How to use tril function on only specific columns in a large matrix?
1 view (last 30 days)
Show older comments
Zuha Yousuf
on 19 Mar 2020
Commented: Zuha Yousuf
on 19 Mar 2020
So I have a very large matrix (31413 rows, 950 columns). I want to use the tril function on columns 2 till 10, and then from 12 to 20, and then from 22 to 30, and so on until the end of columns.
I need something like this
[col1 col2...col10 col11 col12...col20 col21 col22...col30 and so on]
where the columns in between have tril function used on them.
Is there any way I can do this??
0 Comments
Accepted Answer
Sriram Tadavarty
on 19 Mar 2020
Edited: Sriram Tadavarty
on 19 Mar 2020
Hi Zuha,
You can use a for loop as below and it does what is required:
m = rand(31413,950);
for i = 2:10:size(m,2)
m(:,i:i+8) = tril(m(:,i:i+8));
end
Hope this helps.
Regards,
Sriram
More Answers (1)
David Goodmanson
on 19 Mar 2020
Hi Zuha,
here's another, more vectorized version
m = rand(31413,950);
[r c] = size(m);
[jj ii] = meshgrid(1:c,1:8); % ii row jj col
ind = ii<mod(jj-1,10);
m18 = m(1:8,:);
m18(ind) = 0;
m(1:8,:) = m18;
It's faster than the for loop version, which is not a big deal since Sriram's code only takes 0.2 sec, and that code is more self-explanatory.
See Also
Categories
Find more on Linear Algebra 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!