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paralell assignment problem
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Date: 2005-02-08 (03:07)
From: skaller <skaller@u...>
Subject: paralell assignment problem
Does anyone know how to solve the parallel assignment problem?
Name invented by me to describe this problem:

x1,x2,x3..xn = e1,e2,e3 .. en

where ei might contain the variables xj. (Note = here is assignment).

The solution is a sequence of assignments involving
only xi, ei, and ti, where ti are temporaries introduced
to save the values of the expressions. For example,
a solution to

	x,y = y,x


	t = x; x = y; y = t

I seek a solution which minimises the number of assignments.
Note that the relation 

	i < j == ej doesn't depend on xi

is not transitive. This (a) confuses me enough I can't
see the solution, and (b) is precisely what allows
a temporary to remove a dependence.

John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net