用迭代法求Daubechies小波的尺度函数

 
p = [0.683013,1.183013,0.316987,-0.183013];
N = 20;
phi_before = 1;
for i = 1:N;
    phi_after = conv(p,phi_before);
    n = length(phi_after);
    phi_before(1:2:2*n) = phi_after;
end
k = 0:n-1;
x = 3*k/n;
plot(x,phi_after);