Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2001
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2001

[Date Index] [Thread Index] [Author Index]

Search the Archive

Solving linear equations with symbolic RHS

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30141] Solving linear equations with symbolic RHS
  • From: "Tony MacKenzie" <mackenzi at usq.edu.au>
  • Date: Tue, 31 Jul 2001 04:27:13 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Once again I would like to thank everyone who helped with my last post. This
question is more general and therefore probably much more difficult to
answer.

I am trying to solve linear equations of the form  A.x=b.  A is a completely
numeric matrix but b is a symbolic vector. I have tried Solve and
LUDecomposition but neither of these seem to work very well when b is a
symbolic vector.  What has worked the best for me is to invert the matrix A
(There is no problem with ill-conditioning) and to multiply by the symbolic
vector b.  However, what slows this process down is when I expand the
result.

Ainv=Inverse[N[A,16]];
soln=Ainv.N[b,16];
Expand[soln];  (This last steps slows down dramatically as the size of the
problem increases).

Each element of the symbolic solution vector may have a large number of
terms.

I realise this question I am posting is quite vague but if anyone has any
ideas it would be greatly appreciated.

Tony MacKenzie




  • Prev by Date: Fwd: Re: Re: Filename as Function Argument"
  • Next by Date: Re: Integrate[Sqrt[Tan[x]], {x, 0, 1}] -- approx ??
  • Previous by thread: SquareFreeQ vs. MoebiusMu
  • Next by thread: Lists and speed