function [h,err] = spike(g,n0,n)
%SPIKE	Finds the FIR least squares inverse of g(n)
%----
%USAGE:	[h,err] = spike(g,n0,n) 
%
%	g   : the filter that is to be inverted
%	n0  : the delay used in the minimization of
%		e(n)=g(n)*g(n) - delta(n-n0)
%	n   : order (number of coefficients) in h
%	h   : the FIR least squares inverse of g
%	err : squared error in the approximation
%
%---------------------------------------------------------------
% copyright 1996, by M.H. Hayes.  For use with the book 
% "Statistical Digital Signal Processing and Modeling"
% (John Wiley & Sons, 1996).
%---------------------------------------------------------------

g   = g(:);
m   = length(g);
if m+n-1<=n0, error('Delay too large'), end
G   = convm(g,n);
d   = zeros(m+n-1,1);
d(n0+1) = 1;
h   = G\d;
err = 1 - G(n0+1,:)*h;
end;