Subj : Re: Faster matrix permutation algorithm?
To   : comp.lang.c,comp.programming
From : Michael Mair
Date : Sat Aug 13 2005 03:09 pm

Jack Middleton wrote:
> I'm lookin for a faster permutation algorithm for matrices. I know that 
> it can be done with multiplying a matrix with a permutation matrix. It 
> just seems a waste to iterate through all those zeroes. Is there an 
> algorithm for matrixes that is optimized just for permutations? The 
> matrices that I use are fairly small (around 6*6) and I only use 
> positive integers as elements.

Note that this is off-topic in comp.lang.c from where I am posting.
-> f'up2c.p

Some thoughts on your question:
- Do you want to restrict yourself to certain classes of permutations
or do you just want the matrix elements reordered in a random way?
- In the latter case, if you are programming in a language where you
know the memory layout and where the memory layout of the matrix is
essentially an array, you can just use (perfect) shuffling -- or,
if you need all permutations, a loop through all array permutations.
- Otherwise, just perform the effective action of the matrix-matrix
multiplication: Interchange the rows/columns of the target matrix as
intended.


Cheers
  Michael
-- 
E-Mail: Mine is an   /at/ gmx /dot/ de   address.

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