double **

pdupre has asked for the wisdom of the Perl Monks concerning the following question:

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Re: double ** by samtregar (Abbot) on Jul 02, 2008 at 21:15 UTC
There isn't one. You've got a couple options that I know of. First, you could write pull the NVs out of your AVs and put them into a new double [][] that you New() and Safefree() on the spot. That will use lots of memory if your array is big. Alternately you could have your Perl code keep your data in packed C arrays to begin with, using something like Tie::CArray. Then you can write a little XS to put out the double** from that and pass it to your C code. -sam	[reply]
Re^2: double ** by pdupre (Acolyte) on Jul 03, 2008 at 15:55 UTC
Hello Sam, thank for your email. SO my conclusion is that it is going to be efficient to call a c routine with a AoA, I imagined that the machine representation was close between a AoA and a double [][]! It looks like that I am wrong. Will it it be a lot more efficient to pass several double [] ? Regards. Patrick Dupre The University of York	[reply]
Re^3: double ** by BrowserUk (Patriarch) on Jul 03, 2008 at 17:00 UTC
Just a thought, but maybe you could utilise PDLs piddles in your perl code and obtain the address of it for passing to your C code? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^4: double ** by pdupre (Acolyte) on Jul 03, 2008 at 19:35 UTC
Re^3: double ** by samtregar (Abbot) on Jul 03, 2008 at 16:50 UTC
Yup, AVs and C arrays are very different beasts. If the volume of data is the same I don't think you'll see a big difference between a double[][] and several double[]s but only you know the details well enough to judge. -sam	[reply]