AMPL - param that maps from set to set

Question

I'm new to AMPL, and I would like to create a param C that map from a set A to set B:

file.mod:

set A;
set B;
param C{i in A} =
    if i == "AA"
    then
        BA
    else if i == "AB"
    then
        BB
    else if i == "AC"
    then
        BC
    else
        BA;

data file.dat;

file.dat:

data;

set A := AA, AB, AC;
set B := BA, BB, BC;

When I try to compile this code, I get BA is not defined. If I replace the set element by string (BA becomes "BA"), then the error `Cannot convert character string to a number.``showed up. Is there a way to achieve what I want to do?

Answer 1

Parameters in AMPL default to number. If you want to set a string parameter, you have to declare it as symbolic. (And yes, you need the quotes on those values.)

This seems to do what you want:

set A;
set B;
param C{i in A} in B symbolic =
    if i == "AA"
    then
        "BA"
    else if i == "AB"
    then
        "BB"
    else if i == "AC"
    then
        "BC"
    else
        "BA";

 data;

 set A := AA, AB, AC;
 set B := BA, BB, BC;

See section 7.8 of the AMPL Book for more information about symbolic parameters.