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Re: Mathematica 8: first impressions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113998] Re: Mathematica 8: first impressions
  • From: blamm64 <blamm64 at charter.net>
  • Date: Sat, 20 Nov 2010 06:13:12 -0500 (EST)
  • References: <ic34r0$5rv$1@smc.vnet.net>

First Impressions:

1)  Regarding NDSolve.  I submitted, on the same machine, an
identical, not-that-complicated, mutl-rigid-body dynamics set of
differential equations (only six unknowns) to Mathematica 8 and to
Mathematica 7.0.1: Timing - 7.0.1 = 1.482 seconds; 8.0 = 219.218
seconds (averaged over three submissions of identical model).  Even
though the system is 'purely' differential (not DAE), I forced
Mathematica to use IDA, since *my* experience has been it is superior
to other methods for handling stiff systems (maybe it defaults to
LSODA where SolveDelayed->True is used and the system is not DAE; I've
no idea).  Need I even write that's not good?  And I mean *identical*;
I simply ran the same notebook in 8.0 and then in 7.0.1., after
restarting OS.  Plotting of characteristics (constraint forces) had
time disparities even worse than the disparity in Timing to solve.
One such plot ran in 1. seconds in 7.0.1 and 529.562 seconds in 8.0.
Perhaps Mathematica 8.0 no longer implements the fantastic suite
authored by Hindmarsh, especially IDA???
NDSolve is promulgated by Wolfram as being the 'biggest' "super-
function" available in Mathematica and apparently pretty great strides
have been taken ... in the wrong direction, at least for this
particular case of mine.  I might mention the results of the
simulations were virtually identical, so NDSolve in Mathematica 8.0
did not uncover anything new.  I'll run some even more involved models
I've previously created and compare.

2) 64-bit has been around long enough to be pretty well received:  In
Mathematica 8.0 $MachinePrecision is still 15.9.... on my Intel,
Windows XP x64 machine (2x 4-core Intel Xeon X5570, nVidia Quadro FX
4800, 24 GB RAM) .  Yeah, sure, Wolfram a good while back implemented
Mathematica to use 64 bit addressable memory (which really helps since
it's such a RAM hog), but still not to have implemented using 64-bit
available 'precision' is very disappointing ... .  Yeah, Mathematica
uses double precision 32 bit to get 15.9... machine "precision", but
by now I think Mathematica, if installed on a 64-bit system, should
have $MachinePrecision of 31.8.... , or something close to that on a
64-bit system.

Yeah, sure, *Great* strides have been implemented and I'll never tap
into even a small fraction of what's available, I'm sure, but to not,
apparently, give good attention to *core* functionality is
disappointing.

I'm sure I'll find some really great features that are very useful and
powerful not found in versions previous to 8.0, I still consider
myself a beginner with Mathematica, but the above two points in my
opinion are valid complaints.

-Brian L.



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