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MathGroup Archive 1997

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Beware of Simplify[] bottlenecks in v 3.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg8925] Beware of Simplify[] bottlenecks in v 3.0
  • From: carlos at mars.Colorado.EDU (Carlos A. Felippa)
  • Date: Sat, 4 Oct 1997 22:08:04 -0400
  • Organization: University of Colorado, Boulder
  • Sender: owner-wri-mathgroup at wolfram.com

After installing v 3.0 on my Max 8500/120 I have done some side 
by side timing tests with old Notebooks comparing the speed of
Mma 2.2 vs 3.0.  Generally v. 3.0 is 10% to 60% slower in most cases,
but ocassionally I found it to be an order of magnitude slower.  
I traced the difference to the frequent use of the Simplify function.  
This used to be a bottleneck in 2.2, and can be even more so in 3.0.  

The following code fragment, extracted from an old Notebook, 
illustrates the dramatic speed difference:

fp=(a*(2*a + a*Cos[phiQ])*(2*a*Cos[phiQ]*(1 - Cos[theta]) +
 a*(1 - Cos[phiQ]*Cos[Pi/8]*Cos[theta] - Sin[phiQ]*Sin[Pi/8])))/
 (2*2^(1/2)*(5*a^2 - (2*a + a*Cos[phiQ])*(2*a + a*Cos[Pi/8])*Cos[theta] + 
 a*(2*a*(Cos[phiQ] + Cos[Pi/8]) - a*Sin[phiQ]*Sin[Pi/8]))^(3/2));
Print[Timing[fp=Simplify[fp]]];

Mma 2.2:  15.75 Seconds
Mma 3.0: 140.517 Seconds - same result

I tried to limit the operation to 15 seconds to see if 3.0 can return the 
same answer quicker:

Print[Timing[fp=Simplify[fp,TimeConstraint->15]]];

but the option is ignored:

Mma 3.0: 142.417 Seconds 

The purpose of this post is to warn users converting to 3.0 about
such bottlenecks, and that they are uncontrollable until the
TimeConstraint option works.




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