Update models.md

docs/src/manual/models.md

@@ -439,6 +439,72 @@ optimize!(model)
 reduced_cost(x)  # Works
 ```
 
+## Get the matrix representation
+
+Use [`lp_matrix_data`](@ref) to return a data structure that represents the
+matrix form of a linear program.
+
+```jldoctest
+julia> begin
+           model = Model()
+           @variable(model, x >= 1)
+           @variable(model, 2 <= y)
+           @variable(model, 3 <= z <= 4)
+           @constraint(model, x == 5)
+           @constraint(model, 2x + 3y <= 6)
+           @constraint(model, -4y >= 5z + 7)
+           @constraint(model, -1 <= x + y <= 2)
+           @objective(model, Max, 1 + 2x)
+       end;
+
+julia> data = lp_matrix_data(model);
+
+julia> data.A
+4×3 SparseArrays.SparseMatrixCSC{Float64, Int64} with 7 stored entries:
+ 1.0    ⋅     ⋅ 
+  ⋅   -4.0  -5.0
+ 2.0   3.0    ⋅ 
+ 1.0   1.0    ⋅ 
+
+julia> data.b_lower
+4-element Vector{Float64}:
+   5.0
+   7.0
+ -Inf
+  -1.0
+
+julia> data.b_upper
+4-element Vector{Float64}:
+  5.0
+ Inf
+  6.0
+  2.0
+
+julia> data.x_lower
+3-element Vector{Float64}:
+ 1.0
+ 2.0
+ 3.0
+
+julia> data.x_upper
+3-element Vector{Float64}:
+ Inf
+ Inf
+  4.0
+
+julia> data.c
+3-element Vector{Float64}:
+ 2.0
+ 0.0
+ 0.0
+
+julia> data.c_offset
+1.0
+
+julia> data.sense
+MAX_SENSE::OptimizationSense = 1
+```
+
 ## Backends
 
 !!! info