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MathGroup Archive 2005

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Re: Any ideas about solving an underdetermined system?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58533] Re: [mg58514] Any ideas about solving an underdetermined system?
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Wed, 6 Jul 2005 03:11:17 -0400 (EDT)
  • References: <200507050852.EAA07178@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Jul 5, 2005, at 4:52 AM, Zhengji Li wrote:

> Dear Mathematica ers,
>
> Mathematica has a method of given the mininum-length solution.
>
> Let (x1, x2, ...) be a solution, I want that there are as many X-es  
> equal to 0.
>
> In other words, I want to solving a  underdetermined system in which
> many unknowns might be 0. And if I known which ones are 0, then the
> system may be simplified to a overdetermined one.
>
> Any ideas?

I'm not sure I understand your question.  I presume you mean you are  
obtaining solutions to an underdetermined linear problem by  
PseudoInverse.  If you set specific xi to 0 that's equivalent to  
removing those columns from your coefficient matrix.  So you could  
just use Part or Take to remove those columns, solve as usual then  
insert zeroes at the appropriate location in the solution.

Regards,

Ssezi


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