Param, same value for multiple parameters

[ransomkan]

Hi,

Suppose I have param b{J,K}, 

param b:
    1 2 3 4 5 :=
1 1 2 3 2 5

2 1 3 4 9 6

3 1 2 8 6 4;

and notice that b[j ,1] =1 for all j in J. is there a way to write it separately,

param b[,1]=1 and 

param b:
    2 3 4 5 :=
1 2 3 2 5

2 3 4 9 6

3 2 8 6 4;

to save some space for large data files?

Thank you so much. 

[AMPL Google Group]

You can specify a default value of 1 for your data statement:

param b default 1:
  2 3 4 5 :=
1 2 3 2 5
2 3 4 9 6
3 2 8 6 4;

Then when b is used (for example when you solve), any missing entries in b will be given the value 1. There can be only one default value for a parameter's data, however. Another approach is to read

param b:
  2 3 4 5 :=
1 2 3 2 5
2 3 4 9 6
3 2 8 6 4;

and then assign the missing entries with AMPL assignment statements like this:

let {j in J} b[j,1] := 1;

This is more general, since you can have any number of assignments of various values. (Note that if your "let" statement appears in the middle of a data file, you should follow it with a "data;" statement to switch AMPL back to "data mode".)

--
Robert Fourer
am...@googlegroups.com

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