Description

Lag and lead operations require the reference set to  be ordered and
constant. In some special cases one would want to use those operation on dynamic
and/or unordered sets. A DCO option on/offOrder has been added to locally relax
the default requirements. The use of this option comes with a price, the system
will not be able to diagnose odd and incorrect formulations and data sets.

A small example will be used to illustrate the use of $onOrder and $offOrder. We
would like to have a circular lead on the content of a slice as shown below.

Small Model of Type : GAMS

Category : GAMS Test library

Main file : lagd1.gms

$Title 'Lag and Lead operations on Dynamic Sets' (LAGD1,SEG=560)

$ontext
Lag and lead operations require the reference set to  be ordered and
constant. In some special cases one would want to use those operation on dynamic
and/or unordered sets. A DCO option on/offOrder has been added to locally relax
the default requirements. The use of this option comes with a price, the system
will not be able to diagnose odd and incorrect formulations and data sets.

A small example will be used to illustrate the use of $onOrder and $offOrder. We
would like to have a circular lead on the content of a slice as shown below.
$offtext

set a / a1,a2,a3 /, c /c1*c7 /, ac(a,c) / a1.(c2   ,c3   ,c5),    a3.c3 /
    desiredacc(a,c,c) circular lead     / a1.(c2.c3,c3.c5,c5.c2), a3.c3.c3 /
    acc(a,c,c), wrongacc(a,c,c);

wrongacc(ac(a,c),c++1) = yes; display wrongacc;

* the above assignment will not work because the lead operator is relative to
* the set c. we do need to extract the content of the second index position to
* be used as a reference set and relax the requirement to have a ordered and/or
* dynamic reference sets.

set temp(c);

$offOrder
loop(a,
   temp(c) = ac(a,c);
   acc(ac(a,temp),temp++1) = yes);
$onOrder

* arrange the display in list format
option ac:0:0:1,acc:0:0:1; display ac,acc;