def MHCDEigenFrequencies(dg, r, Uhv=4000.0, rho=1.2041, yDirNum=4, xDirNum=4):
    """Eigenfrequency calculatioon of a micro hollow cathode discharge.

    Args:
        dg      :   Distance of electrodes (discharge gap).
        r       :   Radius of the discharge hole.
        Uhv     :   Voltage between electrodes.
        rho     :   Gas density.
        yDirNum :   Col Number of eigenfrequencies.
        xDirNum :   Row number of eigenfrequencies.

    Returns:
        Returns the eigenfrequencies of the discharge.

    """
    from scipy.special import jn, jn_zeros
    import numpy as np
    k = 3
    e0 = 8.854187817e-12
    vm = np.sqrt(e0 / rho) * Uhv / dg
    bessel_roots = np.zeros((xDirNum, yDirNum))
    for x in range(0, xDirNum):
        b = jn_zeros(x, yDirNum)
        for y in range(0, yDirNum):
            bessel_roots[y][x] = b[y]
    f = bessel_roots * vm * k / (2 * np.pi * r)
    return f
