Fix bug in MonomialIndex.__lt__

1 files changed, 11 insertions, 5 deletions

diff --git a/polymatrix/polymatrix/index.py b/polymatrix/polymatrix/index.py
index c68e23f..fd2a759 100644
--- a/polymatrix/polymatrix/index.py
+++ b/polymatrix/polymatrix/index.py
@@ -74,10 +74,16 @@ class MonomialIndex(tuple[VariableIndex]):
         # they have the same degree the index counts
         if self.degree == other.degree:
             # Assumes that monomialindex is sorted!
-            # if the first variable is also the same continue until one
-            # finishes or the values differ.
-            # FIXME: check that return value is not none
-            s, o = next(dropwhile(lambda t: t[0] == t[1], zip(self, other)))
+            def expand(m):
+                for v in m:
+                    for _ in range(v.power):
+                        yield v
+
+            def same_index(t):
+                s, o = t
+                return s.index == o.index
+        
+            s, o = next(dropwhile(same_index, zip(expand(self), expand(other))))
             return s < o
 
         return self.degree < other.degree
@@ -231,7 +237,7 @@ class PolyDict(UserDict[MonomialIndex, int | float]):
         p = PolyDict.empty()
 
         for (lm, lv), (rm, rv) in product(left.items(), right.items()):
-            pv = lv + rv
+            pv = lv * rv
 
             if math.isclose(pv, 0):
                 continue