject it...

7일 전 | 0

why covariance matrix Should be positive and symmetric in mahalanobis distance

SIGH. Multiplying a covariance matrix by its transpose is NOT what you want to do! If it is already a covariance matrix, that op...

8일 전 | 0

How do we interpolate a data set with noise?

Um, you generally don't want to interpolate noisy data! That is just a good way to amplify the noise. I did show many years ago,...

8일 전 | 0

n as the natural numbers

There are many ways to interpret this question. If the goal is simply to TEST to see if n is a natural number, then you might do...

8일 전 | 0

how to use surf function?

Almost always, when someone says they have a single vector of z values and they want to use surf, they mean that they have a lis...

9일 전 | 0

Is there an easier way to index diagonal elements of a matrix?

A = diag(randi(100,10,1)); n = size(A,1); A(sub2ind([n,n],[3 6 7 9],[3 6 7 9])) = 1000; A If you understand how matrix ele...

11일 전 | 1

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Symbolic solve with user-specified precision

Your belief has preciously little value. Faith in mathematics tends to be a waste of mental energy. Let me expand your equations...

11일 전 | 0

I created an array of size 255 of pseudo-random integers . I want to access the value at a particular index of the array how can I do it ?

Basically, you need to look at the getting started tutorials. Try the MATLAB Onramp. r0 = uint8(randi(255,255,1)); r0(158)

12일 전 | 0

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Is it possible to (non-linear) minimize x^y by choosing both x and y?

Can MATLAB solve it? Yes. Your doubt is only you not knowing how to solve the problem. In fact, simplest is to transform the pr...

13일 전 | 0

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isprime function seems to have poor performance

As a follow-up, I've also compared the MATLAB isprime to that of Python and Mathematica. On significanty large numbers, The MATL...

13일 전 | 2

Where to get a zip code for free 30 days trial

This is not a question about MATLAB. However, the answer is easy. CONTACT sales/customer service. Just contact the MathWorks dir...

14일 전 | 1

Is it possible to generate an encrypted function that can be used a limited number of times?

Is it possible? It depends on how good or technically naive are your users. How determined would they be? You can "encrypt" a f...

15일 전 | 1

Optimization - find a max on a complicated function

You maximize a function using a tool that minimizes it, by finding the minimum of -f(x). How to do it? Use fminbnd. Set the bou...

16일 전 | 1

finding the orthogonal vectors for a series of vectors

I think you are confused. Really, this is not a difficult problem. You need to understand the linear algebra of it, or you will ...

16일 전 | 3

How to select columns in a matrix whose first row data is positive?

Easy peasy. A=[-1 2 5 4 -4;1 2 3 4 6] B = A(:,A(1,:) > 0)

18일 전 | 0

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How can I use the ( nchoosek ) for this case nchoosek(x,y) where x=[1:1:80] , and y=64;

As Jan pointed out, you CANNOT solve your problem in this way. Using nchoosek in this form, it almost always is a form of brute ...

19일 전 | 0

How can i solve this differential equation by the method of finite difference approche?

Answers is not a service where we do your homework assignments. However, you have now gotten an answer, so I'll point out that y...

19일 전 | 0

Decimal and very small values returning zeros

Um, why are you doing this numerically at all??????? With the variable of integration as c, your kernel is: (pi*t)^(-1/2).*...

19일 전 | 0

least square fitting for a nonlinear regression.

You show no data, and only a difficult to understand equation, but I am pretty sure what form you are trying to fit. y(t) ...

20일 전 | 0

How to solve a system of equations?

pt1, pt2, and pt3 are the equations of the surfaces of three spheres, each wih the same fixed, but unspecified radius. Pick an...

20일 전 | 0