Strategy for overly long computations?
- To: mathgroup at smc.vnet.net
- Subject: [mg35327] Strategy for overly long computations?
- From: "Peter S. Shenkin" <shenkin at mindspring.com>
- Date: Mon, 8 Jul 2002 03:19:24 -0400 (EDT)
- Organization: MindSpring Enterprises
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
I'm trying to solve a set of 5 eqns in 5 unknowns, three of which
are quadratic and two of which are linear. I'm only interested
in three of the unknowns, so first I eliminate the other two.
So far, Mathematica 4.0 on an UltraSPARC has been grinding away for
over 24 hours on this system at 96% of the CPU. There are no
errmsgs.
Does anyone out there have any insight into any of:
1. Whether this system is so tough it'll take "forever" to get
through all the possibilities;
2. Whether there's some way of reorganizing the calculation so
that Mathematica can work faster;
3. Whether I'm encountering some sort of bug or malfunction;
4. Whether I'm doing something really stupid.
Thanks. The system is shown here; I'm running in background,
redirecting stdin from a file with contents shown here. The
calculation through the first Save is nearly immediate; almost
all the time so far is taken up in the Reduce step.
For clarity, let me say that I'm running the job as:
math < intersect >& intersect.log &
-------------------
cn1 = ( x - x1 )^2 + ( y - y1 )^2 + ( z - z1 )^2 == r1^2
cn2 = ( x - x2 )^2 + ( y - y2 )^2 + ( z - z2 )^2 == r2^2
lgrx = ( x - xv ) + lm1 * ( x - x1 ) + lm2 * ( x - x2 ) == 0
lgry = ( y - yv ) + lm1 * ( y - y1 ) + lm2 * ( y - y2 ) == 0
lgrz = ( z - zv ) + lm1 * ( z - z1 ) + lm2 * ( z - z2 ) == 0
lgrxyz = { lgrx, lgry, lgrz }
elim = Eliminate[ lgrxyz, {lm1,lm2} ]
eqns = { cn1, cn2, elim }
Save[ "intersect.out", cn1, cn2, lgrx, lgry, lgrz, lgrzyx, elim, eqns ]
redn = Reduce[ eqns, {x,y,z} ]
Save[ "intersect.out", redn ]
soln = Solve[ eqns, {x,y,z} ]
Save[ "intersect.out", soln ]
-------------------
-P.
--
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Peter S. Shenkin = Dull boy
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