For #2305

Qiskit · Feb 8, 2025 · b9714c0 · b9714c0
1 parent f1edeed
commit b9714c0
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Showing 4 changed files with 17 additions and 7 deletions.
diff --git a/releasenotes/notes/removed-useless-code-MPS-simulator-98ca4717e0612ac2.yaml b/releasenotes/notes/removed-useless-code-MPS-simulator-98ca4717e0612ac2.yaml
@@ -0,0 +1,14 @@
+---
+prelude: >
+    Removed code that was never executed in ``MPS::sample_measure``, also removed
+    the ``shots`` parameter as it wasn't used.
+features:
+  - |
+    Probably the compiler can optimize out those things, but the code is cleaner
+    this way. The ``params`` parameter was removed from ``MPS::sample_measure``
+    as it's not used, also a check and unreacheable code from the same function
+    is removed.
+  - |
+    There is no change in behaviour, just code cleanup.
+    Refer to `#2305 <https://github.com/Qiskit/qiskit-aer/issues/2305>`
+    for more details.
diff --git a/src/simulators/matrix_product_state/matrix_product_state.hpp b/src/simulators/matrix_product_state/matrix_product_state.hpp
@@ -801,7 +801,7 @@ std::vector<SampleVector> State::sample_measure_all(uint_t shots,
 
 #pragma omp parallel for if (getenv("PRL_PROB_MEAS"))
   for (int_t i = 0; i < static_cast<int_t>(shots); i++) {
-    auto single_result = qreg_.sample_measure(shots, rng);
+    auto single_result = qreg_.sample_measure(rng);
     all_samples[i].from_vector(single_result);
   }
   return all_samples;

diff --git a/src/simulators/matrix_product_state/matrix_product_state_internal.cpp b/src/simulators/matrix_product_state/matrix_product_state_internal.cpp
@@ -1637,7 +1637,7 @@ reg_t MPS::sort_measured_values(const reg_t &input_outcome,
 //        probability. We then update 'mat' by contracting it with the suitable
 //        matrix (0 or 1).
 
-reg_t MPS::sample_measure(uint_t shots, RngEngine &rng) const {
+reg_t MPS::sample_measure(RngEngine &rng) const {
   double prob = 1;
   reg_t current_measure(num_qubits_);
   cmatrix_t mat;
@@ -1683,10 +1683,6 @@ uint_t MPS::sample_measure_single_qubit(uint_t qubit, double &prob, double rnd,
   // measurement outcome
   if (qubit == 0) {
     mat = q_reg_[qubit].get_data(measurement);
-    if (qubit != 0) // multiply mat by left lambda
-      for (uint_t col = 0; col < mat.GetColumns(); col++)
-        for (uint_t row = 0; row < mat.GetRows(); row++)
-          mat(row, col) *= lambda_reg_[qubit - 1][row];
   } else {
     mat = mat * q_reg_[qubit].get_data(measurement);
   }

diff --git a/src/simulators/matrix_product_state/matrix_product_state_internal.hpp b/src/simulators/matrix_product_state/matrix_product_state_internal.hpp
@@ -351,7 +351,7 @@ class MPS {
 
   reg_t apply_measure(const reg_t &qubits, const rvector_t &rnds);
   reg_t apply_measure_internal(const reg_t &qubits, const rvector_t &rands);
-  reg_t sample_measure(uint_t shots, RngEngine &rng) const;
+  reg_t sample_measure(RngEngine &rng) const;
 
   //----------------------------------------------------------------
   // Function name: initialize_from_statevector_internal