Applied changes suggested by @hodgestar

doc/apidoc/apidoc.rst

@@ -13,6 +13,7 @@ complete list of QuTiP's public classes and functions.
    quantumobject.rst
    time_dep.rst
    solver.rst
+   environments.rst
    heom.rst
    piqs.rst
    visualization.rst

doc/apidoc/environments.rst

@@ -0,0 +1,52 @@
+************
+Environments
+************
+
+Bosonic Environments
+--------------------
+
+.. autoclass:: qutip.core.BosonicEnvironment
+    :members:
+
+.. autoclass:: qutip.core.DrudeLorentzEnvironment
+    :members:
+    :inherited-members:
+    :show-inheritance:
+    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
+
+.. autoclass:: qutip.core.UnderDampedEnvironment
+    :members:
+    :inherited-members:
+    :show-inheritance:
+    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
+
+.. autoclass:: qutip.core.OhmicEnvironment
+    :members:
+    :inherited-members:
+    :show-inheritance:
+    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
+
+.. autoclass:: qutip.core.CFExponent
+    :members:
+
+.. autoclass:: qutip.core.ExponentialBosonicEnvironment
+    :members:
+    :show-inheritance:
+
+.. autofunction:: qutip.core.environment.system_terminator
+
+
+Fermionic Environments
+----------------------
+
+.. autoclass:: qutip.core.FermionicEnvironment
+    :members:
+    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
+
+.. autoclass:: qutip.core.LorentzianEnvironment
+    :members:
+    :show-inheritance:
+
+.. autoclass:: qutip.core.ExponentialFermionicEnvironment
+    :members:
+    :show-inheritance:

doc/apidoc/heom.rst

@@ -1,58 +1,3 @@
-************
-Environments
-************
-
-Bosonic Environments
---------------------
-
-.. autoclass:: qutip.core.BosonicEnvironment
-    :members:
-
-.. autoclass:: qutip.core.DrudeLorentzEnvironment
-    :members:
-    :inherited-members:
-    :show-inheritance:
-    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
-
-.. autoclass:: qutip.core.UnderDampedEnvironment
-    :members:
-    :inherited-members:
-    :show-inheritance:
-    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
-
-.. autoclass:: qutip.core.OhmicEnvironment
-    :members:
-    :inherited-members:
-    :show-inheritance:
-    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
-
-.. autoclass:: qutip.core.CFExponent
-    :members:
-
-.. autoclass:: qutip.core.ExponentialBosonicEnvironment
-    :members:
-    :show-inheritance:
-
-.. autofunction:: qutip.core.environment.system_terminator
-
-
-Fermionic Environments
-----------------------
-
-.. autoclass:: qutip.core.FermionicEnvironment
-    :members:
-    :exclude-members: from_correlation_function, from_power_spectrum, from_spectral_density
-
-.. autoclass:: qutip.core.LorentzianEnvironment
-    :members:
-    :show-inheritance:
-
-.. autoclass:: qutip.core.ExponentialFermionicEnvironment
-    :members:
-    :show-inheritance:
-
-
-
 ********************************
 Hierarchical Equations of Motion
 ********************************

qutip/solver/brmesolve.py

@@ -206,7 +206,7 @@ def brmesolve(
             new_a_ops.append((a_op, spectra))
         elif isinstance(spectra, BosonicEnvironment):
             spec = SpectraCoefficient(
-                coefficient(lambda w: spectra.power_spectrum(w))
+                coefficient(spectra.power_spectrum)
             )
             new_a_ops.append((a_op, spec))
         elif callable(spectra):

qutip/solver/heom/bofin_solvers.py

@@ -733,15 +733,9 @@ def _combine_bath_exponents(self, bath):
         if (not isinstance(bath, (list, tuple))
                 or self._is_environment_api(bath)):
             bath = [bath]
+        bath = [self._to_bath(b) for b in bath]
         exponents = []
         for b in bath:
-            if self._is_environment_api(b):
-                b = self._env_to_bath(b)
-            if (isinstance(b, (BosonicEnvironment, FermionicEnvironment))
-                    and not isinstance(b, (BosonicBath, FermionicBath))):
-                raise ValueError("Environments must be passed with their"
-                                 " corresponding coupling operator as a list"
-                                 " or tuple (env, Q)")
             exponents.extend(b.exponents)
 
