Concatenate large matrices a bottleneck in function

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.

[Sylvain]

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]

Hello -

Thanks for your comment.

I won't post my code because, yes, that is exactly what I am doing.

Answer 1

[Subhadeep Koley]

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);

[Walter Roberson]

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