Add IIS example code, ref jump-dev#235

examples/iis.jl

@@ -0,0 +1,73 @@
+#############################################################################
+# JuMP
+# An algebraic modelling langauge for Julia
+# See http://github.com/JuliaOpt/JuMP.jl
+#############################################################################
+# iis.jl
+#
+# Extract an Irreducible Inconsistent Subsystem (IIS)
+# from an infeasible model.
+# This code is specific to Gurobi.
+#############################################################################
+
+using JuMP, Gurobi
+import MathProgBase
+
+function print_iis_gurobi(m::Model)
+
+    grb = MathProgBase.getrawsolver(getInternalModel(m)) 
+    Gurobi.computeIIS(grb)
+    numconstr = Gurobi.num_constrs(grb)
+    numvar = Gurobi.num_vars(grb)
+
+    iisconstr = Gurobi.get_intattrarray(grb, "IISConstr", 1, numconstr)
+    iislb = Gurobi.get_intattrarray(grb, "IISLB", 1, numvar)
+    iisub = Gurobi.get_intattrarray(grb, "IISUB", 1, numvar)
+
+    println("Irreducible Inconsistent Subsystem (IIS)")
+    println("Variable bounds:")
+    for i in 1:numvar
+        v = Variable(m, i)
+        if iislb[i] != 0 && iisub[i] != 0
+            println(getLower(v), " <= ", getName(v), " <= ", getUpper(v))
+        elseif iislb[i] != 0
+            println(getName(v), " >= ", getLower(v))
+        elseif iisub[i] != 0
+            println(getName(v), " <= ", getUpper(v))
+        end
+    end
+
+
+    println("Constraints:")
+    for i in 1:numconstr
+        if iisconstr[i] != 0
+            println(m.linconstr[i])
+        end
+    end
+    println("End of IIS")
+end
+
+# The function below produces the following output:
+#=
+Irreducible Inconsistent Subsystem (IIS)
+Variable bounds:
+x <= 1.0
+y <= 1.0
+Constraints:
+x + y >= 3
+End of IIS
+=#
+
+function iis_example()
+    m = Model(solver=GurobiSolver())
+
+    @defVar(m, 0 <= x <= 1)
+    @defVar(m, 0 <= y <= 1)
+
+    @addConstraint(m, x+y >= 3)
+
+    status = solve(m)
+    @assert status == :Infeasible
+
+    print_iis_gurobi(m)
+end