qiskit/quantum_info/synthesis/two_qubit_kak.py
def euler_angles_1q(unitary_matrix):
    """Compute Euler angles for a single-qubit gate.

    Find angles (theta, phi, lambda) such that
    unitary_matrix = phase * Rz(phi) * Ry(theta) * Rz(lambda)

    Args:
        unitary_matrix (ndarray): 2x2 unitary matrix

    Returns:
        tuple: (theta, phi, lambda) Euler angles of SU(2)

    Raises:
        QiskitError: if unitary_matrix not 2x2, or failure
    """
    if unitary_matrix.shape != (2, 2):
        raise QiskitError("euler_angles_1q: expected 2x2 matrix")
    phase = la.det(unitary_matrix)**(-1.0/2.0)
    U = phase * unitary_matrix  # U in SU(2)
    # OpenQASM SU(2) parameterization:
    # U[0, 0] = exp(-i(phi+lambda)/2) * cos(theta/2)
    # U[0, 1] = -exp(-i(phi-lambda)/2) * sin(theta/2)
    # U[1, 0] = exp(i(phi-lambda)/2) * sin(theta/2)
    # U[1, 1] = exp(i(phi+lambda)/2) * cos(theta/2)
    # Find theta
    if abs(U[0, 0]) > _CUTOFF_PRECISION:
        theta = 2 * math.acos(abs(U[0, 0]))
    else:
        theta = 2 * math.asin(abs(U[1, 0]))
    # Find phi and lambda
    phase11 = 0.0
    phase10 = 0.0
    if abs(math.cos(theta/2.0)) > _CUTOFF_PRECISION:
        phase11 = U[1, 1] / math.cos(theta/2.0)
    if abs(math.sin(theta/2.0)) > _CUTOFF_PRECISION:
        phase10 = U[1, 0] / math.sin(theta/2.0)
    phiplambda = 2 * math.atan2(np.imag(phase11), np.real(phase11))
    phimlambda = 2 * math.atan2(np.imag(phase10), np.real(phase10))
    phi = 0.0
    if abs(U[0, 0]) > _CUTOFF_PRECISION and abs(U[1, 0]) > _CUTOFF_PRECISION:
        phi = (phiplambda + phimlambda) / 2.0
        lamb = (phiplambda - phimlambda) / 2.0
    else:
        if abs(U[0, 0]) < _CUTOFF_PRECISION:
            lamb = -phimlambda
        else:
            lamb = phiplambda
    # Check the solution
    Rzphi = np.array([[np.exp(-1j*phi/2.0), 0],
                      [0, np.exp(1j*phi/2.0)]], dtype=complex)
    Rytheta = np.array([[np.cos(theta/2.0), -np.sin(theta/2.0)],
                        [np.sin(theta/2.0), np.cos(theta/2.0)]], dtype=complex)
    Rzlambda = np.array([[np.exp(-1j*lamb/2.0), 0],
                         [0, np.exp(1j*lamb/2.0)]], dtype=complex)
    V = np.dot(Rzphi, np.dot(Rytheta, Rzlambda))
    if la.norm(V - U) > _CUTOFF_PRECISION:
        raise QiskitError("euler_angles_1q: incorrect result")
    return theta, phi, lamb
def euler_angles_1q(unitary_matrix):
    """Compute Euler angles for a single-qubit gate.

    Find angles (theta, phi, lambda) such that
    unitary_matrix = phase * Rz(phi) * Ry(theta) * Rz(lambda)

    Args:
        unitary_matrix (ndarray): 2x2 unitary matrix

    Returns:
        tuple: (theta, phi, lambda) Euler angles of SU(2)

    Raises:
        QiskitError: if unitary_matrix not 2x2, or failure
    """
    if unitary_matrix.shape != (2, 2):
        raise QiskitError("euler_angles_1q: expected 2x2 matrix")
    phase = la.det(unitary_matrix)**(-1.0/2.0)
    U = phase * unitary_matrix  # U in SU(2)
    # OpenQASM SU(2) parameterization:
    # U[0, 0] = exp(-i(phi+lambda)/2) * cos(theta/2)
    # U[0, 1] = -exp(-i(phi-lambda)/2) * sin(theta/2)
    # U[1, 0] = exp(i(phi-lambda)/2) * sin(theta/2)
    # U[1, 1] = exp(i(phi+lambda)/2) * cos(theta/2)
    # Find theta
    if abs(U[0, 0]) > _CUTOFF_PRECISION:
        theta = 2 * math.acos(abs(U[0, 0]))
    else:
        theta = 2 * math.asin(abs(U[1, 0]))
    # Find phi and lambda
    phase11 = 0.0
    phase10 = 0.0
    if abs(math.cos(theta/2.0)) > _CUTOFF_PRECISION:
        phase11 = U[1, 1] / math.cos(theta/2.0)
    if abs(math.sin(theta/2.0)) > _CUTOFF_PRECISION:
        phase10 = U[1, 0] / math.sin(theta/2.0)
    phiplambda = 2 * math.atan2(np.imag(phase11), np.real(phase11))
    phimlambda = 2 * math.atan2(np.imag(phase10), np.real(phase10))
    phi = 0.0
    if abs(U[0, 0]) > _CUTOFF_PRECISION and abs(U[1, 0]) > _CUTOFF_PRECISION:
        phi = (phiplambda + phimlambda) / 2.0
        lamb = (phiplambda - phimlambda) / 2.0
    else:
        if abs(U[0, 0]) < _CUTOFF_PRECISION:
            lamb = -phimlambda
        else:
            lamb = phiplambda
    # Check the solution
    Rzphi = np.array([[np.exp(-1j*phi/2.0), 0],
                      [0, np.exp(1j*phi/2.0)]], dtype=complex)
    Rytheta = np.array([[np.cos(theta/2.0), -np.sin(theta/2.0)],
                        [np.sin(theta/2.0), np.cos(theta/2.0)]], dtype=complex)
    Rzlambda = np.array([[np.exp(-1j*lamb/2.0), 0],
                         [0, np.exp(1j*lamb/2.0)]], dtype=complex)
    V = np.dot(Rzphi, np.dot(Rytheta, Rzlambda))
    if la.norm(V - U) > _CUTOFF_PRECISION:
        raise QiskitError("euler_angles_1q: incorrect result")
    return theta, phi, lamb
Compute Euler angles for a single-qubit gate.

    Find angles (theta, phi, lambda) such that
    unitary_matrix = phase * Rz(phi) * Ry(theta) * Rz(lambda)

    Args:
        unitary_matrix (ndarray): 2x2 unitary matrix

    Returns:
        tuple: (theta, phi, lambda) Euler angles of SU(2)

    Raises:
        QiskitError: if unitary_matrix not 2x2, or failure