Hi, I’m affraid that I’m not who answer the message, there must be another Daniel at Gamsworld
Best regards
2008/7/25 Gamsworld Admin
Daniel,
These statement would not compile (summation set d already controlled
on the equation index):
con1(d,h)… xdmin =l= sum(d, x(d,h) ) ;
con2(d,h)… xdmax =g= sum(d, x(d,h) ) ;
I guess you have
con1(h)… xdmin =l= sum(d, x(d,h) ) ;
con2(h)… xdmax =g= sum(d, x(d,h) ) ;
(don’t know if this makes sense).
You have to select one domain for your variable x. You used t and d,h.
I think you can savely work with just t. Assuming that the change from
above makes sense, you can rewrite these as follows:
con1(h)… xdmin =l= sum(tdh(t,d,h), x(t) ) ;
con2(h)… xdmax =g= sum(tdh(t,d,h), x(d,h) ) ;
Hope this makes sense to you.
Regards,
Michael Bussieck, GAMSWorld Coordinator
On Jul 23, 9:24 am, Daniel Wagner wrote:
Hello,
Thanks for you help. Very nice solution, but I was a little bit short
sighted and therefor I need a little more help.
I have data that is given with respect to sets d and h and my
variables are indexed by d and h, too. I need this because I have
constraints like this
con1(d,h)… xdmin =l= sum(d, x(d,h) ) ;
con2(d,h)… xdmax =g= sum(d, x(d,h) ) ;
on the other hand I also have the already mentionend constraints like,
where the lag/lead operators are needed.
con3a(t)… x(t) =e= x(t-1) + delta_i(t) - delta_d(t) ;
con3b(t)… deltamax =g= delta_i(t) + delta_d(t) ;
Is there a way to use the sets tdt and dht (of the previous message)
to ‘convert’ the indices?
Regards,
Daniel
On 18 Jul., 11:16, Gamsworld Admin wrote:
Daniel,
The GAMS lingo for this is lag and lead operators: x(d,h-1) e.g. shows
the previous hour. The ‘-’ is not a numercial minus but a lag. Trouble
is that the predecessor for x(d,‘h1’) is x(d-1,‘h24’). You also have
to decide what predecessor of ‘d1’,‘h1’ is. If you do a steady state
model you could have ‘d365’,‘h24’ or you can decide that there is no
predecessor (meaning delta(‘d1’,‘h1’) = x(‘d1’,'h1)). I am assuming
your sets look like this
set d / d1d365 /
h / h1h24 /
Now here is what you can do:
delta(d,h) =e= x(d,h) - x(d-(1$sameas(‘h1’)),h–1)) ;
Not so elegant, but it will work. I prefer working with an additional
set of all hours in the year:
and a map between d,h and all hours in the year:
sets h /h1*h24/, d /d1*d365/, dh(d,h) /#d.#h/
sets t /t1*t8760/, tdh(t,d,h) /#t:#dh/, dht/#dh:#t/
This matching operators (. and 
are new syntax and will work with
22.7 and higher. You can do the maps also with older GAMS statements.
Now I would have the variable x and delta over t and then the
constraint looks simple:
delta(t) =e= x(t) - x(t-1) (or x(t–1) for steady state)
In case you have data by d,h you can use the map tdh, for example:
delta(t) =l= sum(tdh(t,d,h), maxdeviation(d,h));
Hope this helps,
Michael Bussieck, GAMSWorld Admin
On Jul 18, 4:24 am, Daniel wrote:
Hello,
I’m new to GAMS (although not new to MIP programming) and hope I can
find help for a problem a currently have.
I have variables with two indices, e.g. x(d,h), where d and h are sets
of days and hours.
My problem is to make a predecessor/sucessor relation between those x
variables. E.g. I have to model the difference between two neighboring
x variables like:
delta(d,h) =e= x(d,h) - x(pred(d,h)) ;
delta(d,) =l= constant ;
Are there any ideas how to make this in an easy and elegant way?
Regards,
Daniel- Hide quoted text -
- Show quoted text -
–
Daniel Andrés Navia López
Mg.Sc.(c) Ciencias de la IngenierÃa Mención IngenierÃa QuÃmica
89674421
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