function [f,df,ddf]=isolation_filter(w,amp,leg,l,time)
% MATLAB HELP:
% 
% function [f,df,ddf]=isolation_filter(w,amp,leg,l,time)
%
% inputs:
%   w, frequencies
%   amp, amplitudes for the modes
%   leg, legendre polynomials
%   l,angular degree
%   time, time grid to compute on
% outputs:
%   f, the zero order singal
%   df, time derivative of f
%   ddf, second time derivate of f
%
%
%
% aaron birch, may 21, 2002

f=zeros(size(time));
df=zeros(size(time));
ddf=zeros(size(time));

for (i=1:length(amp))
        a= -1*( (2*l(i)+1)/4/pi)*leg(i);
	f=f+amp(i)*a*cos(w(i)*time);
	df=df-w(i)*amp(i)*a*sin(w(i)*time);
	ddf=ddf-w(i)*w(i)*amp(i)*a*cos(w(i)*time);
end;