Christian, 1. in my previous post i used exactly that same constructor you are talking about as you can see from the code i posted
2. i am not doing any math in this illustrative example, i am just modifying a toy matrix and showing that this modification didn't propagate back to R. Which means i am operating on a different chunk of memory, i.e. i made a copy somewhere. In real life I need to do a some fairly involved manipulations on several matrices each couple of gigs big, so it'd be nice not to copy. I have armadillo code that does the job, but i wanted to call it from R without copying the matrices. In pure R this stuff takes very long time. 3. i am not 100% sure but this toy test that i did seem to indicate to me that a copy is done regardless by NumericalMatrix. I need to see the code for NumericMatrix to be absolutely sure, but i cannot explain things otherwise On Wed, Nov 2, 2011 at 12:31 AM, Christian Gunning <x...@unm.edu> wrote: > > 1: For the NumericMatrix->arma, you can use an advanced constructor > to get the behavior that you desire. > http://arma.sourceforge.net/docs.html#Mat -- you'll want copy_aux_mem > = false. > > 2: Are you actually doing matrix math? If you're just doing simple > element-by-element arithmetic, you might get just as good performance > with a simple loop or iterator. You might try this first to > understand the R/C++ process, and *then* move to using Armadillo :) > > 3: For completeness, note that "Rcpp::NumericMatrix r_m(clone(mem));" > *forces* a copy, thus restoring R's "no side-effects" semantics. > > -Christian > > > > -- > A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal – Panama! >
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