bug fix: monomial returned by subtract_monomial cannot have negative powers

5 files changed, 22 insertions, 10 deletions

diff --git a/polymatrix/expression/init/initevalexpr.py b/polymatrix/expression/init/initevalexpr.py
index dad9664..5bbd404 100644
--- a/polymatrix/expression/init/initevalexpr.py
+++ b/polymatrix/expression/init/initevalexpr.py
@@ -41,15 +41,15 @@ def init_eval_expr(
 					yield from value[variable]
 
 			elif isinstance(value, int) or isinstance(value, float):
-				# else:
 				yield value
 
 			else:
 				yield float(value)
-				# raise Exception(f'{value=}, {type(value)=}')
+
+	values = tuple(gen_formatted_values())
 
 	return EvalExprImpl(
 		underlying=underlying,
 		variables=variables,
-		values=tuple(gen_formatted_values()),
+		values=values,
 )
diff --git a/polymatrix/expression/mixins/subtractmonomialsexprmixin.py b/polymatrix/expression/mixins/subtractmonomialsexprmixin.py
index b55f412..d5091c6 100644
--- a/polymatrix/expression/mixins/subtractmonomialsexprmixin.py
+++ b/polymatrix/expression/mixins/subtractmonomialsexprmixin.py
@@ -8,7 +8,7 @@ from polymatrix.expressionstate.mixins.expressionstatemixin import ExpressionSta
 from polymatrix.polymatrix.mixins.polymatrixmixin import PolyMatrixMixin
 from polymatrix.expression.utils.getmonomialindices import get_monomial_indices
 from polymatrix.expression.utils.sortmonomials import sort_monomials
-from polymatrix.expression.utils.subtractmonomialindices import subtract_monomial_indices
+from polymatrix.expression.utils.subtractmonomialindices import SubtractError, subtract_monomial_indices
 
 
 class SubtractMonomialsExprMixin(ExpressionBaseMixin):
@@ -36,7 +36,7 @@ class SubtractMonomialsExprMixin(ExpressionBaseMixin):
                 for m2 in sub_monomials:
                     try:
                         remainder = subtract_monomial_indices(m1, m2)
-                    except KeyError:
+                    except SubtractError:
                         continue
 
                     yield remainder
diff --git a/polymatrix/expression/utils/getvariableindices.py b/polymatrix/expression/utils/getvariableindices.py
index c72bb02..7010d23 100644
--- a/polymatrix/expression/utils/getvariableindices.py
+++ b/polymatrix/expression/utils/getvariableindices.py
@@ -33,6 +33,6 @@ def get_variable_indices(state, variables):
                 yield variable
 
             else:
-                state.offset_dict[variable][0]
+                yield state.offset_dict[variable][0]
 
     return state, tuple(gen_indices())
diff --git a/polymatrix/expression/utils/subtractmonomialindices.py b/polymatrix/expression/utils/subtractmonomialindices.py
index 766997a..236ba9c 100644
--- a/polymatrix/expression/utils/subtractmonomialindices.py
+++ b/polymatrix/expression/utils/subtractmonomialindices.py
@@ -1,13 +1,23 @@
 from polymatrix.expression.utils.sortmonomialindices import sort_monomial_indices
 
 
+class SubtractError(Exception):
+    pass
+
+
 def subtract_monomial_indices(m1, m2):
     m1_dict = dict(m1)
 
     for index, count in m2:
+        if index not in m1_dict:
+            raise SubtractError()
+
         m1_dict[index] -= count
 
         if m1_dict[index] == 0:
             del m1_dict[index]
 
+        elif m1_dict[index] < 0:
+            raise SubtractError()
+
     return sort_monomial_indices(m1_dict.items())
diff --git a/polymatrix/expressionstate/mixins/expressionstatemixin.py b/polymatrix/expressionstate/mixins/expressionstatemixin.py
index 523d2b7..6d2ded3 100644
--- a/polymatrix/expressionstate/mixins/expressionstatemixin.py
+++ b/polymatrix/expressionstate/mixins/expressionstatemixin.py
@@ -31,10 +31,12 @@ class ExpressionStateMixin(
     def auxillary_equations(self) -> dict[int, dict[tuple[int], float]]:
         ...
 
-    # @property
-    # @abc.abstractmethod
-    # def cache(self) -> dict:
-    #     ...
+    def get_variable_from_offset(self, offset: int):
+        for variable, (start, end) in self.offset_dict.items():
+            if offset == start:
+                assert end - start == 1, f'{start=}, {end=}, {variable=}'
+
+                return variable
 
     def register(
         self,