1 files changed, 145 insertions, 0 deletions
diff --git a/assignment.py b/assignment.py
new file mode 100755
index 0000000..61f7d62
--- /dev/null
+++ b/assignment.py
@@ -0,0 +1,145 @@
+#!/bin/python
+import glpk
+import os
+import re
+import toml
+import sys
+import math
+import random
+
+random.seed(1409)
+# 1 input parameter, the input filename
+
+if len(sys.argv) < 2:
+    print("Usage: assignment.py <configuration.toml>")
+    sys.exit(-1)
+
+with open(sys.argv[1]) as f:
+    tm = toml.load(f)
+
+if not ("students" in tm):
+    print(f"Missing table students with preferences in {sys.argv[1]}, e.g.\n[students]\n# Student a@abc.de preferes topic 2 over 6 over 4.\n\"a@abc.de\": [2,6,4]")
+    sys.exit(-1)
+
+students = tm['students']
+print("#Students = ",len(students))
+m = 0
+mlen = 0
+for s in students.keys():
+    m = max(m,max(students[s])+1)
+    mlen = max(mlen, len(students[s])-1)
+
+topics = [x for x in range(0,m)]
+
+interest_decay = lambda x,y: x/math.pow(2,y)
+factor = math.pow(2,mlen)
+function="exponential"
+if "settings" in tm:
+    if "interest_decay" in tm["settings"]:
+        if tm["settings"]["interest_decay"] == "lin":
+            interest_decay = lambda x,y: x-y
+            factor = mlen+1
+            function="linear"
+
+
+lp = glpk.LPX()                         
+lp.name = 'assignment'                  
+lp.obj.maximize = True                  
+lp.rows.add(len(students)+len(topics))
+objective=[]
+constraints=[]
+for idx,(s,r) in enumerate(zip(students.keys(),lp.rows[:len(students)])):
+    r.name = 'student %s' % s
+    # Each student gets exactly one topic
+    r.bounds = 1.0,1.0
+    last = 0
+    beg = 0
+    while beg<idx*len(topics):
+        constraints.append(0.0)
+        beg+=1
+    comp = [(idx,val) for idx,val in enumerate(students[s])]
+    comp = sorted(comp, key=lambda x: x[1])
+    for (dv,k) in comp:
+        while last < k:
+            objective.append(0.0)
+            constraints.append(0.0)
+            last+=1
+        objective.append(interest_decay(factor, dv))
+        constraints.append(1.0)
+        last+=1
+    while last < len(topics):
+        objective.append(0.0)
+        constraints.append(0.0)
+        last+=1
+    beg = (idx+1)*len(topics)
+    while beg < len(students)*len(topics):
+        constraints.append(0.0)
+        beg+=1
+
+for e,r in enumerate(lp.rows[len(students):]):                       
+    r.name = 'topic %s' % e
+    # subject must be chosen at most 1 time.
+    r.bounds = 0.0,1.0
+    beg = 0
+    while beg < len(students)*len(topics):
+        if beg%len(topics) == e:
+            constraints.append(1.0)
+        else:
+            constraints.append(0.0)
+        beg+=1
+lp.cols.add(len(students)*len(topics))                          
+for c in lp.cols:                       
+    c.name = 'x_%d_%d' % (c.index//len(topics),c.index%len(topics))            
+    c.bounds = 0.0, 1.0
+lp.obj[:] = objective
+iteration = 0
+optimal_solutions = []
+best_solution = 0
+while True:
+    lp.matrix = constraints
+    retval = lp.simplex()
+    assert retval is None
+    if lp.status != 'opt':
+        break
+    for col in lp.cols:
+        col.kind = int
+
+    retval = lp.integer()
+
+    assert retval is None
+
+    if lp.status != 'opt':
+        break
+    if lp.obj.value < best_solution:
+        break
+    else:
+        best_solution = lp.obj.value
+    next_constraint = []
+    current_solution = []
+    for c in lp.cols:
+        if c.primal == 1:
+            first = c.name.find("_")
+            end = c.name.find("_", first+1)
+            idx = int(c.name[first+1:end])
+            next_constraint.append(1.0)
+            current_solution.append((list(students.keys())[idx], c.name[end+1:]))
+        else:
+            next_constraint.append(0.0)
+    lp.rows.add(1)
+    r = lp.rows[-1]
+    r.name = 'exclude %s' % iteration
+    r.bounds = 0.0,len(students)-1
+    iteration+=1
+    # Add cutting plane
+    constraints.extend(next_constraint)
+    optimal_solutions.append(current_solution)
+
+if len(optimal_solutions) == 0:
+    print("Unsolvable assignment!")
+    sys.exit(-1)
+print("#Optimal Solutions = {0}; objective weight = {1:.6}; {2} scoring".format(len(optimal_solutions), best_solution, function))
+print("Uniform choice among optimal solutions:")
+opt = random.choice(optimal_solutions)
+for (stud,choice) in opt:
+    print("{0:<40} Topic {1}".format(stud, choice))
+