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MathGroup Archive 2007

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Re: Options for a very large computation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77853] Re: Options for a very large computation
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Mon, 18 Jun 2007 07:01:28 -0400 (EDT)

On 6/17/07 at 6:04 AM, rdobrow at carleton.edu (Bob D) wrote:

>I'm solving a 24-by-24 linear system symbolically. After getting
>what I want using NullSpace, I get a very complicated expression in
>4 variables. When I try to Simplify the expression (before viewing)
>my system dies. Either I run out of memory, or, when I add
>TimeConstraints -> Infinity to the Simplify function, it takes
>"forever" (nothing after 8 hours).

>Two questions: (1) Any suggestions for how I can get more processing
>power, memory to do the calculations.

I suppose this can be accomplished in the same manner as anyone
else would, i.e., buy a faster machine, more memory etc.
Possibly, your code can be improved. But since you didn't post
any code, it isn't possible for me to offer meaningful
suggestions along these lines.

>(2) I have access to more power, but the programs need to be written
>in C++. Is there a way to convert the Mathematica code and the
>Simplify command, in particular,  to C++ and run it offline?

Take a look at the built in function CForm which converts a
Mathematica expression to C syntax. But while I've no doubt
CForm performs as designed I haven't used it and I strongly
suspect it will not be all that helpful to you. I don't believe
CForm will output C compatible code for specialized built in
functions such as Simplify.

I also strongly suspect even if Mathematica did output C code
for built in functions, it would not solve your problem to move
this to C or C++. The amount of computation needed to
symbolically solve a 24 x 24 system and find a simplified
solution is quite simply enormous.
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