# 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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Support with interpolation using interp3 in MATLAB

And ... your question about MATLAB is? Far too much vague verbiage to know what is the problem. If you want to know how to use i...

circa 3 ore fa | 0

Ode45 g and dg

You cannot use the variable dg4, before it is defined. And we see you do this: dg2=m*A+k*g(1)+h1*k*g(3)+dg4 ... dg4=h1*k2x*g(...

1 giorno fa | 1

fitting with custom equation

(I assume you intended to write 1/y, and not I/y, where the variable I is not defined.) y = [1.6E5 2.5E5 4.1E5 8E5 1E6 2E6 7E6 ...

2 giorni fa | 1

improve fit compared to R

x = [0.858734025700000 0.975248753121875 1.02525125312812 1.13140821289062 1.15927407430000 1.18768630564687 1.21665290240...

3 giorni fa | 1

Some .jpeg photos can not be processed by Matlab code.

I've not even looked at your code. But you have jpg images, uint8 code values. So I wonder if adding the code values caused an o...

4 giorni fa | 0

Finding concave hull around abstract shape

I don't know the soure of this data. But, can you start with the two pieces as separate entities, form polyshapes from each, and...

4 giorni fa | 1

Numerical Integration MATLAB vs Python/VBA

This is difficult to say, because we know virtually nothing. First, does the problem arise from the use of subtly different da...

5 giorni fa | 0

Warning: Explicit solution could not be found./ empty sym

Does an analytical solution exist for EVERY equation you can write down? (No.) Even if such a solution does exist, is it certain...

6 giorni fa | 0

fmincon is not converge

It is very rarely easy to know why a solver fails to converge on a messy thing like this. But you should never let it come to th...

6 giorni fa | 0

Is there any way to perform an at least partially symbolic smulation (using ODE or discrete model) in simulink?

Essentially, no. This is a frequent question about tools like ODE45 too. Simulink is a purely numerical tool, like ODE45 and oth...

8 giorni fa | 0

d solve command matlab

syms e P S A t m V0 t0 V(t) real The point being that assumptions can apply only to variables, not functions. V(t) is a functio...

10 giorni fa | 0

Plotting data dependent on three independent variables.

Do you have a 4-dimensional holographic monitor? That is, you can plot things in 3-dimensions. You will see a projection into a ...

11 giorni fa | 0

vector output of a symbolic vector

syms s X Y Z l1 = X*s - 1 == 3*X + Y + Z + 2/s l2 =Y*s == - X - Y - 1/s^2 l3 =Z*s - 2 == X - Z - (s - 1)/s^2 [Xsol,Ysol,Zsol...

11 giorni fa | 0

Optimisation of three function in two variables

There may be an issue here, if you think you can maximize them all simultaneously. The (x,y) coordinates that maximizes one func...

13 giorni fa | 1

About fitting one curve with one equation and calculating two values from fitting

Suppose I gave you a set of data, and asked you to tell me two parameters from the data. All I need is one data point, More woul...

14 giorni fa | 0

How to fit this model with a Weibull distribution?

If this is data that you think comes from a Weibull, then you do not want to use regression techniques to fit the distribution. ...

17 giorni fa | 0

how i can show in matlab tha sqrt(x^2)=x in symbolic toolbox

Except, that equality does NOT hold! The sqrt "function" has two branches. sqrt(x^2) can as easily be -x, as it is x. So you can...

22 giorni fa | 1

I keep getting 4 answers per variable in 4x1 sym

L = 225; % Length of the ship in meters B = 32; % Beam of the ship in meters T = 12; % Draft of the ship in meters v = 0.5; %...

24 giorni fa | 1

Find zero of simple monotonic function where the independent variable can only be integer

@Michael Albert No. You just THINK there is some obscure MATLAB function to solve your problem. You do not know that to be the ...

24 giorni fa | 0

Why is my test accuracy higher than validation accuracy?

Not really. It might be a reflection that you needed more data, that your sets are just not large enough. The law of large numbe...

24 giorni fa | 0

| accettato

What is happening with the line of best fit here?

StrainStress = [0.00005 010.1; 0.00007 014.3; 0.00011 021.8; 0.00014 027.6; 0.00020 040.0; 0.00030 061....

25 giorni fa | 1

| accettato

Generating a matrix of 0s and 1s with constrained domains

Are you saying you want to break the matrix into a set of regions, where within the region, the matrix contains zeros, and the r...

26 giorni fa | 0

How to provide a positive and negative value for the tolerance value?

Good answer by @Voss of course. I'll merely add a few points of interest. You could just test to see if the current term being ...

27 giorni fa | 1

Finding out lengths of sequences of numbers in a set of vectors

It took a few seconds staring at the output you expect to see, and realize what you meant. I THINK the first element in each row...

27 giorni fa | 1

Is there a premade file regarding a verification test to see if there is any issues with the installation?

Is there anything that will test every line of code in MATLAB? Every toolbox you have purchased? No. Not that is given out to yo...

28 giorni fa | 0

I have a question relate to Gauss seidel method

Updating the vector x (small x) and then looking to see if the vector X (capital X) is converging seems like a bad idea. You did...

28 giorni fa | 0

integral using "int" function

Not everything you write down will have a simple, algebraic solution. As much as people seem to think they are, computers are no...

29 giorni fa | 0

f(x) = x^2/3(3-x^2)(x-4). How do I enter this function in MATLAB?

How do you enter it? You already did exactly that, at least in symbolic form. syms x real % f= input('Enter the function f(x):...

30 giorni fa | 0

Very large output numbers

syms Kc s X = (6982830709666455*Kc*s)/140737488355328 vpa(X,10) So here, 10 digits shown.

circa un mese fa | 0

atan2 does not accept complex numbers as input

It seems the answers provided so far are missing the point. If we want to see a 4 quadrant atan2 version, that works for complex...

circa un mese fa | 1

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