How to do Subtraction on sets?
1 view (last 30 days)
Show older comments
I have a continuous set (A=[0 , 2pi]) and want to subtract the following sets from it:
B= [0, pi/2];
C=[pi/4, pi];
D=[3pi/2, 7pi/4];
...
In general, I could just build the union of "B, C, ..." and then do the subtraction BUT I have to do this process a lot of times. In other words, the whole process is in a "for loop" and each time some sets need to be subtracted from A (each time the number of sets and their length is not necessarily might change). The initial interval (A) is the same for all the iterations (after each iteration I would get an interval corresponding to that iteration: Answer(i) = A - B(i) - C(i) -...).
I found a function in MATLAB called "setdiff" but it seems to only work on discrete intervals or images (I mean a 2D matrix)!
Is there a similar function for continuous intervals/sets?
Any help would be appreciated,
1 Comment
Image Analyst
on 6 Jul 2014
What's a continuous set? There is no continuous set of numbers in computers. If A is an array, then A has a certain, fixed and finite number of elements with certain definite values, so A must be discrete/digitized, not continuous.
Accepted Answer
Image Analyst
on 6 Jul 2014
Try this:
A = 0:360;
B = 0 : 60;
C = 45 : 60;
D = 270 : 360;
foundIndexesB = find(ismember(B, A))
foundIndexesC = find(ismember(C, A))
foundIndexesD = find(ismember(D, A))
allFoundIndexes = [foundIndexesB, foundIndexesC, foundIndexesD]
% Get rid of those numbers from A
A(allFoundIndexes) = [];
Note, it only works for integers. Why? See the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
2 Comments
More Answers (1)
Roger Stafford
on 6 Jul 2014
You might consult these sites:
http://www.mathworks.com/matlabcentral/fileexchange/31753-range-intersection
http://www.mathworks.com/matlabcentral/fileexchange/24254-interval-merging
See Also
Categories
Find more on Matrices and Arrays in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!