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John D'Errico


Last seen: 1 day ago

Retired

5,743 total contributions since 2006

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

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Answered
How to fix this error “Index exceeds the number of array elements (57)” while using minboundquad function
That code was written so long ago, I forgot I ever wrote it. But also, it was written in the days when the convex hull and trian...

2 days ago | 0

Answered
matrix calculation for matrix
Simple. One line. No for loop. Nothing hard. B = A(10:10:end,:);

4 days ago | 1

Answered
Why this function infinity loop
Because if your powers grow larger than 2^53-1 (i.e., flintmax), the number is no longer expressable exactly as an integer. All ...

6 days ago | 0

Answered
why ga does not respect upper bounds ?
Um, ub = [40 1e6 1e6 1e6 1e4 1e4 9000]; numel(ub) I can count, but I let MATLAB do it for me. As you should see, you posed o...

6 days ago | 1

| accepted

Answered
i which library can i find those two functions (h-plane and e-plane) ?
There is NO such library, because those are not legal function names in MATLAB. A dash is not legal in a name, in a function OR ...

6 days ago | 0

Answered
How to neatly or properly display the answers for simultaneous equations?
You may want to learn how to use the symbolic toolbox, which can display answers in a form you may want. A = [2 3 5; 3 4 7; 1 1...

6 days ago | 0

| accepted

Solved


Divisible by 2
This is the first problem in a set of "divisible by x" problems. You will be provided a number as a string and the function you ...

9 days ago

Answered
First order derivative using Curve Fitter (smoothing spline fit)
For example, we might try using the same fit, on some data where I know the answer. x = rand(100,1)*2*pi; y = sin(x) + randn(s...

10 days ago | 0

Answered
csv to .mat file
help csvread help save Perhaps you need to do the Onramp MATLAB tutorial?

11 days ago | 1

Answered
Optimize function wich only admits scalar input
FIRST, NEVER return a variable that has the same name as your function. That is a dangerously, recursively incestuous operation ...

11 days ago | 0

Answered
How to tell solver that symbols are matrices
A = sym('a',[2,2]) As you can see, A is a 2x2 matrix. B = rand(2,2); X = rand(2,2); Asol = solve(A*X == B,A) So now, for ...

11 days ago | 0

Answered
How to simplify this symbolic equation - nominator and denominator manipulation
I never did understand why people worry about making a symbolic tool give a result in a mathematically identical form, that happ...

12 days ago | 0

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Answered
Estimate area inside point cloud
As long as the curve is a sequence of points defining the perimeter and they are distinct, you can just compute the area using a...

12 days ago | 1

Answered
Graphing a polyfit function
DON'T USE A HIGH ORDER POLYNOMIAL! DON'T USE A HIGH ORDER POLYNOMIAL! DON'T USE A HIGH ORDER POLYNOMIAL! Do I need to say it ...

13 days ago | 0

Answered
natural cubic spline interpolation matlab
PLEASE DO NOT SEND ME E-MAIL ASKING FOR HELP. I ask people not to do this. (Note that for those people who might decide to do so...

13 days ago | 0

Answered
How can I show only the data from variable?
Use semi-colons at the end of those lines where you do not want to see all the crapola dumped to the command window.

16 days ago | 0

Answered
New Variables & Name in loop
Don't do it. https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval...

17 days ago | 1

Answered
How to select last digit of numbers and put it into a matrix?
Well, since you did write a fair amount of code, homework or not is irrelevant. There are some issues with your code however. ...

17 days ago | 0

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Answered
Real solutions to polynomials
When you use solve, remember that first of all, it will be impossible to find algebraic solutions to a general polynomial of deg...

19 days ago | 0

Answered
Why in a function an output argument isn't saved to workspace?
Suppose you use ANY MATLAB function? How does it work? For example... x = 1:5; Suppose you want to compute the mean of that ve...

19 days ago | 0

| accepted

Answered
Hilbert Matrix in least squares polynomial regression
Is A really a hilbert matrix? LOOK CAREFULLY AT WHAT YOU WRITE!!!!!!!!! In fact, A is not even a valid 3x3 matrix. If you fail ...

20 days ago | 1

Answered
Find a value in a matrix
help max Look at the SECOND argument returned from max.

22 days ago | 0

Answered
How to find solution using VPASOLVE
You have 2 variables, with 4 equations. vpasolve is NOT a tool that attmepts to solve a problem APPROXIMATELY. You cannot use vp...

22 days ago | 0

Answered
how can I solve this problem..
Um, what do you expect? syms theta0 x=90; g=9.81; v0=30; y0=1.8; y=1; th = -y+tan(theta0)*x-g*x^2/(2*v0^2*cos(theta0)^2)+y0; ...

23 days ago | 0

Answered
How to find the row and column for a value within a matrix [c] nearest or equal to 700.
Easy. And there would be many ways to do it. c = rand(5,5)*1000 [~,ind] = min(abs(c(:) - 700)) [rowind,colind] = ind2sub(size...

23 days ago | 0

| accepted

Answered
function for addition 2^16 modulo
Your numbers are in BINARY form, and you want to add modulo 2^16. The simplest solution is to convert to a decimal integer. I'l...

24 days ago | 0

Answered
Numerically solve differential equation
This is just a parabolic PDE, assuming that Bi is a KNOWN constant. You just say it is constant. But you should be able to use ...

26 days ago | 0

Answered
3D best fit curve from x,y and z data points
You may think it is easy, if only you can find someone who has the magic touch. Sorry, but not so easy. If the curve is presum...

27 days ago | 1

Answered
HOW TO GET THE VALUES OF CONSTANTS
Please don't YELL! Next, NEVER define pi. pi already exists, and I hate to tell you, it ain't 3.14. That only happens in certai...

27 days ago | 0

Answered
Code help on Euler's method
What you need to understand is that Euler is a poor method to use. Easy to write, easy to understand. But is it good? NO. And th...

29 days ago | 2

| accepted

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