Possible bug in beta schedule calculation

[matvogel]

I think there is a bug in your beta schedule calculation, as you go with the default beta_start value of 0.02 and only provide the end value of 1e-4. However, you scale the provided end value (beta_max in the configuration) with 1/N_timesteps while the start value of 0.02 is kept as is.

betas = make_beta_schedule(n_timestep=opt.interval, linear_end=opt.beta_max / opt.interval)

I guess that the values are taken from VPSDE (20 and 0.1) and and already scaled down by the number of timesteps (20/1000, 0.1/1000), so what you wanted to do is more something like this:

def make_beta_schedule(n_timestep=1000, linear_start=1e-4, linear_end=2e-2):
    # return np.linspace(linear_start, linear_end, n_timestep)
    scale = 1000 / n_timestep
    linear_start *= scale
    linear_end *= scale
    
    betas = torch.linspace(linear_start**0.5, linear_end**0.5, n_timestep, dtype=torch.float64) ** 2
    return betas.numpy()

betas = make_beta_schedule(n_timestep=opt.interval, linear_end=opt.beta_max)

Is this correct or is there areason to only scaling the linear_end variable?