theory: bound both sides of residual stability

1 files changed, 5 insertions, 0 deletions

diff --git a/experiments/verify_theory.py b/experiments/verify_theory.py
index ad0e9b9..d4325e9 100644
--- a/experiments/verify_theory.py
+++ b/experiments/verify_theory.py
@@ -220,18 +220,23 @@ def check_residual_coupling_instability():
 
     positive_k = 0.02
     negative_k = -0.20
+    too_negative_k = -40.0
     positive_radius = radius(positive_k)
     negative_radius = radius(negative_k)
+    too_negative_radius = radius(too_negative_k)
     polynomial_at_one = -eta * positive_k
     print("\nMULTIPLICATIVE RESIDUAL COUPLING")
     print(f"vectorization_error={identity_error:.3e} "
           f"rho(k={positive_k:+.3f})={positive_radius:.9f} "
           f"rho(k={negative_k:+.3f})={negative_radius:.9f} "
+          f"rho(k={too_negative_k:+.1f})={too_negative_radius:.9f} "
           f"p_positive(1)={polynomial_at_one:+.3e}")
     assert identity_error < 2e-15
     assert polynomial_at_one < 0.0
     assert positive_radius > 1.0
     assert negative_radius < 1.0
+    assert too_negative_k < -2.0 * (1.0 + momentum) / eta
+    assert too_negative_radius > 1.0
 
 
 def check_intermittent_feedback_tracking():