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John D'Errico


Retired

Last seen: Today Attivo dal 2006

Followers: 7   Following: 0

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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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Risposto
Curve Fitter Polynomial Plots Strangely In Script
CONGRATULATIONS! You win an award for the one millionth person to make this mistake! Your award is a free trip to the fabled vac...

circa 7 ore fa | 0

Risposto
Why is indexing a sparse matrix not behaving how I would expect?
This is not a question about sparse matrices. Well, it is, but it is not really. Sparse matrices are exactly the same as any oth...

circa 7 ore fa | 0

Risposto
how to write the right code to measure the elapsed time of this method d1 = diag(1./diag(A))
Why do you care? The computations will be almost inifinitessimal, even for a huge matrix. (Do you understand the notation O(n)?)...

1 giorno fa | 1

Risposto
Alternative to interp2
Perhaps you are calling interp2 multiple times in a loop, when a single call with multiple points will be far faster. This would...

3 giorni fa | 0

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How can people who are bad at math and have no programming aptitude learn MATLAB? (Long question)
An old question, one that surely would be better placed in a discussion, now that we have them. However, as soon as someone dec...

6 giorni fa | 0

Risposto
Someone that works with symbolic variables?
When k is even slightly large (apparently 4 is large enough) things go to hell. Did I not answer this question before? I know I ...

6 giorni fa | 1

Risposto
using polyval with one of the polynomials of a spline obtained with the unmkpp command, the results do not overlap! Why?
@David Goodmanson and @dpb and @Steven Lord have all said the polynomial segments are intended to be LOCAL with respect to the b...

6 giorni fa | 0

Risposto
Problems with code with symbolic variables.
No. I won't consult by gmail, or whatever. But there is no need. Even for k==2, what do I see? eqn = [3*c1^2 + 3*c3 == 0, 3*c...

6 giorni fa | 0

Risposto
MATLAB Programming Techniques, Extracting Portions of a table
Why do you need it? Well, I don't see the question in the course, and I am not enrolled in the course, so... But what does that...

7 giorni fa | 0

Risposto
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...

7 giorni fa | 0

| accettato

Risposto
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...

7 giorni fa | 2

Risposto
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...

11 giorni fa | 0

Risposto
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...

12 giorni fa | 1

| accettato

Risposto
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...

12 giorni fa | 1

Risposto
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...

12 giorni fa | 0

Risposto
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...

13 giorni fa | 0

Risposto
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. ...

13 giorni fa | 0

Risposto
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...

14 giorni fa | 0

| accettato

Risposto
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'...

14 giorni fa | 0

Risposto
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 ...

15 giorni fa | 0

| accettato

Risposto
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...

17 giorni fa | 0

| accettato

Risposto
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 ...

17 giorni fa | 0

Risposto
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...

19 giorni fa | 0

Risposto
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...

20 giorni fa | 0

Risposto
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...

20 giorni fa | 0

Risposto
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...

21 giorni fa | 0

| accettato

Risposto
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...

22 giorni fa | 0

Risposto
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 + ...

23 giorni fa | 0

| accettato

Risposto
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...

25 giorni fa | 0

Risposto
[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...

25 giorni fa | 2

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