Question

I am experiencing some very odd timing behavior from a function I wrote. If I wrap my function inside another empty container function, it gets a 3x speedup.

>> tic; foo(args); toc

time elapsed: ~140 seconds

>>tic; bar(args); toc

time elapsed: ~35 seconds

Here’s the kicker – the definition of bar():

define bar(args)

foo(args)

end

Is there some sort of optimization that gets triggered in MATLAB for nested function calls? Should I be adding a dummy function to every function that I write?

Answer 1

The JIT accelerator does not operate on command line expressions as far as I know. Thus, when you run “tic; foo(args); toc” foo’s code runs entirely in the MATLAB interpreter. However, when you run “tic; bar(args); toc”, bar is evaluated in the interpreter and the JIT accelerator takes a shot at compiling the call to foo() to native code.

I’m really waving my hands over the details, but that’s the gist of it. Details for MATLAB’s JIT capabilities are hard to come by; most of what I’ve found is on Loren’s blog at The MathWorks. The closest authoritative statement I can find about the command line being interpreter-only is here:
http://blogs.mathworks.com/loren/2006/05/10/memory-management-for-functions-and-variables/#comment-207