The filterdemo computes a FIR lowpass filter by solving a linear program.
It solves a discretization of the problem
minimize d2
subject to -1/d1 <= H(wk) <= d1, 0 <= w <= wc
max(abs(H(wk))) <= d2, ws <= w <= pi
where H(w) = h_0 + sum_{i=1}^{n-1} h_i*cos(2*pi/n*i*w).
The variables are h and d2.
'filterdemo_cli' uses a simple a simple command-line interface.
'filterdemo_gui' uses a graphical user interface based on GTK.