[FlopCpp] Question on indexing constraints

[Tim Hultberg]

Hi Michal,
   flopc++ is "GAMS-influenced" in the sense that sets can act as
indices, but "AMPL-influenced" in the sense that you dont have to use
sets as indices. [ sum(S, ...) is just a shorthand notation for
sum(S(S),...) where the first S acts as a set and the second S acts as
an index]

Looking at your example, I see that the real problem is NOT the use of
sets or indices, but rather that you are using the wrong number of
indices (no matter whether declared as MP_index or MP_set).

For example, after declaring MP_data dAB3(AB) you shouldnt reference it
with two indices as in dAB3(A,B) [so why doesnt flopc++ complain nor at
compilation time nor at runtime? Thats a long story, if I get time I'll
add more about this at the end of the mail*]

This (using the wrong number of indices) explains most of your "not
working" cases. Except:

a)The second group (with forall) where in fact all 3 examples "works",
you just forgot to use dBC2 and dBC3 in the last two examples.

b)		cABC1(AB,C)  =  xAC(A,C) + xABC(AB,C) == dBC(B,C);
here the number of the indices are ok, but A and B are not bound. There
is absolutely no static association of indices to sets in flopc++
(allthough the shorthand notation mentioned before might give you that
impression) so you need to tell what indices to are bound to the subsets
of AB as you do correctly one line above.

c)    cAs2(As)  =  xA(As) <= dA(As);
here As is bound but indexing is based on subset indices not the
corresponding superset indices (i.e if  As={5,9} As will be bound to 0
and 1, not to 5 and 9. If both is needed, use cAs2(As(A))).
[If xA and dA are not used anywhere else you could of course also
declare them over the subset, then this would be ok]

Summing up: this could (should) be documented if I'll get ever get some
time for making better doc. flopc++ error handling (when for example
using wrong number of indices) could be improved [but there are some
tricky issues here]. 

Anyway I hope this helps you understand whats going on.

Slow compilation: a lot of code is the hpp files which could be moved
to cpp to spped up compilation.

"eval subsetref"; oops. some debug stuff committed by mistake, removed
in stable now

Cheers, Tim






>>> Michal Kaut <mail at michalkaut.net> 11/06/2007 10:14 >>>
Hello,

I forgot to attach the example file to my previous email, so I am 
sending it again - so please ignore the previous one. I apologize for 
any inconvenience...


I have been struggling to understand the indexing of FlopC++
constraints
and must admit I still do not understand it properly. What confuses me
most is that for each type of constraints I wanted to test, I was able
to find several "seemingly equivalent" formulations, all of which
compile, but only one of which gives the expected results.

I have tried to demonstrate it on the attached example, where the
constraints with a name differing only in number are supposed to do
the
same thing, but only those that have "WORKS" in the comment actually
generate the expected result. (I should probably confess that I am an
AMPL user, so I have probably different understanding what an "index"
means, compared to the GAMS-influenced designers of FlopC++.)
- Could someone try to explain to me why the bad formulations do not
work, i.e. what they actually do? (They do something, as they
compile.)
- Note that the example is only to illustrate indexing, the resulting
model is not supposed to make any sense.


In addition, I was rather disappointed by the compilation speed (i.e.
the lack of it): this very small example takes over a minute to
compile
on mu 3GHz Pentium 4 machine with gcc 3.4.5 (mingw on WinXP).
Of this time, 39 seconds are spend on the last three sets of
constraints
(getIndx1-3), i.e. the compile+link time is 26 seconds without those
constraints. Is this normal/expected behaviour?
(Another interesting thing is that adding each of the three sets of
constraints individually adds 5s, 10s and 10s respectively, i.e. 25
seconds in total, while adding all three adds 39 seconds to the
compilation time...)


And one more question: is it possible to get rid of the "eval
subsetref"
messages? Even with this small example, I get hundreds of them and
setting model.silent() does not switch them off...


Thanks a lot in advance.

Regards,
Michal Kaut