Merge pull request #479 from JuliaOpt/mpbidx

implement getLinearIndex

doc/refvariable.rst

@@ -95,7 +95,7 @@ This form of constructing variables is not considered idiomatic JuMP code.
     The reference to the first set of variables has been lost, although they will remain
     in the model.
 
-Finally, the constructor ``Variable(m::Model,idx::Int)`` may be used to create a variable object corresponding to an *existing* variable in the model (the constructor does not add a new variable to the model). The variable indices correspond to those of the internal MathProgBase model. This method is only useful if you intend to interact with solver properties which are not directly exposed through JuMP.
+Finally, the constructor ``Variable(m::Model,idx::Int)`` may be used to create a variable object corresponding to an *existing* variable in the model (the constructor does not add a new variable to the model). The variable indices correspond to those of the internal MathProgBase model. The inverse of this operation is ``getLinearIndex(x::Variable)``, which returns the flattened out (linear) index of a variable as JuMP provides it to a solver. We guarantee that ``Variable(m,getLinearIndex(x))`` returns ``x`` itself. These methods are only useful if you intend to interact with solver properties which are not directly exposed through JuMP.
 
 Semidefinite and symmetric variables
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/JuMP.jl

@@ -34,6 +34,7 @@ export
     setName, getName, setLower, setUpper, getLower, getUpper,
     getValue, setValue, getDual, setCategory, getCategory,
     getVar,
+    getLinearIndex,
     # Expressions and constraints
     affToStr, quadToStr, conToStr, chgConstrRHS,
 
@@ -223,7 +224,8 @@ immutable Variable <: ReverseDiffSparse.Placeholder
     col::Int
 end
 
-ReverseDiffSparse.getplaceindex(x::Variable) = x.col
+getLinearIndex(x::Variable) = x.col
+ReverseDiffSparse.getplaceindex(x::Variable) = getLinearIndex(x)
 Base.isequal(x::Variable,y::Variable) = isequal(x.col,y.col) && isequal(x.m,y.m)
 
 Variable(m::Model, lower, upper, cat::Symbol, name::String="", value::Number=NaN) =

test/model.jl

@@ -601,3 +601,11 @@ facts("[model] Setting print hook") do
     print(m)
     @fact dummy => [2]
 end
+
+facts("[model] Test getLinearIndex") do
+    m = Model()
+    @defVar(m, x[1:5])
+    for i in 1:5
+        @fact isequal(Variable(m,getLinearIndex(x[i])),x[i]) => true
+    end
+end