[AMPL 24822] Fixing my Ampl code

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1

I need help with this problem
you run a small company providing napkins for hotels. For
each of the next 5 days you know how many napkins you’ll
need: 80, 70, 120, 150, 100, respectively. Each morning
when delivering your napkins, you can pick up the used
ones (what you delivered previous day). If you send those
(or some of those) for a cleaning (for $a/napkin) than they
can be used as new ones at the next morning delivery. You
can also buy new napkins at $b/napkin any given day,
before you make the deliveries for that day. You can also
keep clean (new) napkins in your stock for $c/day/napkin
for following days. Initially you have 100 napkins in stock.
Create a model to find a cost minimal plan (of
buying/cleaning/storing) to fulfill your contract (for the
next 5 days) create a .dat and .mod file

Here is my dat file

data

param n := 5;

param demand :=

1 80

2 70

3 120

4 150

5 100;

param cost_cleaning := 0.50; # Set the actual cleaning cost here

param cost_new := 0.75; # Set the actual cost of buying new napkins here

param cost_stock := 0.10; # Set the actual cost of storing napkins here

here is my mod file

param n; # Number of days

set Days := 5;

param demand{Days};

param cost_cleaning;

param cost_new;

param cost_stock;

param initial_stock := 100; # Initial stock of napkins

var x{Days} >= 0; # Number of napkins bought on each day

var y{Days} >= 0; # Number of napkins cleaned on each day

var s{Days} >= 0; # Number of napkins kept in stock after each day

Objective function: Minimize the total cost

minimize TotalCost:

cost_new * sum {d in Days} x[d] +

cost_cleaning * sum {d in Days} y[d] +

cost_stock * sum {d in Days} s[d];

subject to DemandConstraint {d in Days}:

s[d] + initial_stock + x[d] = demand[d] + y[d];

The number of napkins in stock cannot be negative

s.t. NonNegativeStock {d in Days}:

s[d] >= 0;

Variables representing buying and cleaning cannot be negative

s.t. NonNegativeBuys {d in Days}:

x[d] >= 0;

s.t. NonNegativeCleaning {d in Days}:

y[d] >= 0;

Solve the LP model

data SAHC-hw4.dat;

option solver cplex;

solve;

display x;

display y;

display s;

display TotalCost;

i keep getting this error

n is already defined

context: param >>> n; <<< # Number of days

ampl:

please help me ASAP

2

Your statement “set Days := 5;” gives an error message, because 5 is a number, not a set. Instead, since you have already defined param n to be the number of days, you should write

set Days := 1..n;

which says that Days is the set of all integer numbers from 1 to n.

If you read the model and data, and then you decide to make some changes, be sure to give the command “reset;” before reading the model and data again. If you forget “reset;” then you will get an “n is already defined” error.

3

Actually I have come up with a new dat and mod file. but I am still getting errors. Please use the problem I sent as reference.

I do not know what is going on

set Days := 1,2,3,4,5; # Number of days

param d :=

1 80

2 70

3 120

4 150

5 100;

param a := 1; # Cost per napkin for cleaning

param b := 2; # Cost per napkin for buying new napkins

param c := 0.5; # Cost per day for storing clean napkins

param stock_init := 100; # Initial number of napkins in stock

Mod file

param d{1…n}; # Number of napkins needed each day

param a; # Cost per napkin for cleaning

param b; # Cost per napkin for buying new napkins

param c; # Cost per day for storing clean napkins

param stock_init; # Initial number of napkins in stock

var Buy{1…n} integer >= 0; # Number of napkins bought each day

var Clean{1…n} integer >= 0; # Number of napkins cleaned each day

var Stock{0…n} integer >= 0; # Number of napkins in stock at the end of each day

minimize sum(i in 1…n, aClean[i] + bBuy[i] + c*Stock[i]);

subject to NapkinBalance{i in 1…n}:

Stock[i-1] + Buy[i] + Clean[i] = d[i] + Stock[i];

subject to StockInit: Stock[0] = stock_init;

solve;

for i in 1…n do

printf “Day %d: Buy %d, Clean %d, Stock %d\n”, i, Buy[i], Clean[i], Stock[i];

endfor;

I am still not getting the desired result and I do not know what is going wrong

4

I am still getting an error. This time it is telling me

syntax error

context: >>> param <<< demand{DAYS}; # Demand for napkins on each day

ampl:

Here is my mod file:

reset;

set Days # Define the set of days

param demand{DAYS}; # Demand for napkins on each day

param cost_cleaning; # Cost per napkin for cleaning

param cost_purchase; # Cost per napkin for purchasing

param cost_stock; # Cost per napkin for stock

param initial_stock; # Initial stock of napkins

var buy{DAYS} >= 0; # Number of napkins to purchase on each day

var clean{DAYS} >= 0; # Number of napkins to send for cleaning on each day

var stock{DAYS} >= 0; # Number of napkins to stock for each day

minimize TotalCost:

sum {d in DAYS} cost_cleaning * clean[d] + cost_purchase * buy[d] + cost_stock * stock[d];

subject to StockBalance {d in DAYS}:

stock[d] = (initial_stock + buy[d] - clean[d]) - demand[d];

option solver cplex;

data SAHC-hw4.dat;

solve;

display buy;

display clean;

display stock;

Here is my dat file:

set DAYS := 1 2 3 4 5;

param demand :=

1 80

2 70

3 120

4 150

5 100;

param cost_cleaning := a; # Replace with the actual cost per napkin for cleaning

param cost_purchase := b; # Replace with the actual cost per napkin for purchasing

param cost_stock := c; # Replace with the actual cost per napkin for stock

param initial_stock := 100; can you please help me so that i can solve the napkin problem?