The code overwrites dif_x in each iteration. Maybe you want to collect the different matrices instead:
theta = [ 45 46 48] ;
t = [ 1 2 3 ];
r = [200 210 220];
dif_x = zeros(2, 3, 3); % Pre-allocation
for i=1:3
dif_x(:, :, i) = [-cos(theta(i)), r(i).*sin(theta(i)), 2*a.*t(i)+b;...
-sin(theta(i)), -r(i).*cos(theta(i)), 2*p.*t(i)+q];
end
It is safer to separate the elements of arrays by commas.
