Set up multi-formulation architecture; start merging akazachk's code

src/model/formulations/base/structs.jl

@@ -0,0 +1,57 @@
+# UnitCommitment.jl: Optimization Package for Security-Constrained Unit Commitment
+# Copyright (C) 2020, UChicago Argonne, LLC. All rights reserved.
+# Released under the modified BSD license. See COPYING.md for more details.
+
+abstract type _RampingFormulation end
+abstract type _TransmissionFormulation end
+
+struct _GeneratorFormulation
+    ramping::_RampingFormulation
+
+    function _GeneratorFormulation(
+        ramping::_RampingFormulation = _DamKucRajAta16(),
+    )
+        return new(ramping)
+    end
+end
+
+"""
+    mutable struct _ShiftFactorsFormulation <: _TransmissionFormulation
+        isf_cutoff::Float64
+        lodf_cutoff::Float64
+        precomputed_isf::Union{Nothing,Matrix{Float64}}
+        precomputed_lodf::Union{Nothing,Matrix{Float64}}
+    end
+
+Transmission formulation based on Injection Shift Factors (ISF) and Line
+Outage Distribution Factors (LODF). Constraints are enforced in a lazy way.
+
+Arguments
+---------
+- `precomputed_isf::Union{Matrix{Float64},Nothing} = nothing`:
+    the injection shift factors matrix. If not provided, it will be computed.
+- `precomputed_lodf::Union{Matrix{Float64},Nothing} = nothing`: 
+    the line outage distribution factors matrix. If not provided, it will be
+    computed.
+- `isf_cutoff::Float64 = 0.005`: 
+    the cutoff that should be applied to the ISF matrix. Entries with magnitude
+    smaller than this value will be set to zero.
+- `lodf_cutoff::Float64 = 0.001`: 
+    the cutoff that should be applied to the LODF matrix. Entries with magnitude
+    smaller than this value will be set to zero.
+"""
+mutable struct _ShiftFactorsFormulation <: _TransmissionFormulation
+    isf_cutoff::Float64
+    lodf_cutoff::Float64
+    precomputed_isf::Union{Nothing,Matrix{Float64}}
+    precomputed_lodf::Union{Nothing,Matrix{Float64}}
+
+    function _ShiftFactorsFormulation(;
+        isf_cutoff = 0.005,
+        lodf_cutoff = 0.001,
+        precomputed_isf = nothing,
+        precomputed_lodf = nothing,
+    )
+        return new(isf_cutoff, lodf_cutoff, precomputed_isf, precomputed_lodf)
+    end
+end