refactor to get children buffers at optimal parameters in the case the same...

refactor to get children buffers at optimal parameters in the case the same parameter is run multiple times (like in shots mode)
Signed-off-by: Alex McCaskey <mccaskeyaj@ornl.gov>

quantum/plugins/algorithms/vqe/vqe.cpp

@@ -96,9 +96,12 @@ void VQE::execute(const std::shared_ptr<AcceleratorBuffer> buffer) const {
                 "valid Optimizer.");
   }
 
+  std::vector<std::shared_ptr<AcceleratorBuffer>> min_child_buffers;
+
   // auto kernels = observable->observe(xacc::as_shared_ptr(kernel));
   // Cache of energy values during iterations.
   std::vector<double> energies;
+  double last_energy = std::numeric_limits<double>::max();
 
   // Here we just need to make a lambda kernel
   // to optimize that makes calls to the targeted QPU.
@@ -264,6 +267,16 @@ void VQE::execute(const std::shared_ptr<AcceleratorBuffer> buffer) const {
         xacc::info(ss.str());
         // Saves the energy value.
         energies.emplace_back(energy);
+
+        if (energy < last_energy) {
+          min_child_buffers.clear();
+          min_child_buffers.push_back(idBuffer);
+          for (auto b : buffers) {
+            min_child_buffers.push_back(b);
+          } 
+          last_energy = energy;
+        }
+
         return energy;
       },
       kernel->nVariables());
@@ -271,11 +284,9 @@ void VQE::execute(const std::shared_ptr<AcceleratorBuffer> buffer) const {
   auto result = optimizer->optimize(f);
 
   // Get the children at the opt-params
-  auto children_at_final_parameters =
-      buffer->getChildren("parameters", result.second);
   std::vector<double> opt_exp_vals, children_coeffs;
   std::vector<std::string> children_names;
-  for (auto &child : children_at_final_parameters) {
+  for (auto &child : min_child_buffers) {
     if (!child->hasExtraInfoKey("is-gradient-calc")) {
       opt_exp_vals.push_back(child->getInformation("exp-val-z").as<double>());
 
@@ -283,7 +294,7 @@ void VQE::execute(const std::shared_ptr<AcceleratorBuffer> buffer) const {
       children_coeffs.push_back(
           child->getInformation("coefficient").as<double>());
       children_names.push_back(child->name());
-    }
+    } 
   }
 
   buffer->addExtraInfo("opt-exp-vals", opt_exp_vals);