Remove the constraint that stim.Tableau.from_state_vector inputs must be normalized

src/stim/stabilizers/tableau.pybind.cc

@@ -2130,8 +2130,16 @@ void stim_pybind::pybind_tableau_methods(pybind11::module &m, pybind11::class_<T
             }
 
             std::vector<std::complex<float>> v;
+            double weight = 0;
             for (const auto &obj : state_vector) {
                 v.push_back(pybind11::cast<std::complex<float>>(obj));
+                weight += std::norm(v.back());
+            }
+            if (weight != 1.0 && weight > 0.0) {
+                std::complex<float> scale = (float)sqrt(1.0 / weight);
+                for (auto &amplitude : v) {
+                    amplitude *= scale;
+                }
             }
 
             return circuit_to_tableau<MAX_BITWORD_WIDTH>(
@@ -2147,7 +2155,7 @@ void stim_pybind::pybind_tableau_methods(pybind11::module &m, pybind11::class_<T
             Args:
                 state_vector: A list of complex amplitudes specifying a superposition. The
                     vector must correspond to a state that is reachable using Clifford
-                    operations, and must be normalized (i.e. it must be a unit vector).
+                    operations.
                 endian:
                     "little": state vector is in little endian order, where higher index
                         qubits correspond to larger changes in the state index.

src/stim/stabilizers/tableau_pybind_test.py

@@ -1,5 +1,3 @@
-# Copyright 2021 Google LLC
-#
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
@@ -56,6 +54,27 @@ def test_from_named_gate():
     with pytest.raises(IndexError, match="not unitary"):
         stim.Tableau.from_named_gate("X_ERROR")
 
+def test_from_state_vector():
+    t = stim.Tableau.from_state_vector([
+        0.5**0.5,
+        0,
+        0,
+        0.5**0.5,
+    ], endian='little')
+    assert len(t) == 2
+    assert t.x_output(0) == stim.PauliString("Z_")
+    assert t.x_output(1) == stim.PauliString("_X")
+    assert t.z_output(0) == stim.PauliString("XX")
+    assert t.z_output(1) == stim.PauliString("ZZ")
+
+    unnormalized = stim.Tableau.from_state_vector([
+        1,
+        0,
+        0,
+        1
+    ], endian='little')
+    assert unnormalized == t
+
 
 def test_identity():
     t = stim.Tableau(3)