Default PEPS gates to reduce split

Author: rezaquant

src/pepsy/operators/gates.py

@@ -1633,8 +1633,10 @@ def gate(tn, gates, where=None, which=None, **kwargs):
     when ``contract`` is ``"split"`` or ``"reduce-split"``. For other contract
     modes, the gate is applied directly to the requested endpoints.
     By default, 2D/3D routing uses ``sequence="auto"`` to choose a shortest
-    route with the smallest current virtual-bond bottleneck. Pass an explicit
-    deterministic sequence to force a particular route.
+    route with the smallest current virtual-bond bottleneck, and
+    ``contract="reduce-split"`` for quimb's reduced two-site split path. Pass
+    an explicit deterministic sequence or contract mode to force a particular
+    route or split strategy.
     The efficient routed pattern is::
 
         gate(
@@ -1730,7 +1732,7 @@ def gate(tn, gates, where=None, which=None, **kwargs):
 
         if arity == 2:
             opts_local = dict(opts)
-            opts_local.setdefault("contract", "split")
+            opts_local.setdefault("contract", "reduce-split")
             if which_payload is not None:
                 opts_local["ind_id"] = _ind_id_from_which(which_payload, 2)
             elif (which_default is not None) and ("ind_id" not in opts_local):
@@ -1748,7 +1750,7 @@ def gate(tn, gates, where=None, which=None, **kwargs):
 
         if arity == 3:
             opts_local = dict(opts)
-            opts_local.setdefault("contract", "split")
+            opts_local.setdefault("contract", "reduce-split")
             if which_payload is not None:
                 opts_local["ind_id"] = _ind_id_from_which(which_payload, 3)
             elif (which_default is not None) and ("ind_id" not in opts_local):
@@ -2203,7 +2205,7 @@ def _apply_gate_2d(
     bond_dim=None,
     max_bond=None,
     bra=False,
-    contract="split",
+    contract="reduce-split",
     tags=None,
     dtype="complex128",
     cutoff=1.0e-12,
@@ -2478,7 +2480,7 @@ def _apply_gate_3d(
     bond_dim=None,
     max_bond=None,
     bra=False,
-    contract="split",
+    contract="reduce-split",
     tags=None,
     dtype="complex128",
     cutoff=1.0e-12,
@@ -2692,7 +2694,7 @@ def build_pepo_from_gates(
     dtype="complex128",
     max_bond=16,
     sequence="auto",
-    contract="split",
+    contract="reduce-split",
     ind_id="k{},{}",
 ):
     """Build a PEPO from gate-style input on top of a PEPO identity.
@@ -2725,8 +2727,9 @@ def build_pepo_from_gates(
         2D SWAP-path preference for long-range two-site gates. Defaults to
         ``"auto"`` for the same lower-bond smart routing used by
         :func:`gate`.
-    contract : str, default="split"
-        Gate contraction mode.
+    contract : str, default="reduce-split"
+        Gate contraction mode. The default uses quimb's reduced two-site split
+        path, which is usually cheaper than ``"split"`` for PEPO/PEPS tensors.
     ind_id : str, default="k{},{}"
         Physical index format used for PEPO ket-family indices.
 
@@ -2806,7 +2809,7 @@ def build_mpo_from_gates(
     mpo_=None,
     dtype="complex128",
     max_bond=16,
-    contract="split",
+    contract="reduce-split",
     ind_id="k{}",
 ):
     """Build an MPO from gate-style input on top of an MPO identity.
@@ -2835,8 +2838,9 @@ def build_mpo_from_gates(
     max_bond : int, default=16
         Per-gate local split truncation cap and fallback construction
         compression cap.
-    contract : str, default="split"
-        Gate contraction mode.
+    contract : str, default="reduce-split"
+        Gate contraction mode. The default uses quimb's reduced two-site split
+        path, which is usually cheaper than ``"split"`` for MPO tensors.
     ind_id : str, default="k{}"
         Physical index format used for MPO ket-family indices.
 

src/pepsy/tensors/symmetric.py

@@ -689,7 +689,7 @@ def apply_gates(
         self,
         gates,
         *,
-        contract="split",
+        contract="auto",
         max_bond=None,
         cutoff=1e-10,
         normalize=False,
@@ -702,6 +702,7 @@ def apply_gates(
         """Apply a bundled local gate stream to this state."""
         target = self if inplace else self.copy()
         method = str(method).strip().lower()
+        contract_auto = contract is None or str(contract).strip().lower() == "auto"
         if max_bond is not None:
             compress_opts.setdefault("max_bond", max_bond)
         if cutoff is not None:
@@ -711,7 +712,8 @@ def apply_gates(
             from ..operators import gate as pepsy_gate
 
