Return Zernike values at a given set of x,y coords up to some maximum 
    radial order

def ZernikeSequence(x,y,maxRadial=5,epsilon=1e-10):
    """
    Return Zernike values at a given set of x,y coords up to some maximum 
    radial order
    """
    if maxRadial>5:
        raise ValueError('Code for higher radial orders not implemented')
    # Derive radius and exp(i*theta) 
    temp = x + 1j*y
    r1 = np.abs(temp)
    e1 = temp/(r1+epsilon)
     # Generate powers of r recursively
    r2 = r1*r1
    r3 = r2*r1
    r4 = r3*r1
    r5 = r4*r1
    # Generate cos and sin terms recursively from exp(i*theta)
    e2 = e1*e1
    e3 = e2*e1
    e4 = e3*e1
    e5 = e4*e1
    ctheta = e1.real
    stheta = e1.imag
    c2theta = e2.real
    s2theta = e2.imag
    c3theta = e3.real
    s3theta = e3.imag
    c4theta = e4.real
    s4theta = e4.imag
    c5theta = e5.real
    s5theta = e5.imag
    # Generate all the zernikes
    zernike = np.zeros((21,)+x.shape )
    zernike[0] =  1.0
    zernike[1] =  2.0*r1*ctheta
    zernike[2] =  2.0*r1*stheta
    zernike[3] =  sqrt(3.0)*(2.0*r2 - 1.0)
    zernike[4] =  sqrt(6.0)*r2*s2theta
    zernike[5] =  sqrt(6.0)*r2*c2theta
    zernike[6] =  sqrt(8.0)*(3.0*r3 - 2.0*r1)*stheta
    zernike[7] =  sqrt(8.0)*(3.0*r3 - 2.0*r1)*ctheta
    zernike[8] =  sqrt(8.0)*r3*s3theta
    zernike[9] = sqrt(8.0)*r3*c3theta
    zernike[10] = sqrt(5.0)*(6.*r4 - 6.*r2 + 1.)
    zernike[11] = sqrt(10.)*(4.*r4 - 3.*r2)*c2theta
    zernike[12] = sqrt(10.)*(4.*r4 - 3.*r2)*s2theta
    zernike[13] = sqrt(10.)*r4*c4theta
    zernike[14] = sqrt(10.)*r4*s4theta
    zernike[15] = sqrt(12.)*(10*r5-12*r3+3*r1)*ctheta
    zernike[16] = sqrt(12.)*(10*r5-12*r3+3*r1)*stheta
    zernike[17] = sqrt(12.)*(5*r5-4*r3)*c3theta
    zernike[18] = sqrt(12.)*(5*r5-4*r3)*s3theta
    zernike[19] = sqrt(12.)*r5*c5theta
    zernike[20] = sqrt(12.)*r5*s5theta
    # Make zernike zero outside unit circle (useful for dot product)
    zernike = zernike*np.less_equal(r1, 1.0)
    return(zernike[:NumZernike(maxRadial)])