# 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**

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...

1 day 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...

4 days ago | 1

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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,...

4 days 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...

4 days 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...

5 days 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 ...

5 days 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...

6 days 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...

7 days 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 ...

8 days 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...

8 days 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...

9 days 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...

9 days 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 ...

9 days ago | 1

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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...

10 days 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...

11 days 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...

11 days 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...

12 days 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...

12 days 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...

13 days 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...

14 days 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...

14 days 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...

15 days 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...

15 days ago | 0

matrix, where each element is a column vector

You don't need a cell array at all! Just use a 3-d array. A = randn(11,7,1001); Now to compute the max in each vector, just u...

15 days ago | 1

inverser la matrice tri-diagonale

As much as I hate the suggestion, you could trivially use inv. ;-) Better would be to use sparse matrices. That is, learn to us...

15 days ago | 0

Solve long matrices equation

This is a classic algebraic Ricatti equation. https://en.wikipedia.org/wiki/Algebraic_Riccati_equation How do you solve it in ...

15 days ago | 0

fminsearch doesn't converge to the right value

These things are always easier than you think. Well, except when they are just as hard as you think. ;-) First, I'll create x a...

16 days ago | 1

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How to use a variable from script in a function that is in another script

Just create your function like this. In my example, k3 and m3 will be assigned, so that you can see how it works. k3 = 3; m3 =...

17 days ago | 0

How do I lower an image quality?

There are other ways to lower image quality. Several ideas have already been mentioned. Resize the image, then expand it back u...

17 days ago | 1

I am struggling trying to figure out this code I have it completed but I keep getting errors, can you help?

I need to laugh (sorry, but it is true) every time I see someone claim they have completely written a long piece of code, and cl...

18 days ago | 0