## Copyright (C) 2018 Jens Ahrensfeld
## 
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or
## (at your option) any later version.
## 
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## 
## You should have received a copy of the GNU General Public License
## along with this program.  If not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*- 
## @deftypefn {Function File} {@var{retval} =} im_eval (@var{input1}, @var{input2})
##
## @seealso{}
## @end deftypefn

## Author: Jens Ahrensfeld <ahrensfeld@w2ess001vm>
## Created: 2018-10-22

function s = im_eval ()

s1 = sig_gen('lo', 'sine', [0 500], [0.0 1]);
s2 = sig_gen('s1', 'sine', [0 100 500 900 1400], [0.0 0.5 1.0 0.5 0.25]);

s = modulate(s1, s2);

close all;
plotSig(s);
function s = sig_gen(name, type, freq, amp)

peaks = [];
switch type
	case 'sine'
		f = freq;
		a = amp;
	case 'rect'
		N = 10;
		f = [];
		a = [];
		k = 1;
		for n=1:N
			f = [f k*freq];
			a = [a amp/k];
			k = k + 2;
		end
endswitch
	
s = struct('name', name, 'f', f, 'a', a);
endfunction

function m = modulate(s1, s2)

m = struct('name', sprintf("%s x %s", s1.name, s2.name), 'f', [], 'a', []);

f = [];
a = [];

for i=1:length(s1.f)
	for j=1:length(s2.f)
		f1 = s1.f(i) - s2.f(j);
		f2 = s1.f(i) + s2.f(j);
		a = s1.a(i) * s2.a(j);
		
		m = addFreq(m, f1, a);
		m = addFreq(m, f2, a);
	end
end

endfunction

function x = addFreq(x, f, a)

found = 0;
for i=1: length(x.f)
	if (x.f(i) == f)
		found = i;
		break;
	end
end
if (found > 0)
	x.a(found) = x.a(found) + a;
elseif a ~= 0
	x.f = [x.f f];
	x.a = [x.a a];
end

endfunction

function plotSig(s)
	stem(s.f, s.a, 'baseline', -10); grid; legend(s.name)
endfunction
	
endfunction