In my AMPL code, I want to use a variable whose value will be between 0 and 1. It can be any fraction between 0 and 1(0 and 1 inclusive). How can I declare such variable in AMPL and use it? I would be grateful if anyone provide me an example AMPL code for fractional knapsack problem.
I have written this code in AMPL and and tried to run in Neos Server. It is showing me all my variables x[i,j]=0 in the result but it is not the optimal solution. When I am using var x{i in 1..consumer, j in 1..source} binary;, it is giving the optimal result. But in my optimization problem, a consumer can derive energy from multiple sources and can take any fraction from the available energy of the sources. So, my variable must be 0<=x<=1
Can anyone find out what's the problem here? Thanks.
My .mod file is:
param source;
param consumer;
param max_cost;
param max_unit;
param available{j in 1..source};
param demand{i in 1..consumer};
param unit_cost{j in 1..source};
param fi{i in 1..consumer,j in 1..source};
var x{i in 1..consumer, j in 1..source};
minimize total: sum{i in 1..consumer, j in 1..source} ((0.5 * ((unit_cost[j] * x[i,j] * available[j]) / (max_cost * max_unit))) + (0.5 * fi[i,j] * ceil(x[i,j])));
subject to sell{j in 1..source}: sum{i in 1..consumer} x[i,j] <= 1;
subject to limita{i in 1..consumer, j in 1..source}:x[i,j] >=0;
subject to limitb{i in 1..consumer, j in 1..source}: x[i,j] <=1;
subject to dem{i in 1..consumer}: sum{j in 1..source} ( x[i,j] * available[j]) >= demand[i];
My .dat file is:
param source:= 2;
param consumer:= 1;
param max_cost:= 60;
param max_unit:=100;
param available:= 1 10
2 50;
param unit_cost:= 1 0
2 20;
param fi: 1 2 :=
1 0.3 0.05;
param demand:= 1 30;
instead of
var x{i in 1..consumer, j in 1..source};
you should write
var x{i in 1..consumer, j in 1..source}>=0,<=1;