def METHOD_NAME(self):
    nz = 4
    target, sens = self.problem_3d(3, nz)
    dim = target.shape[0]
    g, k1, t, s = rf.spiral_arch(0.24, dim, 4e-6, 200, 0.035)
    k1 = k1 / dim
    k1 = rf.stack_of(k1, nz, 0.1)
    A = rf.linop.PtxSpatialExplicit(
        sens, k1, dt=4e-6, img_shape=target.shape, b0=None
    )
    pulses = sp.mri.rf.stspa(
        target,
        sens,
        st=None,
        coord=k1,
        dt=4e-6,
        max_iter=30,
        alpha=10,
        tol=1e-3,
        phase_update_interval=200,
        explicit=True,
    )
    npt.assert_array_almost_equal(A * pulses, target, 1e-3)