small changes

qadence_libs/qinfo_tools/qfi.py

@@ -10,10 +10,10 @@
 from qadence_libs.qinfo_tools.utils import hessian
 
 
-def _symsqrt(A: Tensor) -> Tensor:
-    """Computes the square root of a Symmetric or Hermitian positive definite matrix.
+def _positive_semidefinite_sqrt(A: Tensor) -> Tensor:
+    """Computes the square root of a real positive semi-definite matrix.
 
-    Code from https://github.com/pytorch/pytorch/issues/25481#issuecomment-1032789228
+    Code taken from https://github.com/pytorch/pytorch/issues/25481#issuecomment-1032789228
     """
     L, Q = torch.linalg.eigh(A)
     zero = torch.zeros((), device=L.device, dtype=L.dtype)
@@ -149,7 +149,7 @@ def get_quantum_fisher_spsa(
         qfi_mat_estimator = a_k * (iteration * previous_qfi_estimator + qfi_mat)  # type: ignore
 
     # Get the positive-semidefinite version of the matrix for the update rule in QNG
-    qfi_mat_positive_sd = _symsqrt(torch.matmul(qfi_mat_estimator, qfi_mat_estimator))
+    qfi_mat_positive_sd = _positive_semidefinite_sqrt(qfi_mat_estimator @ qfi_mat_estimator)
     qfi_mat_positive_sd = qfi_mat_positive_sd + beta * torch.eye(ovrlp_model.num_vparams)
     qfi_mat_positive_sd = qfi_mat_positive_sd / (1 + beta)  # regularization
 

qadence_libs/qinfo_tools/qng.py

@@ -63,8 +63,8 @@ def __init__(
         if isinstance(model, TransformedModule):
             logger.warning(
                 "The model is of type '<class TransformedModule>. "
-                "Keep in mind that the QNG optimizer can only optimize circuit variational "
-                "parameter. Input and output shifting/scaling parameters will not be optimized."
+                "Keep in mind that the QNG optimizer can only optimize circuit "
+                "parameters. Input and output shifting/scaling parameters will not be optimized."
             )
             # Retrieve the quantum model from the TransformedModule
             model = model.model

tests/qinfo_tools/test_qng.py

@@ -51,6 +51,20 @@ def sin_dataset(samples: int) -> tuple[Tensor, Tensor]:
 DATASETS = [quadratic_dataset(samples), sin_dataset(samples)]
 
 
+def test_parameter_ordering(basic_optim_model: QuantumCircuit) -> None:
+    model = basic_optim_model
+    model.reset_vparams(torch.rand((len(model.vparams))))
+    vparams_torch = [p.data for p in model.parameters() if p.requires_grad]
+    vparams_qadence = [v.data for v in model.vparams.values()]
+    assert len(vparams_torch) == len(vparams_qadence)
+    msg = (
+        "The ordering of the output of the `vparams()` method in QuantumModel"
+        + "and the `parameters()` method in Torch is not consistent"
+        + "for variational parameters."
+    )
+    assert vparams_torch == vparams_qadence, msg
+
+
 @pytest.mark.parametrize("dataset", DATASETS)
 @pytest.mark.parametrize("optim_config", OPTIMIZERS_CONFIG)
 def test_optims(
@@ -76,17 +90,3 @@ def test_optims(
     if config["approximation"] == FisherApproximation.SPSA:
         assert optimizer.state["state"]["iter"] == iters
         assert optimizer.state["state"]["qfi_estimator"] is not None
-
-
-def test_parameter_ordering(basic_optim_model: QuantumCircuit) -> None:
-    model = basic_optim_model
-    model.reset_vparams(torch.rand((len(model.vparams))))
-    vparams_torch = [p.data for p in model.parameters() if p.requires_grad]
-    vparams_qadence = [v.data for v in model.vparams.values()]
-    assert len(vparams_torch) == len(vparams_qadence)
-    msg = (
-        "The ordering of the output of the `vparams()` method in QuantumModel"
-        + "and the `parameters()` method in Torch is not consistent"
-        + "for variational parameters."
-    )
-    assert vparams_torch == vparams_qadence, msg