what is the meaning of the function logsumexp

[fgqile]

Why is the difference required after the maximum value is taken

the code is following

## Helper function for log sum exp calculation:
def logsumexp(inputs, dim=None, keepdim=False):
    if dim is None:
        inputs = inputs.view(-1)
        dim = 0
    s, _ = torch.max(inputs, dim=dim, keepdim=True)
    outputs = s + (inputs - s).exp().sum(dim=dim, keepdim=True).log()
    if not keepdim:
        outputs = outputs.squeeze(dim)
    return outputs