Nurse scheduling model formulation in AMPL - job-scheduling

Question

I have been working on a Nurse scheduling problem in AMPL for the following conditions:
Total no. of Nurses=20
Total no. of shits= 3 #morning,day,night
Planning Horizon 7 days: let's say M T W R F Sa Su
Along with following constraints:
Max no. of working days in a week: 5
A rest days after 4 continuous
night shifts.
Consecutive night and morning shifts are not allowed.
Demand per shift is 7 nurses.
A nurse can only work in one shift per day, i.e. morning, night, day
Cost scenarios:
Morning shift: $12
Day shift: $13
Night shift : $15
Objective function is to minimize the cost of operation as per Nurse preferences.
Can anyone give me an idea of how this problem can be formulated ?

Answer 1

So at first some things unusual in your problem definition:
This is not a real optimization problem, since your objective function is fixed per definition (every shift has 7 nurses, and every nurse has an equal price per shift)
In your Problem you defined 7 nurses per shift with a maimum of 5 working days. So you need 7 nurses on three shifts on seven days. This equals 147 nurse/shifts. But with the cap of five working days and only one shift per day, you just have 20 Nurses on 5 shifts, which equals to 100 nurse/shifts.
I've built the problem in Mathprog but the code should be more or less equal to AMPL. I've started with three sets for the nurses, days and shifts.
set shifts := {1,2,3};
set days := {1,2,3,4,5,6,7};
set nurses := {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};
The shedule is defined as a set of binary variables:
var schedule{nurses, days, shifts}, binary;
The simple objective contains the sum of all nurse/shifts in this week with the related prices:
minimize cost: sum{i in nurses, j in days}(schedule[i,j,1]*c_morning+schedule[i,j,2]*c_day+schedule[i,j,3]*c_night);
To your first constraint one can limit the sum of all shifts per nurse to five, since there is only one shift per day possible:
s.t. working_days{n in nurses}:
sum{i in days, j in shifts}(schedule[n,i,j]) <= 5;
The restday is the hardest part of the problem. For simplicity I've created another set which just contains the days, where a nurse could have achived four night-shifts in a row. You can also formulate the constraint with the original set of days and exclude the first four days.
set nigth_days := {5,6,7};
s.t. rest{n in nurses,i in nigth_days}:
(schedule[n,i-4,3]+schedule[n,i-3,3]+schedule[n,i-2,3]+schedule[n,i-1,3]+sum{j in shifts}(schedule[n,i,j])) <= 4;
For not having a morning-shift after a night-shift I used the same attempt like for the rest days. The seventh day is excluded, since there is no eigth day where we can look for a morning-shift.
set yester_days := {1,2,3,4,5,6};
s.t. night_morning{i in yester_days, n in nurses}:
(schedule[n,i,3]+schedule[n,i+1,1]) <= 1;
The demand of four nurses per shift should be met (I've reduced the number since more then 4 nurses are infeasible, due to the 5 shift limit)
s.t. demand_shift{i in days, j in shifts}:
sum{n in nurses}(schedule[n,i,j]) = 4;
The fifth constraint is to limit the shifts per day to a max of one.
s.t. one_shift{n in nurses, i in days}:
sum{ j in shifts}(schedule[n,i,j]) <= 1;

