Hi,
Negation is usually taken to be different than inversion (ie inverting the digital word). Inversion takes 1111 and produces 0000 but with negation it uses the twos complement negative value which is minus the value. So 1 would produce 1111 with a 4 bit word because 1111 means -1 in twos complement binary arithmetic. Actually 1 produces -1 but in binary that is 1111 not 0000.
Inverting 0001 produces 1110 but that is just simple inversion, not the same as negation.