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function w = chebwin (m, at)
funcprot(0);
rhs= argn(2);
if (rhs < 1 | rhs > 2)
error("Wrong Number of input arguments");
elseif (~ (isscalar (m) & (m == fix (m)) & (m > 0)))
error ("chebwin: M must be a positive integer");
elseif (rhs == 1)
at = 100;
elseif (~ (isscalar (at) & isreal(at)))
error ("chebwin: AT must be a real scalar");
end
if (m == 1)
w = 1;
else
// beta calculation
gamma = 10^(-at/20);
beta = cosh(1/(m-1) * acosh(1/gamma));
// freq. scale
k = (0:m-1);
x = beta*cos(%pi*k/m);
// Chebyshev window (freq. domain)
p = cheb(m-1, x);
// inverse Fourier transform
if (modulo(m,2))
w = real(fft(p));
M = (m+1)/2;
w = w(1:M)/w(1);
w = [w(M:-1:2) w]';
else
//half-sample delay (even order)
p = p.*exp(%i*%pi/m * (0:m-1));
w = real(fft(p));
M = m/2+1;
w = w/w(2);
w = [w(M:-1:2) w(2:M)]';
end
end
endfunction
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