Re: Listable parallel basic LibraryLink dll

*To*: mathgroup at smc.vnet.net*Subject*: [mg122498] Re: Listable parallel basic LibraryLink dll*From*: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>*Date*: Sun, 30 Oct 2011 04:22:15 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201110251018.GAA05905@smc.vnet.net>

Hi, I think this is currently not possible. But one can of course investigate a bit how Mathematica does it. In the following I talk exclusively about compiled functions having CompilationTarget->"C" and my system is Linux which may behave very differently. 1. When you use compile and build two versions of your function, one that's normal and one that's parallelized and listable, and you used then ExportString[func,"C"] on these you'll see, that the c-code is the same. Therefore, it seems not to be possible to export this behaviour into c-code. 2. On the other hand, if you have a compiled function, you could use InputForm on the listable function to see how it looks inside. For a simple dummy function this looks on my Linux box like this here: CompiledFunction[{8, 8., 5852}, {_Real}, {{3, 0, 0}, {3, 0, 1}}, {{1, {2, 0, 0}}}, {0, 1, 5, 0, 0}, {{40, 1, 3, 0, 0, 3, 0, 1}, {40, 56, 3, 0, 0, 3, 0, 2}, {10, 0, 3}, {13, 3, 0, 3}, {40, 58, 3, 0, 3, 3, 0, 4}, {19, 4, 3}, {13, 1, 2, 3, 1}, {1}}, Function[{x}, Sin[x] + x^2 - 1/(1 + x), Listable], Evaluate, LibraryFunction["/home/patrick/.Mathematica/ApplicationData/CCompilerDriver /BuildFolder/warp-4499/compiledFunction1.so", "compiledFunction1", {{Real, 0, "Constant"}}, Real]] "compiledFunction1.so" is the parallel version, so lets keep this library and load it later by hand. I moved it to another location (when you close a kernel, all created library-code is deleted) and loaded it on a fresh kernel with f = LibraryFunctionLoad["compiledFunction1", "compiledFunction1", {{Real, 0, "Constant"}}, Real] what I got was a listable, parallelized function CompiledFunction[{x}, Sin[x] + x^2 - 1/(1 + x), -CompiledCode -] which suggests that (1) the c-library code is aware of the general analytic expression. Therefore, you could call f[t^2] and get the correct result. (2) The listable attribute and the parallelization go indeed into to library. 3. To check what happens when you really call the compiled function I used "ltrace" (if you're with Bill Gates, you may not know this) and listed all functions of all (sytem-)libraries which were used during the call. Comparing the results for a parallel and a serial call brought up this line to my attention, which appeared in the parallel call but not in the serial: 8 pthread_cond_wait It says that this function was called 8 times and happy enough I have exactly 8 cores which were used in the parallel call. For all these reasons I think we can assume the following. The parallelization and the listable attribute, as well as the analytic expression go into the c-library if you use Compile. It seems not possible to get this behaviour by exporting c-code and I did'nt find documentation which explains how to write a library-function which is listable and parallelized. BUT, you can of course write your own parallel function with OpenMP, TBB, or whatever you prefer and call it. Cheers Patrick On Tue, 2011-10-25 at 06:18 -0400, Rui wrote: > I've just started with LibraryLink. I'm actually mostly interested in getting the basics so I can start leaning while I use it. > I could get some basic C++ code of mine to link well with Mathematica. > > Do you know how to make it behave like a CompiledFunction with the Listable attribute and parallelization set to True? > > Thanks >

**References**:**Listable parallel basic LibraryLink dll***From:*Rui <rui.rojo@gmail.com>

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