Hi,
Thanks for your reply.
I really, really wasn't expecting this sort of reply. I'm now in the
uncomfortable position of trying to decide exactly what I DO mean :+)
To put the problem into a clearer perspective, it concerns 3 variables
A,B and C.
A is a FD integer which represents a virtual actor, B is a FS which
represents one or more other virtual actors.
C is a FD integer which represents an interaction which is possible
between virtual actors depending upon characteristics of those agents.
At the moment I'm using the format:
thread
if C==x then
<post constraints on A and B to match interaction x>
end
end
My thought was that I could possibly make speed improvements on this by
replacing the 'if' statement with something which would cause the thread
to fail sooner - namely the (C==x)=true idea.
Now I'm struggling to decide if saying something completely different
semantically by doing this will fundamentally alter the function of my
program or even whether I'm structuring my problem logic correctly in
the first place.
I think some more thought on this might be in order :+)
Regards
Mark
Raphael Collet wrote:
Dear Mark,
Your two threads simply implement different semantics! See below:
On Sun, Jul 19, 2009 at 10:05 PM, mark richardson
<[email protected] <mailto:[email protected]>> wrote:
Hi,
I have a constraint based problem that implements constraints as
explicitly defined threads. An if statement guards whether the
constraint is imposed or not. For example one of the constraints
could be something like:
thread
if B==2 then
<post some constraint>
end
end
This threads tries to enforce the logic statement (B==2 and
<constraint>) or (B\=2). If B is different from 2, the logic
statement is equivalent to 'true'.
My program isn't as simple as this and there IS a good reason why
I'm doing things this way :+), but it demonstrates the basic idea.
My question is this (although I can't think of a simplified
example to test it with); would the above code block prove more
efficient like this:
thread
(B==2)=true
<post some constraint>
end
This second threads enforces the logic statement (B==2 and
<constraint>). In this case, if B is different from 2, the logic
statement is equivalent to 'false'. Therefore both threads are not
equivalent from a logic point of view.
Here I'm assuming this thread would signal failure whenever B was
not 2 and subsequently fail the space it was in.
In other words, are there any efficiency gains to be made by using
failure as a guard for the constraint rather than a logic
conditional statement? (Obviously I'm talking about a very large
number of calls to this thread.)
The first question is: which of the two logic statements correspond to
the problem?
For the first semantics, it is possible to use an 'or' statement, and
let the posted constraint be evaluated in a subspace.
or B=2 <post some constraint>
[] B\=:2
end
If the posted constraint fails, the 'or' statement will automatically
enforce the remaining clause, i.e., B\=2. Note that this technique
should be used with care, because it creates more computation spaces,
but it can pay off if the posted constraint is likely to fail...
Cheers,
raph
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Mark Richardson
Research Assistant
University of Teesside, UK
[email protected]
[email protected]
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