def initCalc(hOverR, R0, boxwidth, nParticles, nSmooth=32, ndim=3):
    """
    Initial derivations from settings
    
    Parameters
    ----------
    hOverR  : float
        Ratio of scale height to distance from star
    RO : float
        Distance to star
    boxwidth : float
        Width of the simulation box.  Height will be set as a large number
    nParticles : int
        Number of particles
    nSmooth : int
        Number of neighbors to smooth over for the simulation
    ndim : int
        Number of dimensions running in
    """
    # Initial derivations
    H = hOverR * R0
    # Assuming G = 1 and Mstar = 1 in code units:
    omega0 = R0**(-1.5)
    cs = H * omega0
    volume = H * boxwidth**(ndim-1)
    smooth = (float(nSmooth) * (volume)/nParticles)**(1./ndim) # approx smooth length
    boxshape = [boxwidth, boxwidth, 2*H]
    # Time stepping for gas settling
    tCourant = smooth/cs
    dDelta = tCourant/10.
    
    return H, cs, smooth, boxshape, dDelta