Help on a Function
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Greetings!
I would like your help on a function I'd like to make on Matlab.
I want to make a function called R,
[Roots] = R(X,Y,eps) and this function will be returning a table with 2 columns showing the X and Y of the points where abs(Y)<eps
Thank you in advance.
4 Comments
dpb
on 30 Nov 2019
I suggest reading the Getting Started tutorial sections in the online documentation...it outlines basic syntax and operations that will get you started. There are lots of examples of writing simple functions with the doc for function
Logical addressing is the trick for such questions as this...see what
eps=0.5;
x=rand(10,1);
x(x<eps)
does.
Answers (3)
Image Analyst
on 1 Dec 2019
Try this (untested)
% This function will be returning a table with 2 columns showing the X and Y of the points where abs(Y)<eps
function [Roots] = R(X,Y,eps)
Roots = []; % Initialize to no values.
indexes = abs(Y) < eps;
if isempty(indexes)
% No Y satisfies the criteria.
return;
end
xSmall = reshape(X(indexes), [], 1); % Extract indexes and make sure they're in a column vector.
ySmall = reshape(Y(indexes), [], 1); % Extract indexes and make sure they're in a column vector.
Roots = table(xSmall, ySmall);
end
5 Comments
Image Analyst
on 1 Dec 2019
Of course. dpb was merely showing what would happen if I didn't use reshape to turn the data into a column vector before passing in to the table() function. It was not a separate answer in itself, and I did use reshape() so I did it correctly.
Dhmhgr
on 1 Dec 2019
1 Comment
Image Analyst
on 1 Dec 2019
I didn't notice at first that we were using eps. That is probably a bad thing to use (unless it's a trick question) because no value of Y can be less than eps unless it's pure zero.
Try this (with a variable named minValue):
X = rand(1, 100);
Y = rand(1, 100);
minValue = 0.1;
Roots = R(X,Y,minValue)
% This function will be returning a table with 2 columns showing the X and Y of the points where abs(Y)<eps
function [Roots] = R(X,Y,minValue)
Roots = []; % Initialize to no values.
indexes = abs(Y) < minValue;
if isempty(indexes)
% No Y satisfies the criteria.
return;
end
xSmall = reshape(X(indexes), [], 1); % Extract indexes and make sure they're in a column vector.
ySmall = reshape(Y(indexes), [], 1); % Extract indexes and make sure they're in a column vector.
Roots = table(xSmall, ySmall);
end
You'll see
Roots =
11×2 table
xSmall ySmall
_________________ ___________________
0.970592781760616 0.0838213779969326
0.792207329559554 0.0781755287531837
0.849129305868777 0.00463422413406744
0.743132468124916 0.0844358455109103
0.489764395788231 0.0759666916908419
0.679702676853675 0.0496544303257421
0.890903252535798 0.0964545251683886
0.257508254123736 0.0597795429471558
0.243524968724989 0.0154034376515551
0.929263623187228 0.0430238016578078
0.567821640725221 0.0811257688657853
Dhmhgr
on 2 Dec 2019
Edited: Walter Roberson
on 2 Dec 2019
2 Comments
Image Analyst
on 2 Dec 2019
eps, which remember I said must be renamed, can be anything. Whatever you want. Whatever you use, R will find the points, if any exists, or null if they don't.
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