[Help-glpk] how to use prod?

[Shan Gao]

hi guys,

I am trying to use prod to calculate the production of numbers stored in an array x.

I wrote: prod {i in 1..5} x[i];    // same format with sum

but I was told  "integrand following prod{...} has invalid type".

it seems there is sth wrong with x[i]. (if i use i, everything will be fine.)

anybody know this?

thanks.

shan