1 files changed, 70 insertions, 0 deletions
diff --git a/polymatrix/expression/mixins/additionexprmixin.py b/polymatrix/expression/mixins/additionexprmixin.py
new file mode 100644
index 0000000..776e952
--- /dev/null
+++ b/polymatrix/expression/mixins/additionexprmixin.py
@@ -0,0 +1,70 @@
+
+import abc
+import typing
+import dataclass_abc
+
+from polymatrix.expression.init.initpolymatrix import init_poly_matrix
+from polymatrix.expression.mixins.expressionbasemixin import ExpressionBaseMixin
+from polymatrix.expression.polymatrix import PolyMatrix
+from polymatrix.polymatrixexprstate import PolyMatrixExprState
+
+
+class AddExprMixin(ExpressionBaseMixin):
+    @property
+    @abc.abstractmethod
+    def left(self) -> ExpressionBaseMixin:
+        ...
+
+    @property
+    @abc.abstractmethod
+    def right(self) -> ExpressionBaseMixin:
+        ...
+
+    # overwrites abstract method of `ExpressionBaseMixin`
+    @property
+    def shape(self) -> tuple[int, int]:
+        return self.left.shape
+
+    # overwrites abstract method of `ExpressionBaseMixin`
+    def apply(
+        self, 
+        state: PolyMatrixExprState,
+    ) -> tuple[PolyMatrixExprState, PolyMatrix]:
+        state, left = self.left.apply(state=state)
+        state, right = self.right.apply(state=state)
+
+        assert left.shape == right.shape
+
+        terms = {}
+
+        for underlying in (left, right):
+
+            for row in range(self.shape[0]):
+                for col in range(self.shape[1]):
+                    
+                    if (row, col) in terms:
+                        terms_row_col = terms[row, col]
+
+                    else:
+                        terms_row_col = {}
+
+                    try:
+                        underlying_terms = underlying.get_poly(row, col)
+                    except KeyError:
+                        continue
+
+                    for monomial, value in underlying_terms.items():
+                        
+                        if monomial not in terms_row_col:
+                            terms_row_col[monomial] = 0
+
+                        terms_row_col[monomial] += value
+
+                    terms[row, col] = terms_row_col
+
+        poly_matrix = init_poly_matrix(
+            terms=terms,
+            shape=self.shape,
+        )
+
+        return state, poly_matrix