How can I make indexing faster, that is, searching for a groups of numbers within a matrix?
1 view (last 30 days)
Show older comments
Hello!
I was wondering if there was anything faster than this:
X = ( Y1 < a & Y1 >= b & Y2 >= c & Y2 < d );
I run it in a loop a lot and it is by far taking up the most time. X is a group of numbers that meets 4 conditions. I am searching two large matrices, Y1 and Y2 for numbers that meets that condition. Anyone have an easier way?
I am on Matlab 2015a, 64bit, 120GB Ram, and blazing fast processors.
Thanks!
11 Comments
Accepted Answer
Walter Roberson
on 5 Jun 2015
In the special case that a relatively small fraction satisfies one of the conditions, and letting letting C1, C2, C3, C4 be the conditions ranked from least to most probable, such as C1 being "Y1 >= B", then you might try:
X( (((sparse(C1) & C2) & C3) & C4 )
for example
X( ((sparse(Y1 >= B) & (Y2 < d)) & (Y2 >= c)) & (Y1 < a) )
I don't promise it will be faster, but in theory it could be.
Note: this has more overhead than the way you used, so your occupancy needs to b less than... ummm, perhaps 1/4 maybe... before this gets speedup.
More Answers (0)
See Also
Categories
Find more on Matrix Indexing 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!