Added advanced version of quantum counting example

src/examples/quantum_counting_advanced.py

@@ -0,0 +1,62 @@
+'''Count the number of stable models of an ASP program using the naive Quantum Counting algorithm.
+
+Since example `quantum_counting' uses only 2 qubits, the precision of the resulting estimate of M \
+is very low. This example improves the estimate precision by adding a few qubits to the circuit.
+'''
+
+import math
+from src import qasp
+from src.examples.util import tab, pause
+
+# ASP program
+PRGM = '''
+    p :- not q.
+    q :- not p.
+    r :- p.
+    r :- q.
+'''
+
+# Hardcoded list of stable models
+STABLE_MODELS = [
+    [('p', True), ('q', False), ('r', True)],  # {p, r}
+    [('p', False), ('q', True), ('r', True)],  # {q, r}
+]
+
+
+def main():
+    '''Entrypoint.
+    '''
+    print(f'ASP program:\n{tab(PRGM.strip(), striplines=True)}\n')
+    pause()
+
+    # Program parameters
+    n = len(STABLE_MODELS[0])
+    print(f'Number of variables: {n}.')
+    print()
+    pause()
+
+    # Initialization algorithm
+    algorithm = qasp.init_algorithm.alg_grover(n)  # Walsh-Hadamard
+    print(f'Initialization algorithm:\n{tab(str(algorithm.draw()))}\n')
+    pause()
+
+    # Oracle
+    oracle = qasp.oracle.from_asp_stable_models(
+        STABLE_MODELS, var_order=['p', 'q', 'r'])
+    print(f'Quantum oracle:\n{tab(str(oracle[1].draw()))}\n')
+    pause()
+
+    # Simulation
+    m = 5  # NOTE: This is the only change from `quantum_counting' example
+    eps = 1/6
+    # pylint: disable=invalid-name
+    (circuit, _, M) = qasp.problems.estimation.exec_count(algorithm, oracle, m, eps)
+    print(f'Used circuit:\n{tab(str(circuit.draw()))}\n')
+    pause()
+    print(
+        f'Estimated number of solutions: {M.lower:.2f} <= M <= {M.upper:.2f}.')
+    print()
+
+
+if __name__ == '__main__':
+    main()