Performance using temporary boolean filter

In a situation where I need to use a logical filter (simply a vector of logical) 3 times in succession, am I likely to get a performance improvement by creating a temporary variable to hold the filter and then referring to that where necessary as opposed to just repeating the filter expression explicitly? e.g. I could define say: filter=(floor(x)==y); then do something to A(filter), B(filter) and C(filter) or I could do something to A(floor(x)==y), B(floor(x)==y) and C(floor(x)==y)

Answer 1

[Jan]

A(floor(x)==y) creates the temporary array floor(x)==y explicitly. Therefore doing this three times needs more resources than making the comparison once only. Therefore A(filter) etc. is faster.

Answer 2

[Ryan Livingston]

The performance depends on many things. But it is likely that assigning filter will decrease the number of operations needed to be performed. Namely,

 floor(x)==y

will only be calculated once.

Try both examples and run your code through the profiler to see how it affects things:

http://www.mathworks.com/help/matlab/matlab_prog/profiling-for-improving-performance.html#f9-17117