On Dec 24, 2007 1:29 PM, Ondrej Certik <[EMAIL PROTECTED]> wrote: > Hi John, > > > When using g77 compiler instead of gfortran, I get a speed > > > up 4.8 times. > > > > The difference between g77 and gfortran with version 4.3 is now very > > small, plus gfortran is going to benefit from all the new > > vectorisation and optimisation work in gcc. It will not be long before > > it over takes for good. In addition you can use modern fortran 95/2003 > > code which makes life much easier! In in addition to all that it is > > very actively maintained and destined to be the default compiler on > > all linux systems as it is bundled with gcc. > > Yes, I also think gfortran is the way to go, since g77 is dead upstream. > But currently, the g77 still gives quite a lot faster code than gfortran, > but I hope it will change.
Yes, I just proved myself wrong (not a rare occurrence...), on my slow laptop: With gcc (4.3.0 20071223 (experimental)): real 0m3.272s user 0m3.120s sys 0m0.044s With gfortran (4.3.0 20071223 (experimental)): real 0m4.294s user 0m3.976s sys 0m0.020s With g77 (3.4.6): real 0m2.928s user 0m2.812s sys 0m0.044s If g77=1.0 then gcc=1.27 and gfortran=1.41 (far from 4.8 times though!!) This is in contrast to my recent experiments between gfortran and gcc, though that code used f95 stuff extensively so was never tested against g77. > So your suggestion is to prepare a clean fortran example, that, > when compiled with gfortran, runs a lot slower, than if compiled with g77? > Yep, I can do that. The most interesting will be to compile with g77 and gfortran with the options to spit out the generated assembler code, then we can see exactly where the difference is. I'll dig back in the gfortran mailing lists and see previous conclusions of the g77 vs gfortran debate (which occur often). You may just be exercising a particularly unoptimized part of gfortran. > So what is your personal opinion about fortran vs C for scientific computing? > >From the social point of view, I much prefer C, since a lot more people > know it, but as you say, the good fortran compilers are a lot better, than > the C compilers. So I don't know. Probably depends on the project and > a code I want to reuse. If you haven't guessed I'm pro fortran! My path was C++ -> Matlab -> Scipy (which I still use for prototyping and short calculations) -> fortran for big simulations. Of course, the wonderful f2py helps combining the last two steps! The turning point came when I discovered modern object orientated fortran features and particularly the array intrinsics/operations in fortran 95/2003. I realised that I could code my stuff in almost as few lines as Matlab and Scipy and also have the fastest execution (if using commercial compilers). My hope (slightly set back today) is that gfortran will mature into being as fast/faster than gcc/g77 for most code. In that case, with gcc on every linux system, then the social opposition should disappear. Though this still will not help against people who think f77 is fortran, ignoring the last 30 years of development. Anyway, I really must go home now... John _______________________________________________ Numpy-discussion mailing list [email protected] http://projects.scipy.org/mailman/listinfo/numpy-discussion
