Hello Andrew,
>> In principle, you might create a numeric set, say, {1, 2, 3}, and
>> then use its elements as indices to a symbolic parameter.
The symbolic values in my case will be read from a SQL table.
Your solution would require a function to determine the index of a value
in a (symbolic) set:
set S;
table ts IN 'MySQL' dsn table : S <- [S];
set N := setof{s in S} index(s, S);
If such a function existed I could change my example to:
set J;
set B := setof{j1 in J, j2 in J : index(j1, J) < index(j2, J)} (j1, j2);
display B;
data;
set J := 'A' 'B';
I would prefer to be able to directly compare symbols.
Please, find my implementation as:
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.28-strcmp/src/glpmpl01.c
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.28-strcmp/src/glpmpl03.c
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.28-strcmp/examples/strcmp.mod
Patches are available as:
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.28-strcmp/src/glpmpl01.c?r1=228&r2=202&view=patch
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.28-strcmp/src/glpmpl03.c?r1=228&r2=202&view=patch
>> Yes, I think it would be useful to add some built-in functions to
>> perform operations on symbolic values.
AMPL provides the following functions for symbols:
length(symbol) returns the number of characters,
match(symbol, regexp) returns the first match for the regular expression
regexp in symbol,
symbol1 & symbols2 returns the concatenation of the strings,
sprintf("format", arg1, ...) uses the C sprintf function to create a
formatted string,
sub(symbol1, regexp, symbol2) returns a string where the first match of
the regular expression is replaced by symbol2,
gsub(symbol1, regexp, symbol2) returns a string where the all matches of
the regular expression is replaced by symbol2,
substr(symbol, pos) returns the subtring of symbol starting with
character position pos,
substr(symbol, pos, len) returns the subtring of lenght len of symbol
starting with character position pos,
Best regards
Xypron
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