[OT] Use case for a 4-D matrix

[Tomek Sowiński]

Dnia 04-09-2010 o 08:03:12 John Demme <jdd at cs.columbia.edu> napisał(a):

> As for the graphs, I essentially take two input graphs, represented in
> adjacency matrix form (two 2-d matrices of size n^2 each, assuming equal
> sized graphs).  Then, I compute the Kronecker Tensor Graph Product[2],  
> which
> creates a matrix of size n^4.  Depending on how you think about it, this
> matrix is a simple (although large) 2-D adjacency matrix of the product
> graph, and it can be treated as such for many operations.  It can also be
> inspected in four dimensional space to examine the relationships between
> possible node pairs, but I don't do this.  Frankly, it hurts my brain a
> little bit.

Can't you compute the Kronecker product lazily? E.g. a proxy object that  
computes a value in an overloaded opIndex. Even if your algorithms inspect  
(compute) the same value several times, you may still win -- the  
bottleneck these days is memory access, not CPU cycles.

Fascinating stuff you're dealing with... Good luck.

Tomek