       Re: Massive memory issues when using Det

• To: mathgroup at smc.vnet.net
• Subject: [mg127324] Re: Massive memory issues when using Det
• From: Jonathan Frazer <J.Frazer at sussex.ac.uk>
• Date: Tue, 17 Jul 2012 01:30:05 -0400 (EDT)
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• References: <20120711061823.1AE5D684B@smc.vnet.net>

Also, I was trying to work out how to use the parallel computing
options but when I tried Parallelize[Det[g]] Mathematica said no. How
do I know if something is parallelizable or not?

Sorry for the stupid questions. This is all rather new to me.

Thank,

Jonny

On 16 Jul 2012, at 12:04,  wrote:

> Hi
>
> I'm having a lot of trouble calculating the determinant of even a 3x3 matrix. The expressions are large but all aspects of the program are handling them fine except Det.
>
> Is Det trying to simplify the expressions by any chance? Is there anything I can try? Below is an example of how I construct the matrix but this example is much simpler. The difference is S\theta\alpha and C\theta\alpha are bigger expressions in the real thing. As far as I can tell the code is logically fine. It works for smaller dimension problems with no trouble at all.
>
> Right now I have been trying to evaluate Det for about 3 hours and its taking up almost 12 GB of memory.
>
>
> Jonny
>
> On 11 Jul 2012, at 18:39,  wrote:
>
>> d = 2;
>> èá = Table[Symbol["è" <> ToString[i]], {i, d - 1}];
>> Sèá = Sin[èá];
>> Cèá = Cos[èá];
>> sè = r Prepend[Table[Product[Sèá[[á]], {á, i}], {i, d - 1}], 1]*Append[Cèá, 1];
>> ë = Outer[D[#1, #2] &, sè, èá];
>> g = Table[Sum[ë[[ã, á]] ë[[ã, â]], {ã, d}], {á, d - 1}, {â, d - 1}];
>> vol = Sqrt[Det[g]]
>>
>



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