adds right and above juxtaposition functionality and unit tests

permuta/perm_sets/permset.py

@@ -1,6 +1,6 @@
 import multiprocessing
-from itertools import islice
-from typing import ClassVar, Dict, Iterable, List, NamedTuple, Optional, Union
+from itertools import combinations, islice
+from typing import ClassVar, Dict, Iterable, Iterator, List, NamedTuple, Optional, Union
 
 from ..patterns import MeshPatt, Perm
 from ..permutils import is_finite, is_insertion_encodable, is_polynomial
@@ -202,6 +202,132 @@ def _all(self) -> Iterable[Perm]:
             yield from gen
             length += 1
 
+    def right_juxtaposition(self, other: "Av") -> "Av":
+        """Compute the basis of the juxtaposition of two permutation classes.
+
+        Given self = Av(B1) and other = Av(B2), returns the permutation class
+        E = Av(B) where E consists of all permutations that can be written as
+        the juxtaposition of a permutation from self on the left and a
+        permutation from other on the right.
+
+        Raises NotImplementedError: If either basis is a MeshBasis.
+        """
+        if not isinstance(self.basis, Basis) or not isinstance(other.basis, Basis):
+            raise NotImplementedError(Av._BASIS_ONLY_MSG)
+
+        candidates: List[Perm] = []
+
+        for b1 in self.basis:
+            for b2 in other.basis:
+                # |σ| = 0 case: no overlap
+                candidates.extend(self._sigma_0_candidates(b1, b2))
+                # |σ| = 1 case: one element overlap
+                candidates.extend(self._sigma_1_candidates(b1, b2))
+
+        # Basis constructor automatically minimizes
+        return Av(Basis(*candidates))
+
+    def above_juxtaposition(self, other: "Av") -> "Av":
+        """Compute the basis of the above juxtaposition of two permutation classes.
+
+        Given self = Av(B1) and other = Av(B2), returns the permutation class
+        where self is on the bottom and other is on top.
+
+        This is computed by taking inverses, computing right_juxtaposition,
+        then inverting the result.
+
+        Raises NotImplementedError: If either basis is a MeshBasis.
+        """
+        if not isinstance(self.basis, Basis) or not isinstance(other.basis, Basis):
+            raise NotImplementedError(Av._BASIS_ONLY_MSG)
+
+        # Compute inverse classes
+        self_inverse = Av(Basis(*[p.inverse() for p in self.basis]))
+        other_inverse = Av(Basis(*[p.inverse() for p in other.basis]))
+
+        # Compute right juxtaposition of inverses
+        result_inverse = self_inverse.right_juxtaposition(other_inverse)
+
+        # Return inverse of result
+        return Av(Basis(*[p.inverse() for p in result_inverse.basis]))
+
+    @staticmethod
+    def _sigma_0_candidates(b1: Perm, b2: Perm) -> Iterator[Perm]:
+        """Generate candidates where left and right patterns don't overlap.
+
+        Generates all permutations of length |b1| + |b2| where the first |b1|
+        positions have pattern b1 and the last |b2| positions have pattern b2.
+        """
+        n1, n2 = len(b1), len(b2)
+        total = n1 + n2
+
+        # Choose which values go to the left block
+        for left_values in combinations(range(total), n1):
+            right_values = [v for v in range(total) if v not in left_values]
+
+            # Build the permutation
+            result = [0] * total
+            # Left positions get values according to pattern b1
+            for pos in range(n1):
+                result[pos] = left_values[b1[pos]]
+            # Right positions get values according to pattern b2
+            for pos in range(n2):
+                result[n1 + pos] = right_values[b2[pos]]
+
+            yield Perm(result)
+
+    @staticmethod
+    def _sigma_1_candidates(  # pylint: disable=R0914
+        b1: Perm, b2: Perm
+    ) -> Iterator[Perm]:
+        """Generate candidates where left and right patterns overlap by one element.
+
+        Generates all permutations of length |b1| + |b2| - 1 where the first |b1|
+        positions have pattern b1 and the last |b2| positions have pattern b2,
+        with position |b1| - 1 shared between both patterns.
+        """
+        n1, n2 = len(b1), len(b2)
+        total = n1 + n2 - 1
+
+        # The shared position is at index n1 - 1
+        # Its value v must satisfy: v = b1[-1] + b2[0]
+        # (it must be at rank b1[-1] among left and rank b2[0] among right values)
+        v = b1[-1] + b2[0]
+
+        # Values less than v: {0, ..., v-1}
+        # Values greater than v: {v+1, ..., total-1}
+        values_below = list(range(v))
+        values_above = list(range(v + 1, total))
+
+        # Left block needs b1[-1] values below v, right block gets the rest
+        k1 = b1[-1]  # number of values < v in left block
+
+        # Iterate over all ways to partition values below v
+        for left_below in combinations(values_below, k1):
+            right_below = [x for x in values_below if x not in left_below]
+
+            # Iterate over all ways to partition values above v
+            for left_above in combinations(values_above, n1 - 1 - k1):
+                right_above = [x for x in values_above if x not in left_above]
+
+                # Build the left and right value sets
+                left_values = sorted(list(left_below) + [v] + list(left_above))
+                right_values = sorted(right_below + [v] + right_above)
+
+                # Build the permutation
+                result = [0] * total
+
+                # Left positions (0 to n1-1) get values according to pattern b1
+                for pos in range(n1):
+                    result[pos] = left_values[b1[pos]]
+
+                # Right positions (n1-1 to total-1) get values according to pattern b2
+                # But position n1-1 is already set, so we only set n1 to total-1
+                for pos in range(1, n2):
+                    result[n1 - 1 + pos] = right_values[b2[pos]]
+
+                yield Perm(result)
+
     def __str__(self) -> str:
         return f"Av({','.join(str(p) for p in self.basis)})"
 