Answer 2

set nurse; #no. of full time employees working in the facility
set days; #planning horizon
set shift; #no. of shift in a day
set S; #shift correseponding to the outsourced nurses
set D;#day corresponding to the outsourced nurses
set N;#
# ith nurse working on day j
# j starts from Monday (j=1), Tuesday( j=2), Wednesday (j=3), Thursday(j=4), Friday(j=5), Saturday(j=6), Sunday(j=7)
#s be the shift as morning, day and night
param availability{i in nurse, j in days};
param costpershift{i in nurse, j in days, s in shift};
param outcost{n in N, l in D, m in S};
var nurseavailability{i in nurse,j in days,s in shift} binary; # = 1 if nurse i is available on jth day working on sth shift, 0 otherwise
var outsourced{n in N, l in D, m in S} integer;
#Objective function
minimize Cost: sum{i in nurse, j in days, s in shift} costpershift[i,j,s]*nurseavailability[i,j,s]+ sum{ n in N, l in D, m in S}outcost[n,l,m]*outsourced[n,l,m];
#constraints
#maximum no. of shifts per day
subject to maximum_shifts_perday {i in nurse,j in days}:
sum{s in shift} nurseavailability[i,j,s]*availability[i,j] <= 1;
#maximum no. of working says a week
subject to maximum_days_of_work {i in nurse}:
sum{j in days,s in shift} availability[i,j]*nurseavailability[i,j,s]<=5; #maximum working days irrespective of shifts
# rest days after night shifts
subject to rest_days_after_night_shift{i in nurse}:
sum{j in days} availability[i,j]*nurseavailability[i,j,3]<=4;
#demand per shift
subject to supply{j in days, s in shift, l in D, m in S}:
sum{i in nurse} availability[i,j]*nurseavailability[i,j,s] + sum{n in N} outsourced[n,l,m]=7;
#outsourcing only works well when there is more variability in supply.
#increasing the staff no. would be effective for reducing the cost variability in demand.
#considering a budget of $16,000 per week
#outsourcing constraints: a maximum of 20 nurses can be outsourced per shift
# no. of fulltime employees=30
#demand is 7 nurses per shift
#the average variability
#all nurses are paid equally # $12 per hour.
#cost of an outsourced shift is $144.
#cost of morning shift is $96.
#cost of day shift is $104.
#cost of night shift is $120.
data;
#set nurse ordered:= nurse1 nurse2 nurse3 nurse4 nurse5 nurse6 nurse7 nurse8
#nurse9 nurse10 nurse11 nurse12 nurse13 nurse14 nurse15 nurse16 nurse17
#nurse18 nurse19 nurse20;
set nurse:= 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30;
#set days ordered:= Monday Tuesday Wednesday Thursday Friday Saturday Sunday;
set days:= 1 2 3 4 5 6 7;
#set shift ordered:= Morning Day Night;
set shift:= 1 2 3;
set D:= 1 2 3 4 5 6 7; #outsourced days
set S:=1 2 3; #outshit
set N := 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20;
param outcost
[*,*,1]:
1 2 3 4 5 6 7:=
1 144 144 144 144 144 144 144
2 144 144 144 144 144 144 144
3 144 144 144 144 144 144 144
4 144 144 144 144 144 144 144
5 144 144 144 144 144 144 144
6 144 144 144 144 144 144 144
7 144 144 144 144 144 144 144
8 144 144 144 144 144 144 144
9 144 144 144 144 144 144 144
10 144 144 144 144 144 144 144
11 144 144 144 144 144 144 144
12 144 144 144 144 144 144 144
13 144 144 144 144 144 144 144
14 144 144 144 144 144 144 144
15 144 144 144 144 144 144 144
16 144 144 144 144 144 144 144
17 144 144 144 144 144 144 144
18 144 144 144 144 144 144 144
19 144 144 144 144 144 144 144
20 144 144 144 144 144 144 144
[*,*,2]:
1 2 3 4 5 6 7:=
1 144 144 144 144 144 144 144
2 144 144 144 144 144 144 144
3 144 144 144 144 144 144 144
4 144 144 144 144 144 144 144
5 144 144 144 144 144 144 144
6 144 144 144 144 144 144 144
7 144 144 144 144 144 144 144
8 144 144 144 144 144 144 144
9 144 144 144 144 144 144 144
10 144 144 144 144 144 144 144
11 144 144 144 144 144 144 144
12 144 144 144 144 144 144 144
13 144 144 144 144 144 144 144
14 144 144 144 144 144 144 144
15 144 144 144 144 144 144 144
16 144 144 144 144 144 144 144
17 144 144 144 144 144 144 144
