add pop left and right for list

Author: brianz98

forte/api/sparse_operator_list_api.cc

@@ -148,6 +148,8 @@ void export_SparseOperatorList(py::module& m) {
                  }
              })
         .def("reverse", &SparseOperatorList::reverse, "Reverse the order of the operators")
+        .def("pop_left", &SparseOperatorList::pop_left, "Remove the leftmost operator")
+        .def("pop_right", &SparseOperatorList::pop_right, "Remove the rightmost operator")
         .def(
             "__call__",
             [](const SparseOperatorList& op, const size_t n) {

forte/helpers/math_structures.h

@@ -374,6 +374,19 @@ template <typename Derived, typename T, typename F> class VectorSpaceList {
         return it->second;
     }
 
+    /// @return a copy of the list with the leftmost element removed
+    Derived pop_left() {
+        assert(!elements_.empty());
+        elements_.erase(elements_.begin());
+        return static_cast<Derived&>(*this);
+    }
+
+    /// @return a copy of the list with the rightmost element removed
+    Derived pop_right() {
+        assert(!elements_.empty());
+        elements_.pop_back();
+        return static_cast<Derived&>(*this);
+    }
     /// @return the norm of the vector space
     /// @param p the norm to calculate (default is 2, -1 is infinity norm)
     double norm(int p = 2) const {

tests/pytest/sparse_ci/test_sparse_operator.py

@@ -513,6 +513,7 @@ def test_sparse_operator_list_remove():
     sopl = forte.SparseOperatorList()
     sopl.add("[1a+ 1a-]", 1.0)
     sopl.add("[0a+ 0a-]", 1.0)
+    sopl.add("[1a+ 1a-]", 1.0)
     sopl.remove("[1a+ 1a-]")
     assert len(sopl) == 1
 
@@ -528,6 +529,19 @@ def test_sparse_operator_list_add():
     assert sop3(1)[0].str() == "[0a+ 0a-]"
 
 
+def test_sparse_operator_list_pop():
+    sop = forte.SparseOperatorList()
+    sop.add("[1a+ 1a-]", 1.0)
+    sop.add("[0a+ 0a-]", 1.0)
+    sop.add("[1a+ 1a-]", 1.0)
+    assert len(sop) == 3
+    sop = sop.pop_left()
+    assert len(sop) == 2
+    sop = sop.pop_right()
+    assert len(sop) == 1
+    assert sop(0)[0].str() == "[0a+ 0a-]"
+
+
 if __name__ == "__main__":
     test_sparse_operator_creation()
     test_sparse_operator()
@@ -536,3 +550,4 @@ def test_sparse_operator_list_add():
     test_sparse_operator_list_reverse()
     test_sparse_operator_list_remove()
     test_sparse_operator_list_add()
+    test_sparse_operator_list_pop()