bsxfun

Just found this awesome function in Matlab called bsxfun. It is rather helpful, and fast too as illustrated below. Usage can be found at Matlab documentation (ofcourse!) or an example as below. It is called in a way a little similar to the late (deprecated) blkproc (or now, blockproc) function with an argument as a function. The “@fun” part.

The example here basically computes the difference, B is subtracted from each row of A.

>> A = rand(1000,3);
>> B = rand(1,3);
>> tic; C1 = bsxfun(@minus,A,B); toc;
Elapsed time is 0.003523 seconds.
>> tic; C2 = A - ones(1000,1)*B; toc;
Elapsed time is 0.090703 seconds.

Note that it performs the subtraction on the columns, (length 3). In case you specify B as B = rand(1000,1) then it will perform the subtraction on the rows (length 1000).

Another way to achieve the same operation, without using a loop, would be using repmat, but it is the slowest of them all. Ofcourse, you should NOT even think of using a loop for such a thing in Matlab!

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