Re: Parallelize vs Compile

*To*: mathgroup at smc.vnet.net*Subject*: [mg119380] Re: Parallelize vs Compile*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Wed, 1 Jun 2011 04:33:48 -0400 (EDT)

On 5/31/11 at 7:46 AM, ngoble at iwu.edu (Nicholas Goble) wrote: >My code seems to run much more quickly when I only use Parallelize[] >as compared to any combination of Parallelize and Compile. Even >when I compile into C using CompilationTarget->"C" and with >Parallelization->True. >I thought that compiling would always make a program in Mathematica >run faster. Why does it slow down? Is Parallelize always the most >efficient? No, compiling will not make any program faster in Mathematica and Parallelize will not always be the most efficient. Compile seems to produce the most improvement for proceedural code, i.e. code using something like a For loop. There are numerous examples where Compile cannot compile the code and the code runs uncompliled. My experience with Mathematica has been whenever Complile does improve performance, most if not all of that performance gain can be achieve by using functional programming in an optimal manner. Parallelize isn't always the most efficient since Mathematica does not know how to parallelize some built-in functions. And in these cases, there is overhead when attempting to use Parallelize. Mathematica tries to parallelize the problem, determines it cannot then runs the problem on a single core normally. Both Compile and Parallelize can significantly improve performance of some code. But neither can be guaranteed to do so. Neither is a silver bullet. There really is no substitute for understanding the problem you are trying to solve, how your code runs and what resources Mathematica already has built-in that are relevant to the problem you are trying to solve.