# 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**

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...

4 giorni fa | 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...

4 giorni fa | 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...

7 giorni fa | 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...

8 giorni fa | 1

| accettato

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...

8 giorni fa | 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...

9 giorni fa | 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...

9 giorni fa | 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. ...

10 giorni fa | 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...

10 giorni fa | 0

| accettato

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'...

11 giorni fa | 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 ...

11 giorni fa | 0

| accettato

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...

14 giorni fa | 0

| accettato

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 ...

14 giorni fa | 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...

15 giorni fa | 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...

16 giorni fa | 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...

16 giorni fa | 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...

17 giorni fa | 0

| accettato

Adjusting Convex Hull Area

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...

18 giorni fa | 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 + ...

19 giorni fa | 0

| accettato

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...

21 giorni fa | 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...

21 giorni fa | 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 ...

22 giorni fa | 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...

22 giorni fa | 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(...

23 giorni fa | 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...

24 giorni fa | 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...

25 giorni fa | 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...

26 giorni fa | 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...

26 giorni fa | 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...

26 giorni fa | 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 ...

27 giorni fa | 0

| accettato