# John D'Errico

### Retired

Last seen: Today Active since 2006

Followers: 5   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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I want show population on plot like 36M, 37M....
You want the plot to plot each point as a string like 36M, 38M, etc? Why not just divide by 1e6, then use the axis label to ind...

5 days ago | 0

Why are the components of the two eigenvectors not continuous and smooth, when the underlying data is continuous and smooth?
You can think of the eigenvalues (and assiciated eigenvectors) as coming from the roots of a polynomial. In fact, they do exactl...

5 days ago | 2

How to interpolate values given a starting and end point
If you ONLY have two data points, the only possible interpolation is LINEAR. There is no fancy method to interpolate in a nonlin...

8 days ago | 0

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...

9 days ago | 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...

9 days ago | 1

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...

10 days ago | 0

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...

10 days ago | 0

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. ...

11 days ago | 0

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...

11 days ago | 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'...

12 days ago | 0

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 ...

12 days ago | 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...

15 days ago | 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 ...

15 days ago | 0

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...

16 days ago | 0

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...

17 days ago | 0

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...

17 days ago | 0

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...

18 days ago | 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...

19 days ago | 0

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 + ...

20 days ago | 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...

22 days ago | 0

[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...

22 days ago | 2

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 ...

23 days ago | 1

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...

23 days ago | 0

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(...

24 days ago | 0

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...

25 days ago | 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...

26 days ago | 0

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...

27 days ago | 1

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...

27 days ago | 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...

27 days 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 ...

28 days ago | 0

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