tests/perm_sets/test_av.py

@@ -291,3 +291,160 @@ def test_invalid_ops_with_mesh_patt():
         Av(MeshBasis(Perm((0, 1)))).is_insertion_encodable()
     with pytest.raises(NotImplementedError):
         Av(MeshBasis(Perm((0, 1)))).is_polynomial()
+
+
+# Tests for right_juxtaposition
+
+
+def test_right_juxtaposition_basic():
+    """Test Av(21) | Av(12) = Av(213, 312)."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_12 = Av(Basis(Perm((0, 1))))
+    result = av_21.right_juxtaposition(av_12)
+    expected_basis = {Perm((1, 0, 2)), Perm((2, 0, 1))}
+    assert set(result.basis) == expected_basis
+
+
+def test_right_juxtaposition_same_class():
+    """Test Av(21) | Av(21) gives expected basis."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    result = av_21.right_juxtaposition(av_21)
+    # Basis should be {321, 2143, 2431} = {(2,1,0), (1,0,3,2), (1,3,2,0)}
+    expected_basis = {Perm((2, 1, 0)), Perm((1, 0, 3, 2)), Perm((2, 0, 3, 1))}
+    assert set(result.basis) == expected_basis
+
+
+def test_right_juxtaposition_enumeration():
+    """Test that juxtaposition class has correct enumeration."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_12 = Av(Basis(Perm((0, 1))))
+    result = av_21.right_juxtaposition(av_12)
+    # [Av(21)|Av(12)] = permutations that can be split into decreasing|increasing
+    # Enumeration: 1, 1, 2, 4, 8, 16, 32 (powers of 2 starting at n=2)
+    assert result.enumeration(6) == [1, 1, 2, 4, 8, 16, 32]
+
+
+def test_right_juxtaposition_multiple_basis_elements():
+    """Test juxtaposition with multiple basis elements."""
+    # Only contains empty and singleton permutations
+    av_21_12 = Av(Basis(Perm((1, 0)), Perm((0, 1))))
+    av_132 = Av(Basis(Perm((0, 2, 1))))
+    result = av_21_12.right_juxtaposition(av_132)
+    # The result should be a valid Av object with a minimized basis
+    assert isinstance(result.basis, Basis)
+    assert len(result.basis) > 0
+
+
+def test_right_juxtaposition_longer_patterns():
+    """Test juxtaposition with longer patterns."""
+    av_132 = Av(Basis(Perm((0, 2, 1))))
+    av_231 = Av(Basis(Perm((1, 2, 0))))
+    result = av_132.right_juxtaposition(av_231)
+    # Verify result is valid and has expected structure
+    assert isinstance(result.basis, Basis)
+    # All basis elements should have length between 3 and 6 (|b1|+|b2|-1 to |b1|+|b2|)
+    for perm in result.basis:
+        assert 5 <= len(perm) <= 6
+
+
+def test_right_juxtaposition_mesh_basis_raises():
+    """Test that juxtaposition with MeshBasis raises NotImplementedError."""
+    av_classical = Av(Basis(Perm((1, 0))))
+    av_mesh = Av(MeshBasis(Perm((0, 1))))
+    with pytest.raises(NotImplementedError):
+        av_classical.right_juxtaposition(av_mesh)
+    with pytest.raises(NotImplementedError):
+        av_mesh.right_juxtaposition(av_classical)
+
+
+def test_right_juxtaposition_containment():
+    """Test that permutations in the juxtaposition class can be split correctly."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_12 = Av(Basis(Perm((0, 1))))
+    result = av_21.right_juxtaposition(av_12)
+
+    # Check some permutations that should be in the class
+    # 21 can be split as (2)|(1) where (2) is decreasing and (1) is increasing
