       Efficient Replacement Rules to Matrix?

• To: mathgroup at smc.vnet.net
• Subject: [mg21743] Efficient Replacement Rules to Matrix?
• From: Roger Jones <rmj at leland.stanford.edu>
• Date: Wed, 26 Jan 2000 03:45:42 -0500 (EST)
• Organization: Stanford Univ
• Sender: owner-wri-mathgroup at wolfram.com

```What is the most efficient (in terms of time) method to transform a set
of replacement rules to a matrix.  For example, I have:

matrix = ZeroMatrix;
repmat = {{1, 1} -> 4., {5, 5} -> 3,{4, 4} -> 10,{2, 2} -> 2 + I 6, {3,
3} -> 40.};

and I transfor to a matrix thus:

matrix = ReplacePart[matrix, Sequence @@ #]) & /@ (
{Last[#], #[]} & /@ matrix);

But for large matrices this is quite slow!  Is there a more efficient
method?

I then will form a matrix product with this sparse matrix:
result= matrix.avector and this is indeed my goal.

I would appreciate any ideas on this matter.
Many thanks!

-Roger Jones

PS This comes to light in the context of using the new Mathematica
function "SparseLinearSolve"

```

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