Bug.warnings stochastic

doc/changes/2313.misc

@@ -0,0 +1 @@
+Add too small step warnings in fixed dt SODE solver

qutip/solver/sode/rouchon.py

@@ -1,4 +1,5 @@
 import numpy as np
+import warnings
 from qutip import unstack_columns, stack_columns
 from qutip.core import data as _data
 from ..stochastic import StochasticSolver
@@ -97,12 +98,16 @@ def set_state(self, t, state0, generator):
 
     def integrate(self, t, copy=True):
         delta_t = (t - self.t)
+        dt = self.options["dt"]
         if delta_t < 0:
             raise ValueError("Stochastic integration need increasing times")
-        elif delta_t == 0:
-            return self.t, self.state, np.zeros()
+        elif delta_t < 0.5 * dt:
+            warnings.warn(
+                f"Step under minimum step ({dt}), skipped.",
+                RuntimeWarning
+            )
+            return self.t, self.state, np.zeros(len(self.sc_ops))
 
-        dt = self.options["dt"]
         N, extra = np.divmod(delta_t, dt)
         N = int(N)
         if extra > 0.5 * dt:

qutip/solver/sode/sode.py

@@ -1,4 +1,5 @@
 import numpy as np
+import warnings
 from . import _sode
 from ..integrator.integrator import Integrator
 from ..stochastic import StochasticSolver, SMESolver
@@ -135,12 +136,16 @@ def __init__(self, rhs, options):
 
     def integrate(self, t, copy=True):
         delta_t = t - self.t
+        dt = self.options["dt"]
         if delta_t < 0:
-            raise ValueError("Stochastic integration time")
-        elif delta_t == 0:
+            raise ValueError("Integration time, can't be negative.")
+        elif delta_t < 0.5 * dt:
+            warnings.warn(
+                f"Step under minimum step ({dt}), skipped.",
+                RuntimeWarning
+            )
             return self.t, self.state, np.zeros(self.N_dw)
 
-        dt = self.options["dt"]
         N, extra = np.divmod(delta_t, dt)
         N = int(N)
         if extra > 0.5 * dt:

qutip/tests/solver/test_stochastic.py

@@ -348,23 +348,32 @@ def func(t, A, W):
 
 def test_deprecation_warnings():
     with pytest.warns(FutureWarning, match=r'map_func'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], map_func=None)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], map_func=None)
 
     with pytest.warns(FutureWarning, match=r'progress_bar'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], progress_bar=None)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], progress_bar=None)
 
     with pytest.warns(FutureWarning, match=r'nsubsteps'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], nsubsteps=None)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], nsubsteps=None)
 
     with pytest.warns(FutureWarning, match=r'map_func'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], map_func=None)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], map_func=None)
 
     with pytest.warns(FutureWarning, match=r'store_all_expect'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], store_all_expect=1)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], store_all_expect=1)
 
     with pytest.warns(FutureWarning, match=r'store_measurement'):
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], store_measurement=1)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], store_measurement=1)
 
     with pytest.raises(TypeError) as err:
-        ssesolve(qeye(2), basis(2), [0, 1e-5], [qeye(2)], m_ops=1)
+        ssesolve(qeye(2), basis(2), [0, 0.01], [qeye(2)], m_ops=1)
     assert '"m_ops" and "dW_factors"' in str(err.value)
+
+
+@pytest.mark.parametrize("method", ["euler", "rouchon"])
+def test_small_step_warnings(method):
+    with pytest.warns(RuntimeWarning, match=r'under minimum'):
+        smesolve(
+            qeye(2), basis(2), [0, 0.0000001], [qeye(2)],
+            options={"method": method}
+        )