[Paul_Diraq]

The problem with the algorithms faster than conventional mm is, that they are defined on mathematical numbers.

E.g. strassens-algorithms assumes something like:

(A+B)C - BC = AC

With the convential floating point representation this becomes a problem if B >> A because of rounding errors.

Most algorithms faster than Strassen assume:

(( fA + B)C - BC)/f = AC

and

(fA + B)C = BC +fAC

f is then choosen in such a way, that fAC is neglegible. But if that is the case fA is much smaller than B and we automatically get numerical problems.

There is a procedure to remove the fAC terms (which would imply that f could be choosen close to 1) which armortizes over enough recursions. But for Coppersmith-Winograd (and derivatives like Le-Galls algorithm). We need to divide the matrix in each recursion step into enough submatrices that the indices can be treated heuristically(lets say a division of each index in each iteration in 100 subindices). This would imply the sides of each matrix must be at least of size 100^n_recusion. We won't need to multiply matrices of that size.

[geezerjay]

Thank you for posting your comment. Very insightful and packed with goodies!