             opts = dict(compress_opts)
-            opts.setdefault("contract", contract)
+            if not contract_auto:
+                opts.setdefault("contract", contract)
             opts.update({} if gate_kwargs is None else dict(gate_kwargs))
             target.network = pepsy_gate(
                 target.network,
@@ -752,7 +754,7 @@ def apply_gates(
                 target.network,
                 gate,
                 inds,
-                contract=contract,
+                contract="split" if contract_auto else contract,
                 tags=[],
                 info=None,
                 inplace=True,
@@ -775,7 +777,7 @@ def time_evolve(
         max_bond=None,
         cutoff=1e-10,
         normalize=None,
-        contract="split",
+        contract="auto",
         inplace=True,
         method="direct",
         gauges=None,

tests/test_gate.py

@@ -611,6 +611,38 @@ def _fake_bulk_helper(tn_i, G_arg, where=None, **kwargs):
         assert has_inplace_kw is (dim == "1d")
 
 
+def test_gate_2d_3d_default_contract_is_reduce_split(monkeypatch):
+    """PEPS-like direct gate routing should default to quimb's reduce-split."""
+    calls = []
+
+    def _fake_gate_2d(tn, G_arg, where=None, **kwargs):
+        calls.append(("2d", where, kwargs.get("contract")))
+        return tn
+
+    def _fake_gate_3d(tn, G_arg, where=None, **kwargs):
+        calls.append(("3d", where, kwargs.get("contract")))
+        return tn
+
+    monkeypatch.setattr("pepsy.operators.gates._apply_gate_2d", _fake_gate_2d)
+    monkeypatch.setattr("pepsy.operators.gates._apply_gate_3d", _fake_gate_3d)
+
+    class _Dummy3DTN:  # pylint: disable=too-few-public-methods
+        Lx = 1
+        Ly = 1
+        Lz = 2
+
+    gate_op = np.eye(4, dtype=np.complex128).reshape(2, 2, 2, 2)
+    peps = ps_to_peps(1, 2, dtype="complex128")
+    tn3d = _Dummy3DTN()
+
+    assert apply_gate(peps, gate_op, ((0, 0), (0, 1))) is peps
+    assert apply_gate(tn3d, gate_op, ((0, 0, 0), (0, 0, 1))) is tn3d
+    assert calls == [
+        ("2d", ((0, 0), (0, 1)), "reduce-split"),
+        ("3d", ((0, 0, 0), (0, 0, 1)), "reduce-split"),
+    ]
+
+
 @pytest.mark.parametrize("dim", ("1d", "2d", "3d"))
 def test_gate_sequence_dispatch_inplace_false_copies(monkeypatch, dim):
     """Bundled streams should copy TN first when ``inplace=False``."""
@@ -1071,6 +1103,7 @@ def _fake_gate(tn, gate, where, **kwargs):
     where, kwargs = calls[0]
     assert where == (0, 2)
     assert kwargs["max_bond"] == 5
+    assert kwargs["contract"] == "reduce-split"
     assert "bond_dim" not in kwargs
     assert kwargs["ind_id"] == "k{}"
 
@@ -1123,6 +1156,7 @@ def _fake_gate(tn, gate, where, **kwargs):
     where, kwargs = calls[0]
     assert where == ((0, 0), (1, 2))
     assert kwargs["max_bond"] == 6
+    assert kwargs["contract"] == "reduce-split"
     assert "bond_dim" not in kwargs
     assert kwargs["sequence"] == "auto"
     assert kwargs["ind_id"] == "k{},{}"

tests/test_symmetric_tensors.py

@@ -388,6 +388,33 @@ def test_sympeps_gate_stream_runs_pepsy_gate_and_gate_simple():
     assert np.isfinite(np.real(out_simple.norm()))
 
 
+def test_sympeps_gate_method_preserves_pepsy_gate_contract_default(monkeypatch):
+    """SymPEPS method='gate' should not override pepsy.gate's default."""
+    state = SymPEPS.for_model(
+        "heisenberg",
+        2,
+        2,
+        bond_dim=2,
+        seed=12,
+        dtype="complex128",
+    )
+    calls = []
+
+    def _fake_gate(tn, gates, **kwargs):
+        calls.append((gates, kwargs.copy()))
+        return tn
+
+    monkeypatch.setattr("pepsy.operators.gate", _fake_gate)
+
+    out = state.copy().apply_gates(
+        ((np.eye(2, dtype=np.complex128), ((0, 0),)),),
+        method="gate",
+    )
+
+    assert out.tn is not None
+    assert "contract" not in calls[0][1]
+
+
 def test_sympeps_raw_pepsy_gate_functions_accept_symmray_streams():
     """The plain gate functions should accept a SymGateStream directly."""
     state = SymPEPS.for_model("itf", 2, 2, bond_dim=2, seed=10, dtype="complex128")