From 76b265a3f5d0a1c1011cd80eb450c17c695d71d1 Mon Sep 17 00:00:00 2001
From: Michael Goerz <mail@michaelgoerz.net>
Date: Wed, 8 Apr 2026 08:29:24 -0400
Subject: [PATCH] Add simplified constructor for `GradgenOperator`

---
 src/gradgen_operator.jl | 12 +++++++++++-
 test/test_gradgen.jl    |  3 +++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/gradgen_operator.jl b/src/gradgen_operator.jl
index 896ac9b..8c4a4be 100644
--- a/src/gradgen_operator.jl
+++ b/src/gradgen_operator.jl
@@ -12,6 +12,8 @@ import QuantumControl.QuantumPropagators.Interfaces:
 using QuantumPropagators.Controls: evaluate
 
 G::GradgenOperator = evaluate(gradgen::GradGenerator; vals_dict)
+
+G = GradgenOperator(G.G, G.control_deriv_ops)
 ```
 
 is the result of plugging in specific values for all controls in a
@@ -26,6 +28,14 @@ struct GradgenOperator{num_controls,GT,CGT}
 end
 
 
+function GradgenOperator(G, control_deriv_ops)
+    num_controls = length(control_deriv_ops)
+    GT = typeof(G)
+    CGT = eltype(control_deriv_ops)
+    return GradgenOperator{num_controls,GT,CGT}(G, control_deriv_ops)
+end
+
+
 function get_controls(O1::GradgenOperator)
     return Tuple([])
 end
@@ -34,7 +44,7 @@ end
 function random_state(H::GradgenOperator; rng = GLOBAL_RNG, _...)
     state = random_state(H.G; rng)
     num_controls = length(H.control_deriv_ops)
-    grad_states = [random_state(H.G; rng) for i ∈ eachindex(H.control_deriv_ops)]
+    grad_states = [random_state(H.G; rng) for _ in eachindex(H.control_deriv_ops)]
     return GradVector{num_controls,typeof(state)}(state, grad_states)
 end
 
diff --git a/test/test_gradgen.jl b/test/test_gradgen.jl
index f498bdb..230dd4d 100644
--- a/test/test_gradgen.jl
+++ b/test/test_gradgen.jl
@@ -32,6 +32,9 @@ using QuantumPropagators.Controls: evaluate
     G̃ = evaluate(G̃_of_t; vals_dict)
     Ĥ = evaluate(Ĥ_of_t; vals_dict)
 
+    G̃2 = GradgenOperator(G̃.G, G̃.control_deriv_ops)
+    @test G̃2 == G̃
+
     Û_Ψ = exp(-𝕚 * Ĥ * dt) * Ψ
 
     num_controls = length(Ĥ_of_t) - 1