         if not all(exp.Q.dims == exponents[0].Q.dims for exp in exponents):
@@ -753,37 +747,38 @@ def _combine_bath_exponents(self, bath):
         return exponents
 
     def _is_environment_api(self, bath_spec):
-        is_list = isinstance(bath_spec, (list, tuple))
-        if not is_list:
+        if not isinstance(bath_spec, (list, tuple)) or len(bath_spec) < 2:
             return False
+        env, Q, *args = bath_spec
 
-        starts_with_env = isinstance(
-            bath_spec[0], (BosonicEnvironment, FermionicEnvironment)
-        )
-        if not starts_with_env:
+        if not isinstance(env, (BosonicEnvironment, FermionicEnvironment)):
             return False
 
-        contains_bath = any(
-            isinstance(elem, (Bath, BosonicBath, FermionicBath))
-            for elem in bath_spec
-        )
-        if contains_bath:
-            # Potentially confused user, passed mixed list of environments
-            # and baths. Error will be raised elsewhere.
+        if not isinstance(Q, (Qobj, QobjEvo)):
             return False
 
         return True
 
-    def _env_to_bath(self, bath_spec):
-        if isinstance(bath_spec[0], ExponentialBosonicEnvironment):
-            return BosonicBath.from_environment(*bath_spec)
-        if isinstance(bath_spec[0], ExponentialFermionicEnvironment):
-            return FermionicBath.from_environment(*bath_spec)
-        else:
-            raise ValueError("The HEOM solver requires the environment to have"
-                             " a multi-exponential correlation function. Use"
-                             " one of the `approx_by_` functions to generate a"
-                             " multi-exponential approximation.")
+    def _to_bath(self, bath_spec):
+        if isinstance(bath_spec, (Bath, BosonicBath, FermionicBath)):
+            return bath_spec
+
+        if not self._is_environment_api(bath_spec):
+            raise ValueError(
+                "Environments must be passed as either Bath instances or"
+                " as a tuple or list corresponding to an environment and a"
+                " coupling operator, (env, Q)"
+            )
+        env, Q, *args = bath_spec
+
+        if isinstance(env, ExponentialBosonicEnvironment):
+            return BosonicBath.from_environment(env, Q, *args)
+        if isinstance(env, ExponentialFermionicEnvironment):
+            return FermionicBath.from_environment(env, Q, *args)
+        raise ValueError("The HEOM solver requires the environment to have"
+                        " a multi-exponential correlation function. Use"
+                        " one of the `approx_by_` functions to generate a"
+                        " multi-exponential approximation.")
 
     def _grad_n(self, he_n):
         """ Get the gradient for the hierarchy ADO at level n. """

qutip/utilities.py

@@ -349,13 +349,18 @@ def _version2int(version_string):
 #
 
 def iterated_fit(
-    fun: Callable[..., complex], num_params: int,
-    xdata: ArrayLike, ydata: ArrayLike,
+    fun: Callable[..., complex],
+    num_params: int,
+    xdata: ArrayLike,
+    ydata: ArrayLike,
     target_rmse: float = 1e-5,
-    Nmin: int = 1, Nmax: int = 10,
+    Nmin: int = 1,
+    Nmax: int = 10,
     guess: ArrayLike | Callable[[int], ArrayLike] = None,
-    lower: ArrayLike = None, upper: ArrayLike = None,
-    sigma: float | ArrayLike = None, maxfev: int = None
+    lower: ArrayLike = None,
+    upper: ArrayLike = None,
+    sigma: float | ArrayLike = None,
+    maxfev: int = None
 ) -> tuple[float, ArrayLike]:
     r"""
     Iteratively tries to fit the given data with a model of the form