SplitFreeVars: Preserve var order

src/Cuts/tableau/transform.jl

@@ -179,71 +179,55 @@ end
 # -----------------------------------------------------------------------------
 
 Base.@kwdef mutable struct SplitFreeVars <: Transform
-    F::Int = 0
-    B::Int = 0
-    free::Vector{Int} = []
-    others::Vector{Int} = []
+    ncols::Int = 0
+    is_var_free::Vector{Bool} = []
 end
 
 function forward!(t::SplitFreeVars, data::ProblemData)
     lhs = data.constr_lhs
     _, ncols = size(lhs)
-    free = [i for i = 1:ncols if !isfinite(data.var_lb[i]) && !isfinite(data.var_ub[i])]
-    others = [i for i = 1:ncols if isfinite(data.var_lb[i]) || isfinite(data.var_ub[i])]
-    t.F = length(free)
-    t.B = length(others)
-    t.free, t.others = free, others
+    is_var_free = [!isfinite(data.var_lb[i]) && !isfinite(data.var_ub[i]) for i = 1:ncols]
+    free_idx = findall(is_var_free)
     data.obj = [
-        data.obj[others]
-        data.obj[free]
-        -data.obj[free]
+        data.obj
+        [-data.obj[i] for i in free_idx]
     ]
-    data.constr_lhs = [lhs[:, others] lhs[:, free] -lhs[:, free]]
     data.var_lb = [
-        data.var_lb[others]
-        [0.0 for _ in free]
-        [0.0 for _ in free]
+        [is_var_free[i] ? 0.0 : data.var_lb[i] for i in 1:ncols]
+        [0 for _ in free_idx]
     ]
     data.var_ub = [
-        data.var_ub[others]
-        [Inf for _ in free]
-        [Inf for _ in free]
+        [is_var_free[i] ? Inf : data.var_ub[i] for i in 1:ncols]
+        [Inf for _ in free_idx]
     ]
     data.var_types = [
-        data.var_types[others]
-        data.var_types[free]
-        data.var_types[free]
+        data.var_types
+        [data.var_types[i] for i in free_idx]
     ]
     data.var_names = [
-        data.var_names[others]
-        ["$(v)_p" for v in data.var_names[free]]
-        ["$(v)_m" for v in data.var_names[free]]
+        data.var_names
+        ["$(data.var_names[i])_neg" for i in free_idx]
     ]
+    data.constr_lhs = [lhs -lhs[:, free_idx]]
+    t.is_var_free, t.ncols = is_var_free, ncols
 end
 
 function backwards!(t::SplitFreeVars, c::ConstraintSet)
-    # Convert GE constraints into LE
-    nrows, _ = size(c.lhs)
-    ge = [i for i = 1:nrows if isfinite(c.lb[i])]
-    c.ub[ge], c.lb[ge] = -c.lb[ge], -c.ub[ge]
-    c.lhs[ge, :] *= -1
+    ncols, is_var_free = t.ncols, t.is_var_free
+    free_idx = findall(is_var_free)
 
-    # Assert only LE constraints are left (EQ constraints are not supported)
-    @assert all(c.lb .== -Inf)
-
-    # Combine split free variable coefficients: x = x_p - x_m
-    B, F = t.B, t.F
-    for i = 1:F
-        c.lhs[:, B+i] = c.lhs[:, B+i] - c.lhs[:, B+F+i]
+    for (offset, var_idx) in enumerate(free_idx)
+        @assert c.lhs[:, var_idx] == -c.lhs[:, ncols+offset]
     end
-    c.lhs = c.lhs[:, 1:(B+F)]
+    c.lhs = c.lhs[:, 1:ncols]
 end
 
 function forward(t::SplitFreeVars, p::Vector{Float64})::Vector{Float64}
+    ncols, is_var_free = t.ncols, t.is_var_free
+    free_idx = findall(is_var_free)
     return [
-        p[t.others]
-        max.(p[t.free], 0)
-        max.(-p[t.free], 0)
+        [is_var_free[i] ? max(0, p[i]) : p[i] for i in 1:ncols]
+        [max(0, -p[i]) for i in free_idx]
     ]
 end