def _coeff4(N, a0, a1, a2, a3):
if N == <NUM_LIT:1>:<EOL><INDENT>return ones(<NUM_LIT:1>)<EOL><DEDENT>n = arange(<NUM_LIT:0>, N)<EOL>N1 = N - <NUM_LIT:1.><EOL>w = a0 -a1*cos(<NUM_LIT>*pi*n / N1) + a2*cos(<NUM_LIT>*pi*n / N1) - a3*cos(<NUM_LIT>*pi*n / N1)<EOL>return w<EOL>
a common internal function to some window functions with 4 coeffs


    For the blackmna harris for instance, the results are identical to octave if N is odd
    but not for even values...if n =0 whatever N is, the w(0) must be equal to a0-a1+a2-a3, which
    is the case here, but not in octave...