+    assert Perm((1, 0)) in result
+    # 12 can be split as ()|(12) where () is trivially decreasing and (12) is increasing
+    assert Perm((0, 1)) in result
+    # 1 is trivially in the class
+    assert Perm((0,)) in result
+
+    # Check some permutations that should NOT be in the class
+    # 213 = (1,0,2) is a basis element, so not in the class
+    assert Perm((1, 0, 2)) not in result
+    # 312 = (2,0,1) is a basis element, so not in the class
+    assert Perm((2, 0, 1)) not in result
+
+
+# Tests for above_juxtaposition
+
+
+def test_above_juxtaposition_basic():
+    """Test basic above juxtaposition with Av(21) below and Av(12) above."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_12 = Av(Basis(Perm((0, 1))))
+    result = av_21.above_juxtaposition(av_12)
+    # Result should be valid Av with Basis
+    assert isinstance(result.basis, Basis)
+    assert len(result.basis) > 0
+
+
+def test_above_juxtaposition_inverse_relationship():
+    """Test that above_juxtaposition relates to right_juxtaposition via inverses."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_132 = Av(Basis(Perm((0, 2, 1))))
+
+    # Compute above juxtaposition directly
+    above_result = av_21.above_juxtaposition(av_132)
+
+    # Compute via inverses manually
+    av_21_inv = Av(Basis(*[p.inverse() for p in av_21.basis]))
+    av_132_inv = Av(Basis(*[p.inverse() for p in av_132.basis]))
+    right_result = av_21_inv.right_juxtaposition(av_132_inv)
+    manual_result = Av(Basis(*[p.inverse() for p in right_result.basis]))
+
+    # The bases should be equivalent
+    assert set(above_result.basis) == set(manual_result.basis)
+
+
+def test_above_juxtaposition_enumeration():
+    """Test that above juxtaposition class has expected enumeration."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    av_12 = Av(Basis(Perm((0, 1))))
+    result = av_21.above_juxtaposition(av_12)
+    # Permutations that can be split by value: lower values decreasing, upper increasing
+    # This should give 2^(n-1) for n >= 1
+    assert result.enumeration(6) == [1, 1, 2, 4, 8, 16, 32]
+
+
+def test_above_juxtaposition_same_class():
+    """Test above juxtaposition with the same class."""
+    av_21 = Av(Basis(Perm((1, 0))))
+    result = av_21.above_juxtaposition(av_21)
+    # Should be valid and have a non-empty basis
+    assert isinstance(result.basis, Basis)
+    assert len(result.basis) > 0
+
+
+def test_above_juxtaposition_longer_patterns():
+    """Test above juxtaposition with longer patterns."""
+    av_132 = Av(Basis(Perm((0, 2, 1))))
+    av_231 = Av(Basis(Perm((1, 2, 0))))
+    result = av_132.above_juxtaposition(av_231)
+    # Verify result is valid
+    assert isinstance(result.basis, Basis)
+    # All basis elements should have length between 5 and 6
+    for perm in result.basis:
+        assert 5 <= len(perm) <= 6
+
+
+def test_above_juxtaposition_mesh_basis_raises():
+    """Test that above_juxtaposition with MeshBasis raises NotImplementedError."""
+    av_classical = Av(Basis(Perm((1, 0))))
+    av_mesh = Av(MeshBasis(Perm((0, 1))))
+    with pytest.raises(NotImplementedError):
+        av_classical.above_juxtaposition(av_mesh)
+    with pytest.raises(NotImplementedError):
+        av_mesh.above_juxtaposition(av_classical)