# John D'Errico

### Retired

Last seen: Today Actif depuis 2006

Followers: 3   Following: 0

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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Syntax for specifying boundary condition using dsolve.
Your beam is fixed in position at the left end, as is the slope at that point. At the right end, you have fixed the location, b...

environ 5 heures il y a | 1

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How to use fminsearch for vectors
I think your problem is you are confused. And your confusion turns into a highly confusing question. Questions like is the optim...

environ 11 heures il y a | 0

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How to Reduce Oscillations (not noise) in a Signal?
To me, the upper signal looks like the convolution of something like a sinc with the lower signal. And that would mean, IF you k...

1 jour il y a | 0

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How to find the intersection of linear regression model and yline
Pretty boring data. T(:,1) = [0 1 2 3 4 5]; T(:,2) = [0 1 2 3 4 5]; P = polyfit(T(:,1),T(:,2),1) a = P(1) b = P(2) They...

1 jour il y a | 0

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Issue with solving ill-conditioned DAE system on MATLAB 2023b
You have a DAE, with a linear constraint system that happens to be ill-conditioned. I would try reducing the constraint system. ...

2 jours il y a | 0

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inv(A)*B*inv(A) or A\B/A, which is more accurate for a full rank A and half rank B
Why would you want to compute the inverse of A TWICE ANYWAY? Even using both slash and backslash is arguably a bad idea, since a...

2 jours il y a | 0

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Finding accurate inverse of binary circulant matrix
Gosh. I thought that multiplying a matrix by its inverse gives an identity matrix. :) A = readmatrix('MixingLayer.xlsx','sheet'...

3 jours il y a | 0

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Doing a Matlab update without charging
Is it a bad thing? Only in the sense that if your computer suddenly dies in the middle, the software may now be in a spot where ...

3 jours il y a | 0

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Not able to plot a proper graph for the equation.
syms x y = (1*1*((25)-(x.^2)))/((x.^4)-((x.^2)*((1*(1.78))+(25)+1))+(1*(25))) First, where are the poles? A pole lives where t...

6 jours il y a | 0

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How to find solution to system of 2 circle equations in Matlab?
Torsten has answered your question perfectly well, I think. No solution exists for that problem as posed. But suppose you had a ...

6 jours il y a | 0

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How to colour a portion of a curve by red and remaining by black
Plot it as TWO curves, both on the same figure, one in red, one in black. Use the hold command between the two calls to plot, s...

7 jours il y a | 0

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Solve an ODE on a torus
Simple enough. Just transform the problem. So if [u,v] live on [0,1]x[0,1], then s = (cos(2*pi*u)+1)/2 t = (cos(2*pi*v...

8 jours il y a | 0

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Problem with matrix dimensions
I'm not sure why you would use a Newton method to solve what solve will do directly, in an apparent algebraic form. beta1 = 0.0...

8 jours il y a | 0

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Solve ill-conditioned linear systems
The determinant of a matrix is completely, totally irrelevant. Yes, I know you were taught that if it is zero, then the matrix i...

9 jours il y a | 0

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I fail to see the issue. No, you cannot adjust how a convex hull computes the area. A convex hull does not see pixels. It sees t...

10 jours il y a | 0

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How to calculate real roots of a polynomial equation under square root ?
syms t real coupler_parametric=[5163136522924301/2251799813685248,... 2^(1/2)/2 - (8*t)/(t^2 + 1), - (4*(t^2 - 1))/(t^2 + ...

11 jours il y a | 0

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Find approximate solution of equation
Is there some general method, to ALWAYS be able to approximate the solution of a large system, and have a reliable result? No. O...

13 jours il y a | 0

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[0:0.1:1] whys is not exactly 0.1 steps ?
Can you represent the number 0.1 exactly? Remember that MATLAB does not store the exact representation of numbers. Instead, it u...

14 jours il y a | 2

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How to stop quadratic formula calculator from giving inverse outputs?
The roots of the quadratic you supply are indeed 6 and -3. roots([1 -3 -18]) So your code worked correctly. If you expected ...

14 jours il y a | 1

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hyperpca applied to a set of several hyperspectral images
You cannot combine multiple PCA analyses. Since each one requires the computation of the eigenvalues and eigenvectors of a matri...

14 jours il y a | 0

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Simpson integral - problem with writing the formula
a is a scalar. At least, it should be, based on how you show the code was called. If so, then why have you done this? dI = f(a(...

15 jours il y a | 0

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If I have an array and I need to find an element in the array how do I go about it?
I think you are confusing things, not understanding there is a difference between the number 110, and the vector [1 1 0], and th...

16 jours il y a | 0

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Matlab Predict function is not efficient
No code is ever as fast as users want. If you know how to make it faster, then write your own version. If your version really is...

17 jours il y a | 0

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Equally spaced points along a nonlinear path
Simpler yet, just download my interparc from the file exchange. It allows you to do the operation in a variety of ways, using se...

18 jours il y a | 1

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Converting between x,y cartesian variables to angle in symbolic variables
No, the toolbox will never try to understand your equations, and then infer what the variables mean to you, and then perform sub...

18 jours il y a | 0

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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...

18 jours il y a | 1

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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 ...

19 jours il y a | 0

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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...

19 jours il y a | 1

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