OPR-computation-related linear algebra problem

[RyanCahoon]

Hi Ether,

Originally Posted by Ether

I compiled it with Borland C++ 5.5 and ran it [...] It took 80 seconds

That's quite a large difference in runtime. I compiled mine with Visual Studio 2010. I had wondered if VS was able to do any vectorized optimizations, but I don't see evidence of that in the Disassembly.

Originally Posted by Ether

If your code took only 3 seconds to run on your machine, but 80 on mine, I'm wondering what the Rice algorithm would do on your machine.

If I'm reading the pseudocode you posted correctly, I think I'm using the same algorithm (I got mine from the formulae on Wikipedia), the only difference I could find is I didn't handle the case of roundoff errors leading to slightly negative sums for the diagonal elements and I do some of the sums in reverse order, but unless there's some drastically bad cache effects I don't see that impacting the runtime.

Makes me wonder what you may have done better in your coding of the algorithm.

EDIT: Changing the order of the summations got me down to 2.68 and changing to in-place computation like your code got me to 2.58. Beyond that, any improvements would seem to be in the way the Pascal compiler is generating code.

Best,