Initialisation du repository de Beta

venv/lib/python3.12/site-packages/sympy/physics/quantum/shor.py

@@ -0,0 +1,173 @@
+"""Shor's algorithm and helper functions.
+
+Todo:
+
+* Get the CMod gate working again using the new Gate API.
+* Fix everything.
+* Update docstrings and reformat.
+"""
+
+import math
+import random
+
+from sympy.core.mul import Mul
+from sympy.core.singleton import S
+from sympy.functions.elementary.exponential import log
+from sympy.functions.elementary.miscellaneous import sqrt
+from sympy.core.intfunc import igcd
+from sympy.ntheory import continued_fraction_periodic as continued_fraction
+from sympy.utilities.iterables import variations
+
+from sympy.physics.quantum.gate import Gate
+from sympy.physics.quantum.qubit import Qubit, measure_partial_oneshot
+from sympy.physics.quantum.qapply import qapply
+from sympy.physics.quantum.qft import QFT
+from sympy.physics.quantum.qexpr import QuantumError
+
+
+class OrderFindingException(QuantumError):
+    pass
+
+
+class CMod(Gate):
+    """A controlled mod gate.
+
+    This is black box controlled Mod function for use by shor's algorithm.
+    TODO: implement a decompose property that returns how to do this in terms
+    of elementary gates
+    """
+
+    @classmethod
+    def _eval_args(cls, args):
+        # t = args[0]
+        # a = args[1]
+        # N = args[2]
+        raise NotImplementedError('The CMod gate has not been completed.')
+
+    @property
+    def t(self):
+        """Size of 1/2 input register.  First 1/2 holds output."""
+        return self.label[0]
+
+    @property
+    def a(self):
+        """Base of the controlled mod function."""
+        return self.label[1]
+
+    @property
+    def N(self):
+        """N is the type of modular arithmetic we are doing."""
+        return self.label[2]
+
+    def _apply_operator_Qubit(self, qubits, **options):
+        """
+            This directly calculates the controlled mod of the second half of
+            the register and puts it in the second
+            This will look pretty when we get Tensor Symbolically working
+        """
+        n = 1
+        k = 0
+        # Determine the value stored in high memory.
+        for i in range(self.t):
+            k += n*qubits[self.t + i]
+            n *= 2
+
+        # The value to go in low memory will be out.
+        out = int(self.a**k % self.N)
+
+        # Create array for new qbit-ket which will have high memory unaffected
+        outarray = list(qubits.args[0][:self.t])
+
+        # Place out in low memory
+        for i in reversed(range(self.t)):
+            outarray.append((out >> i) & 1)
+
+        return Qubit(*outarray)
+
+
+def shor(N):
+    """This function implements Shor's factoring algorithm on the Integer N
+
+    The algorithm starts by picking a random number (a) and seeing if it is
+    coprime with N. If it is not, then the gcd of the two numbers is a factor
+    and we are done. Otherwise, it begins the period_finding subroutine which
+    finds the period of a in modulo N arithmetic. This period, if even, can
+    be used to calculate factors by taking a**(r/2)-1 and a**(r/2)+1.
+    These values are returned.
+    """
+    a = random.randrange(N - 2) + 2
+    if igcd(N, a) != 1:
+        return igcd(N, a)
+    r = period_find(a, N)
+    if r % 2 == 1:
+        shor(N)
+    answer = (igcd(a**(r/2) - 1, N), igcd(a**(r/2) + 1, N))
+    return answer
+
+
+def getr(x, y, N):
+    fraction = continued_fraction(x, y)
+    # Now convert into r
+    total = ratioize(fraction, N)
+    return total
+
+
+def ratioize(list, N):
+    if list[0] > N:
+        return S.Zero
+    if len(list) == 1:
+        return list[0]
+    return list[0] + ratioize(list[1:], N)
+
+
+def period_find(a, N):
+    """Finds the period of a in modulo N arithmetic
+
+    This is quantum part of Shor's algorithm. It takes two registers,
+    puts first in superposition of states with Hadamards so: ``|k>|0>``
+    with k being all possible choices. It then does a controlled mod and
+    a QFT to determine the order of a.
+    """
+    epsilon = .5
+    # picks out t's such that maintains accuracy within epsilon
+    t = int(2*math.ceil(log(N, 2)))
+    # make the first half of register be 0's |000...000>
+    start = [0 for x in range(t)]
+    # Put second half into superposition of states so we have |1>x|0> + |2>x|0> + ... |k>x>|0> + ... + |2**n-1>x|0>
+    factor = 1/sqrt(2**t)
+    qubits = 0
+    for arr in variations(range(2), t, repetition=True):
+        qbitArray = list(arr) + start
+        qubits = qubits + Qubit(*qbitArray)
+    circuit = (factor*qubits).expand()
+    # Controlled second half of register so that we have:
+    # |1>x|a**1 %N> + |2>x|a**2 %N> + ... + |k>x|a**k %N >+ ... + |2**n-1=k>x|a**k % n>
+    circuit = CMod(t, a, N)*circuit
+    # will measure first half of register giving one of the a**k%N's
+
+    circuit = qapply(circuit)
+    for i in range(t):
+        circuit = measure_partial_oneshot(circuit, i)
+    # Now apply Inverse Quantum Fourier Transform on the second half of the register
+
+    circuit = qapply(QFT(t, t*2).decompose()*circuit, floatingPoint=True)
+    for i in range(t):
+        circuit = measure_partial_oneshot(circuit, i + t)
+    if isinstance(circuit, Qubit):
+        register = circuit
+    elif isinstance(circuit, Mul):
+        register = circuit.args[-1]
+    else:
+        register = circuit.args[-1].args[-1]
+
+    n = 1
+    answer = 0
+    for i in range(len(register)/2):
+        answer += n*register[i + t]
+        n = n << 1
+    if answer == 0:
+        raise OrderFindingException(
+            "Order finder returned 0. Happens with chance %f" % epsilon)
+    #turn answer into r using continued fractions
+    g = getr(answer, 2**t, N)
+    return g