MATLAB Answers

Concatenate large matrices a bottleneck in function

3 views (last 30 days)
David McVea
David McVea on 4 Nov 2020
Commented: Walter Roberson on 4 Nov 2020
Hi,
I have a function that concatenates two matrices, size of 100000 X 90 for an outcome of 100000 X 180.
This is a significant bottleneck as the function has to repeat many times.
Pre-allocating the outcome does not seem to make any difference, and using cat() or [] also seems to make no difference.
Does anyone have suggestions on how to speed this up?
Thank you.

  2 Comments

Sylvain
Sylvain on 4 Nov 2020
can you post your code?
are you trying to do this ?
A=ones(100000,90);
B=2*ones(100000,90);
C = [A,B];
David McVea
David McVea on 4 Nov 2020
Hello -
Thanks for your comment.
I won't post my code because, yes, that is exactly what I am doing.

Sign in to comment.

Answers (1)

Subhadeep Koley
Subhadeep Koley on 4 Nov 2020
The horzcat() function is usually faster than cat() or [, ]. You may use it.
A = ones(100000,90);
B = 2*ones(100000,90);
result = horzcat(A, B);

  1 Comment

Walter Roberson
Walter Roberson on 4 Nov 2020
The timing tests I tried show horzcat(A,B) and [A,B] and cat(2,A,B) to be indistinguishable in timing -- the differences were below random variation

Sign in to comment.

Products


Release

R2018b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!