Re: [MacPerl] MacPerl speed vs MachTen FORTRAN

["Paul J. Schinder" <schinder@pobox.com>]

At 8:07 PM -0600 11/18/98, William H. Asquith wrote:

} I'm building 20000 line arrays for some statistical research.  I have
} working algorithms in FORTRAN, which I'm running under MachTen 4.1.  Speed
} is reasonable for each build of the array.  I'm excited about MacPerl and
} decided yesterday to port the FORTRAN to MacPerl.  Now the array builds much
} slower.  I've changed a DO (ie FOR) loop to a WHILE (supposed to be faster
} from Programming Perl) and am PUSHing each element onto the array.  This
} speed things up a little bit, I think.

You might be able to pick up some speed by preallocating the array.
(Something like $#$betainverseref = 20000 might do it, but I'm not sure
that syntax works properly with a reference.  I suppose it should.)

}
} Basically, my question to all of you is: Should I expect MacPerl to run
} slower than FORTRAN on MachTen?  Seems amazing to me since I'd expect
} working in the native MacOS to be faster than an emulated Unix.

I wouldn't expect that at all.  First, I'm not that familiar with MachTen
but my understanding is that it's not an emulator at all, but real BSD Unix
running in a MacOS box.  Second, Fortran is still the premier language for
numerical work for good reasons.  Like all compiled languages I've ever
used, a Fortran array is a "real" array (contiguous values are contiguous
in memory). Fortran allocates the memory at startup.  Perl arrays are not
arrays in sense that C or Fortran arrays are; each Perl is a C structure
(called an SV if memory serves; the details can be found at Gisle Aas'
Perlguts Illustrated: <http://home.sol.no/~aas/perl/guts/>), and arrays are
collections of SV's.  There's probably some optimization going on, but as
written each time through your loop Perl has to allocate memory (larger
than 8 bytes) and put a value in the right slot.

There's a Perl extension available from CPAN named PDL which is an attempt
to teach Perl how to deal with "real" arrays.  Be warned that of the three
flavors of Unix I use regularly I've only gotten PDL to work on one of them
(LinuxPPC), and only over the last weekend when I discovered that it would
test clean if I turned egcs' optimizer off.  It will not work under MacOS
at all, I'd guess. (In any event to even attempt to get it to work you'd
need both a C and Fortran compiler that will work together.)  It may work
under MachTen.  It may or may not speed things up for you; I have very
little experience actually using it.

Personally I do some of my numerical work in Perl, but not when I'm worried
about speed.  If I was worried about speed, I'd use C or Fortran; Perl can
certainly be no faster than a pre-compiled language, and is probably going
to be slower.  I use Perl mainly for postprocessing and graphics (using
PGPLOT).

}
} Below is the salient code frag.
}    while( $i <= ($nF-1) ) {
} #      print STDOUT "  BETAINVER i = $i\n";
}       $x = $i*$dF;
}       $F = &BETAI($a,$b,$x);
}       if($F == -9999) {
}          $flag = -9999;
}          $betainverseref = "";
}          return $betainverseref, $flag;
}       }
}       push(@$betainverseref, $F);
}       $i++;
}    }
}    return $betainverseref, $flag;
}
} Thanks,
} -wha
}

-----
Paul J. Schinder
schinder@pobox.com

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