UniverseAlias

Example - Creating an alias for the Universe

In GAMS, it is possible to create aliases to the universe (i.e., the entire list of UELs) with the syntax:

set i / i1, i2 /;
alias(h,*);
set j / j1, j2 /;

GAMS Transfer R allows creating aliases to the universe set.

In this small example, h would be associated with all four UELs (i1, i2, j1 and j2) even though set j was defined after the alias declaration. GAMS Transfer mimics this behavior with the UniverseAlias class. Internally, the records attribute will always call the <Container>$getUELs(). The UniverseAlias class is fundamentally different from the Alias class because it does not point to a parent set object. It is not possible to perform operations (like setRecords or findDomainViolations) on the parent set through a UniverseAlias (because there is no parent set object). This means that a UniverseAlias can be created by only defining the symbol name. We can see this behavior in the following example:

library(gamstransfer)
m <- Container$new()
i <- Set$new(m, "i", records = c("i1", "i2"))
h <- UniverseAlias$new(m, "h")
j <- Set$new(m, "j", records = c("j1", "j2"))

> m$listSymbols()
[1] "i" "h" "j"

> m["h"]
GAMS Transfer: R6 object of class UniverseAlias.
    Use h$summary for details

> h$records
uni
1 i1
2 i2
3 j1
4 j2

Note

Unlike other sets, the universe does not hold on to set element_text, thus the returned data frame for the UniverseAlias will only have one column.