From 1bf18fe8e10a495d845acf1d6da468a20987ad1e Mon Sep 17 00:00:00 2001
From: Jeremy Saklad <saklad5@me.com>
Date: Tue, 28 Sep 2021 17:05:06 -0500
Subject: [PATCH] Add BoneMarketModel.AddDivisionMultiplicationEquality

This method combines two common operations, avoiding the need for
intermediate variables at the call site.
---
 bonemarketsolver/objects/bone_market_model.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/bonemarketsolver/objects/bone_market_model.py b/bonemarketsolver/objects/bone_market_model.py
index ff62701..a39a0b5 100644
--- a/bonemarketsolver/objects/bone_market_model.py
+++ b/bonemarketsolver/objects/bone_market_model.py
@@ -33,6 +33,24 @@ Each parameter is interpreted as a BoundedLinearExpression, and a layer of indir
         super().AddDivisionEquality(intermediate_target, intermediate_num, intermediate_denom)
         return (target_constraint, num_constraint, denom_constraint)
 
+    def AddDivisionMultiplicationEquality(self, target, num, denom, multiple = None):
+        """Adds `target == (num // denom) * multiple`.
+
+Each parameter is interpreted as a BoundedLinearExpression, and a layer of indirection is applied such that each Constraint in the returned tuple can accept an enforcement literal.
+
+`multiple` defaults to the same value as `denom` if unspecified."""
+        quotient = self.NewIntVar(f'{repr(target)} == ({repr(num)} // {repr(denom)}) * {repr(multiple)}: quotient')
+        intermediate_num, num_constraint = self.NewIntermediateIntVar(num, f'{repr(target)} == ({repr(num)} // {repr(denom)}) * {repr(multiple)}: num', lb = 0)
+        intermediate_denom, denom_constraint = self.NewIntermediateIntVar(denom, f'{repr(target)} == ({repr(num)} // {repr(denom)}) * {repr(multiple)}: denom', lb = 0)
+        intermediate_target, target_constraint = self.NewIntermediateIntVar(target, f'{repr(target)} == ({repr(num)} // {repr(denom)}) * {repr(multiple)}: target')
+        if multiple:
+            intermediate_multiple, multiple_constraint = self.NewIntermediateIntVar(multiple, f'{repr(target)} == ({repr(num)} // {repr(denom)}) * {repr(multiple)}: multiple')
+
+        super().AddDivisionEquality(quotient, intermediate_num, intermediate_denom)
+        super().AddMultiplicationEquality(intermediate_target, (quotient, intermediate_multiple if multiple else intermediate_denom))
+
+        return (num_constraint, denom_constraint, target_constraint, *((multiple_constraint,) if multiple else ()))
+
     def AddIf(self, variable, *constraints):
         """Add constraints to the model, only enforced if the specified variable is true.