18 144 144 144 144 144 144 144
19 144 144 144 144 144 144 144
20 144 144 144 144 144 144 144
[*,*,3]:
1 2 3 4 5 6 7:=
1 144 144 144 144 144 144 144
2 144 144 144 144 144 144 144
3 144 144 144 144 144 144 144
4 144 144 144 144 144 144 144
5 144 144 144 144 144 144 144
6 144 144 144 144 144 144 144
7 144 144 144 144 144 144 144
8 144 144 144 144 144 144 144
9 144 144 144 144 144 144 144
10 144 144 144 144 144 144 144
11 144 144 144 144 144 144 144
12 144 144 144 144 144 144 144
13 144 144 144 144 144 144 144
14 144 144 144 144 144 144 144
15 144 144 144 144 144 144 144
16 144 144 144 144 144 144 144
17 144 144 144 144 144 144 144
18 144 144 144 144 144 144 144
19 144 144 144 144 144 144 144
20 144 144 144 144 144 144 144;
param availability:
1 2 3 4 5 6 7 :=
1 0 0 0 0 0 0 0
2 1 1 1 1 1 1 1
3 1 1 1 1 1 1 1
4 1 1 1 1 1 1 1
5 1 1 1 1 1 1 1
6 1 1 1 1 1 1 1
7 1 0 1 1 1 1 1
8 1 1 1 1 1 1 1
9 1 1 1 1 1 1 1
10 1 1 1 1 1 1 1
11 1 1 1 1 1 1 1
12 1 1 1 1 1 1 1
13 1 1 1 1 1 1 1
14 1 1 1 1 1 1 1
15 1 1 1 1 1 1 1
16 1 1 1 1 1 1 1
17 0 1 1 1 1 1 1
18 1 1 1 1 1 1 1
19 1 1 1 1 1 1 1
20 1 1 1 1 1 1 1
21 1 1 1 1 1 1 1
22 1 1 1 1 1 1 1
23 1 1 1 1 1 1 1
24 1 1 1 1 1 1 1
25 1 1 1 1 1 1 1
26 1 1 1 1 1 1 1
27 1 1 1 1 1 1 1
28 1 1 1 1 1 1 1
29 1 1 1 1 1 1 1
30 1 1 1 1 1 1 1;
param costpershift:=
[*,*,1]: 1 2 3 4 5 6 7 :=
1 96 96 96 96 96 96 96
2 96 96 96 96 96 96 96
3 96 96 96 96 96 96 96
4 96 96 96 96 96 96 96
5 96 96 96 96 96 96 96
6 96 96 96 96 96 96 96
7 96 96 96 96 96 96 96
8 96 96 96 96 96 96 96
9 96 96 96 96 96 96 96
10 96 96 96 96 96 96 96
11 96 96 96 96 96 96 96
12 96 96 96 96 96 96 96
13 96 96 96 96 96 96 96
14 96 96 96 96 96 96 96
15 96 96 96 96 96 96 96
16 96 96 96 96 96 96 96
17 96 96 96 96 96 96 96
18 96 96 96 96 96 96 96
19 96 96 96 96 96 96 96
20 96 96 96 96 96 96 96
21 96 96 96 96 96 96 96
22 96 96 96 96 96 96 96
23 96 96 96 96 96 96 96
24 96 96 96 96 96 96 96
25 96 96 96 96 96 96 96
26 96 96 96 96 96 96 96
27 96 96 96 96 96 96 96
28 96 96 96 96 96 96 96
29 96 96 96 96 96 96 96
30 96 96 96 96 96 96 96
[*,*,2] : 1 2 3 4 5 6 7 :=
1 104 104 104 104 104 104 104
2 104 104 104 104 104 104 104
3 104 104 104 104 104 104 104
4 104 104 104 104 104 104 104
5 104 104 104 104 104 104 104
6 104 104 104 104 104 104 104
7 104 104 104 104 104 104 104
8 104 104 104 104 104 104 104
9 104 104 104 104 104 104 104
10 104 104 104 104 104 104 104
11 104 104 104 104 104 104 104
12 104 104 104 104 104 104 104
13 104 104 104 104 104 104 104
14 104 104 104 104 104 104 104
15 104 104 104 104 104 104 104
16 104 104 104 104 104 104 104
17 104 104 104 104 104 104 104
18 104 104 104 104 104 104 104
19 104 104 104 104 104 104 104
20 104 104 104 104 104 104 104
21 104 104 104 104 104 104 104
22 104 104 104 104 104 104 104
23 104 104 104 104 104 104 104
24 104 104 104 104 104 104 104
25 104 104 104 104 104 104 104
26 104 104 104 104 104 104 104
27 104 104 104 104 104 104 104
28 104 104 104 104 104 104 104
29 104 104 104 104 104 104 104
30 104 104 104 104 104 104 104
[*,*,3] : 1 2 3 4 5 6 7 :=
1 120 120 120 120 120 120 120
2 120 120 120 120 120 120 120
3 120 120 120 120 120 120 120
4 120 120 120 120 120 120 120
5 120 120 120 120 120 120 120
6 120 120 120 120 120 120 120
7 120 120 120 120 120 120 120
8 120 120 120 120 120 120 120
9 120 120 120 120 120 120 120
10 120 120 120 120 120 120 120
11 120 120 120 120 120 120 120
12 120 120 120 120 120 120 120
13 120 120 120 120 120 120 120
14 120 120 120 120 120 120 120
15 120 120 120 120 120 120 120
16 120 120 120 120 120 120 120
17 120 120 120 120 120 120 120
18 120 120 120 120 120 120 120
19 120 120 120 120 120 120 120
20 120 120 120 120 120 120 120
21 120 120 120 120 120 120 120
22 120 120 120 120 120 120 120
23 120 120 120 120 120 120 120
24 120 120 120 120 120 120 120
25 120 120 120 120 120 120 120
26 120 120 120 120 120 120 120
27 120 120 120 120 120 120 120
28 120 120 120 120 120 120 120
29 120 120 120 120 120 120 120
30 120 120 120 120 120 120 120;