Clean up earlier expectation from samples code

Also fixes documentation line in `pyproject.toml`

pyproject.toml

@@ -6,7 +6,7 @@ authors = ["The Qibo team"]
 license = "Apache License 2.0"
 readme = "README.md"
 repository = "https://github.com/qiboteam/qibochem/"
-documentation = ""
+documentation = "https://qibo.science/qibochem/latest/"
 keywords = []
 classifiers = [
   "Programming Language :: Python :: 3",

src/qibochem/measurement/expectation.py

@@ -3,73 +3,6 @@
 from qibo.hamiltonians import SymbolicHamiltonian
 from qibo.symbols import Z
 
-from qibochem.measurement.basis_rotate import measure_rotate_basis
-
-
-def pauli_expectation_shots(qc, nshots):
-    """
-    Calculates expectation value of circuit for pauli string from shots
-
-    Args:
-        qc: quantum circuit with appropriate rotations and measure gates
-        nshots: number of shots
-
-    Returns:
-        expectation: expectation value
-    """
-    result = qc.execute(nshots=nshots)
-    meas = result.frequencies(binary=True)
-
-    bitcount = 0
-    for bitstring, count in meas.items():
-        if bitstring.count("1") % 2 == 0:
-            bitcount += count
-        else:
-            bitcount -= count
-    expectation = bitcount / nshots
-    return expectation
-
-
-def circuit_expectation_shots(qc, of_qubham, nshots=1000):
-    """
-    Calculates expectation value of qubit hamiltonian w.r.t. circuit ansatz using shots
-
-    Args:
-        qc: Quantum circuit with ansatz
-        of_qubham: Molecular Hamiltonian given as an OpenFermion QubitOperator
-
-    Returns:
-        Expectation value of of_qubham w.r.t. circuit ansatz
-    """
-    # nterms = len(of_qubham.terms)
-    nqubits = qc.nqubits
-    # print(nterms)
-    coeffs = []
-    strings = []
-
-    expectation = 0
-    for qubop in of_qubham.terms:
-        coeffs.append(of_qubham.terms[qubop])
-        strings.append([qubop])
-
-    istring = 0
-    for pauli_op in strings:
-        if len(pauli_op[0]) == 0:  # no pauli obs to measure,
-            expectation += coeffs[istring]
-            # print(coeffs[istring])
-        else:
-            # add rotation gates to rotate pauli observable to computational basis
-            # i.e. X to Z, Y to Z
-            meas_qc = measure_rotate_basis(pauli_op[0], nqubits)
-            full_qc = qc + meas_qc
-            # print(full_qc.draw())
-            pauli_op_exp = pauli_expectation_shots(full_qc, nshots)
-            expectation += coeffs[istring] * pauli_op_exp
-            ## print(pauli_op, pauli_op_exp, coeffs[istring])
-        istring += 1
-
-    return expectation
-
 
 def expectation(
     circuit: qibo.models.Circuit, hamiltonian: SymbolicHamiltonian, from_samples=False, n_shots=1000
@@ -82,7 +15,7 @@ def expectation(
         circuit (qibo.models.Circuit): Quantum circuit ansatz
         hamiltonian (SymbolicHamiltonian): Molecular Hamiltonian
         from_samples: Whether the expectation value calculation uses samples or the simulated
-            state vector. Default: False, state vector simulation
+            state vector. Default: False; Results are from a state vector simulation
         n_shots: Number of times the circuit is run for the from_samples=True case
 
     Returns: