"Matthias Troyer" <troyer@itp.phys.ethz.ch> wrote in message news:E934060C-FDD6-40AC-A575-1B4907DBDF6D@itp.phys.ethz.ch...
On Aug 21, 2006, at 8:38 AM, Andy Little wrote:
"Matthias Troyer" <troyer@itp.phys.ethz.ch> wrote
<...>
The above creates a lot of temporaries of course.
Why? Using expression templates there will be absolutely no temporaries.
In my experiments with E.T, I found that it only became advantageous when use with (say) a vector of more than 4 elements. Before that it seemed to create more temporaries than eager evaluation. I seem to remember someone else backing this up somewhere too.
That's strange since there should be no temporaries at all. The only thing to keep in mind is that in short loops over only 3 or 4 elements the time often gets dominated by the control structure of the loop and the inability to fill pipelines efficiently. Using small fixed-size data structures, such as the TinyVector in Blitz++ completely remedies that problem, and Dave's matrix library will take care of this as well. You still have not shown any reason why a special purpose matrix and vector library in Quan would be needed or useful.
I suppose that at the end of the day, I am just interested in writing a very basic linear algebra library for Quan, especially to try to understand quaternions. regards Andy Little