Question

I’m trying to find some way to substract a size 3 vector from each column of a 3*(a big number) matrix in Matlab. Of course I could use a loop, but I’m trying to find some more efficient solution, a bit like numpy broadcasting. Oh, and I can’t use repmat because I just don’t have enough memory to use it (as it creates yet another 3*(a big number) matrix)…

Is this possible?

Answer 1

Loops aren’t bad in MATLAB anymore thanks to compiler optimizations like just-in-time acceleration (JITA). etc. Most of the time, I’ve noticed that a solution with loops in current MATLAB versions is much faster than complicated (albeit, cool :D) one-liners.

bsxfun might do the trick but in my experience, it tends to have memory issues as well but less so than repmat.

So the syntax would be:

AA = bsxfun(@minus,A,b) where b is the vector and A is your big matrix

But I urge you to profile the loopy version and then decide! Most probably, due to memory constraints, you might not have a choice 🙂