# John D'Errico

### Retired

A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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**Feeds**

how write a matrix with specific features

I think you are confused about what you can do with MATLAB. Those constraints simply tell you the associated matrix for the grap...

ungefär 4 timmar ago | 1

I have a nonlinear equation with a symbolic variable and cant solve it.

Look carefully at your problem. n = 2.1; alpha0 = 0; syms p alpha eqn = p^(n+1) - alpha0*p^n + p -(alpha0 + alpha) == 0 So ...

ungefär 21 timmar ago | 0

| accepted

findging eigenvectors with eigenvalues

Most of the time when I see someone worry their eigenvectors are not correct, it is just because of a sign error on the eigenvec...

en dag ago | 1

Library function log10 not found when using fit

x = rand(10,1);y = x + rand(10,1); fit(x,y,'log10') It is almost always, ALWAYS the case that when this happens, you were prev...

3 dagar ago | 1

| accepted

iterative estimation of eigenvalues and eigenvectors by the inverse power method. Your MATLAB/Octave code shouldn’t be hardcoded. ● Calculate the eigenvectors and eigenvalues

Let me guess, you have a problem with this matrix. Does the matrix have any special properties? What, for example, are the eige...

4 dagar ago | 0

using PCA to filter outliers in MATLAB

I've attached my quick shot at an n-dimensional outlier tool, based on Mahalanobis distance. I am pretty sure it has some seriou...

5 dagar ago | 1

| accepted

How do I plot a symbolic equation that I have created?

By the way, there is NOTHING symbolic in the code you wrote. syms t % this makes t symbolic % no need to put decimal points ...

6 dagar ago | 0

scatter command not working

(It is good you are using the tutorials.) But first, learn to read the error message, an important skill in using MATLAB, unless...

8 dagar ago | 1

| accepted

Nonlinear optimization with branching solution space

Just solve 11 distinct problems, each of them continuous. Use a loop, setting x to each of the 11 possible values. Save each sol...

11 dagar ago | 1

| accepted

how to create nxn matrix with main diagonal that enters odd rows/columns with zero and even ones start with 2(n+1) sequence

Simple is to use diag. n = 5; % Now many non-zero elements will we have? N = 1:(2*n); % a simple index vector D = N.*mod(N-1,...

11 dagar ago | 0

Does I properly translate the equations in matlab code?

Ouch. That would be a miserable set of equations to try to code. (You have my sympathies.) I did some very quick spot checks, an...

11 dagar ago | 0

problem in curve fitting

C1 continuous? Is there a difference? Absolutely YES. C1 continuity, using circular "arcs" in 3-d? UGH. I'm a career mathemati...

12 dagar ago | 0

species go to negative values

Remember that the software does not truly understand your model, and what you are attempting to simulate in that model. It only ...

12 dagar ago | 0

Better "probabilities"?

How effective is rand? I'm not sure what you mean by "effective", or for that matter, "advanced". It is a state of the art rando...

13 dagar ago | 1

Need help solving heat equation using adi method

You say it works for sufficiently small values dt. With that exp(t) term in there, do you seriously expect it to work well for...

14 dagar ago | 0

Non-linear Algebraic 36 equations unsloved

Actually, a starting value set like ones(36,1) is often a dangerous thing to do. Making all of the starting values the same can ...

15 dagar ago | 0

math model of neural network fitting

As is often the case with such "models", there is nothing you could write down, at least not easily, and without nasty arrays of...

15 dagar ago | 0

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About Fluid dynamics in a porous medium...

As @Torsten said, this is far too vague a question. I would suggest starting with a far simpler problem, especiially good is if...

16 dagar ago | 0

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inversing huge Y Matrix

As always, I'll start by saying that computing the inverse of a matrix is a bad idea. And of course, you don't say what you thin...

16 dagar ago | 0

How can I solve this implicit function in MatLab?

Trivial, in some eyes. ;-) This is one of the simpler implicit problems you might write down, since a direct solution exists in ...

16 dagar ago | 1

| accepted

How to add unknow parameter in matrix and solve it by use det() syntax for finding w

syms w; m1 = 1.8; m2 = 6.3; m3 = 5.4; m4 = 22.5; m5 = 54; c2 = 10000; c3 = 500; c4 = 1500; c5 = 1100; k2 = 1*10^8; k3...

17 dagar ago | 0

solving linear systems of equations

A long forgotten question and one with an answer that may not be appreciated by @Chloe St John, given that multiple questions by...

18 dagar ago | 0

MathWorks Administrator Account Privileges

Contact customer support at MathWorks. That is not Answers. We cannot help you directly. https://www.mathworks.com/support/cont...

18 dagar ago | 0

When integrating acceleration do you need to convert velocity?

When you keep on subtracting off the mean, you do strange things to the result. But you need to consider what a constant of inte...

19 dagar ago | 0

How to efficiently solve a system with an infinity number of solutions?

Note that a solution need not always exist for all n. When n==1, and so A is a 1x1 matrix, it is completely known. So unless yo...

19 dagar ago | 0

How can I calculate the integral of Legendre function P(n,theta) ?

@Shreen El-Sapa I think you do not understand that a Legendre polynomial is meaningless over some other interval. It has no spe...

20 dagar ago | 1

Create a matrix and a map of Hydrologic Soil Group values using integer or character values

MATLAB does indeed allow you to produce a character matrix, with those characters. However, I assume you have scattered data, wi...

21 dagar ago | 0

Determine row vector out of matrix with most evenly spaced and distributed values

Simple. Sort of. But you need to define what equal spacing means to you, and how you will measure the deviation from equal spaci...

21 dagar ago | 0

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Are polyshape vertices preserved reliably without floating point errors?

Um, probably, yes. But potentially no. Yes, because on most operations, you will just be indexing into the original set of vert...

22 dagar ago | 1

Integrate function by for loop

As always look carefully at your code. Learn to use the debugger. It would tell you the problem, and in which line there was a p...

22 dagar ago | 0