function [y,v] = ppint(x,h,L);

% Synopsis: [y,v] = ppint(x,h,L).

% L-fold expansion and convolution, by polyphase decomposition.

% Input parameters:

% x: the input sequence

% h: the FIR filter coefficients

% L: the expansion factor.

% Output parameters:

% y: the output sequence.
% v: the output of each polyphase decomposition filter



% Part of software package for the book:

% A Course in Digital Signal Processing

% by Boaz Porat, John Wiley & Sons, 1997



lh = length(h); lq = floor((lh-1)/L) + 1;

q = flipud(reshape([reshape(h,1,lh),zeros(1,lq*L-lh)],L,lq));

lx = length(x); ly = lx*L+lh-1;

lv =lx + lq; % length of decimated sequences

v = zeros(L,lv);

for l = 1:L, v(l,1:lv-1) = conv(x,q(l,:)); end

y = reshape(flipud(v),1,L*lv);

y = y(1:ly);