sentences:  The parity check matrix for a given code can be derived from its generator matrix (and vice versa).If the generator matrix for an ["n","k"]-code is in standard form 
  then the parity check matrix is given by
  because 
  Negation is performed in the finite field F"q".Note that if the characteristic of the underlying field is 2 (i.e., 1 + 1 = 0 in that field), as in binary codes, then -"P" = "P", so the negation is unnecessary.