John D'Errico

Last seen: Today

Retired

5,742 2006 年以降の合計貢献数

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

約18時間前 | 1

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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 ...

3日前 | 0

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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...

3日前 | 1

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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 ...

4日前 | 0

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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...

4日前 | 0

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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 ...

6日前

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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...

7日前 | 0

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

8日前 | 1

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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 ...

8日前 | 0

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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 ...

8日前 | 0

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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...

9日前 | 0

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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...

9日前 | 1

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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 ...

10日前 | 0

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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...

10日前 | 0

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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.

13日前 | 0

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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...

14日前 | 1

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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. ...

14日前 | 0

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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...

16日前 | 0

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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...

16日前 | 0

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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 ...

17日前 | 1

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

19日前 | 0

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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...

20日前 | 0

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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; ...

20日前 | 0

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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...

20日前 | 0

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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...

21日前 | 0

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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 ...

23日前 | 0

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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...

24日前 | 1

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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...

24日前 | 0

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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...

26日前 | 2

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Can I change a 3-tensor into a matrix by indexing with a matrix?
A = randn(4,4,3) % Not very creative in making up numbers. So sue me. :) [~,I] = min(abs(A),[],3) What is I? For every combina...

26日前 | 1

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John D'Errico

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