Classify RationalFunction2 degrees in descending coefficient order

blueprint/src/python/functions.py

@@ -686,7 +686,7 @@ def __repr__(self):
         if self.is_zero():
             return f"0 on {self.domain}"
         if self.is_constant():
-            return f"{self._num_coeffs[0] / self._den_coeffs[0]} on {self.domain}"
+            return f"{self._num_coeffs[-1] / self._den_coeffs[-1]} on {self.domain}"
 
         num = RationalFunction2._poly_str(self._num_coeffs, "x")
         den = RationalFunction2._poly_str(self._den_coeffs, "x")
@@ -732,12 +732,12 @@ def is_zero(self):
         return all(c == 0 for c in self._num_coeffs)
 
     def is_constant(self):
-        return all(c == 0 for c in self._num_coeffs[1:]) and \
-                all(c == 0 for c in self._den_coeffs[1:])
+        return all(c == 0 for c in self._num_coeffs[:-1]) and \
+                all(c == 0 for c in self._den_coeffs[:-1])
 
     def is_affine(self):
-        return all(c == 0 for c in self._num_coeffs[2:]) and \
-                all(c == 0 for c in self._den_coeffs[1:])
+        return all(c == 0 for c in self._num_coeffs[:-2]) and \
+                all(c == 0 for c in self._den_coeffs[:-1])
 
 
 # Represents the univariate function P(x)/Q(x) where P, Q are polynomials. Currently

blueprint/src/python/tests/test_function_degree_regression.py

@@ -0,0 +1,28 @@
+from functions import Interval, RationalFunction2
+
+
+def function(numerator, denominator=(1,)):
+    return RationalFunction2((list(numerator), list(denominator)), Interval(0, 1))
+
+
+def test_monomials_have_their_actual_degree():
+    linear = function((1, 0))
+    quadratic = function((1, 0, 0))
+    assert not linear.is_constant()
+    assert linear.is_affine()
+    assert not quadratic.is_constant()
+    assert not quadratic.is_affine()
+
+
+def test_leading_zeros_do_not_raise_degree():
+    constant = function((0, 0, 2), (0, 1))
+    assert constant.is_constant()
+    assert constant.is_affine()
+    assert str(constant) == "2.0 on [0,1)"
+    assert function((0, 1, 2)).is_affine()
+
+
+def test_nonconstant_denominator_is_not_affine():
+    reciprocal = function((1,), (1, 0))
+    assert not reciprocal.is_constant()
+    assert not reciprocal.is_affine()