for i = [30 45]
	p = dlmread(sprintf('products/p%03d', i), ' ');

	day = p(:,3);
	quantity = p(:,4);

	middle = repmat(mean(p(:,4)), 42, 1);
	middle_20 = repmat(mean(p(1:20, 4)), 42, 1);

	[m, n] = regress(day, quantity);
	f = @(x) m .* x + n;

	[m, n] = regress(day(1:20), quantity(1:20));
	g = @(x) m .* x + n;

	figure
	plot(p(:,4),    "-;quantity;",
	     middle,    "-;Mittelwert;",
	     middle_20, "-;Mittelwert 1-20;",
	     f(day),    "-or;Regression 1-42;",
	     g(day),    "-om;Regression 1-20;")

endfor