import torch


def get_transformer_fwd_mask(s):
    """
    Generates a mask that looks like this:
        0, -inf, -inf
        0,   0,  -inf
        0,   0,  0

    Args:
        s: int
            the size of each sidelength of the mask
    """
    return torch.triu(torch.ones(s,s)*float("-inf"), diagonal=1)