Ensuring periodicity of the Green's function

This formulation avoids redundant calculations and ensures T-periodicity of the Green's function for the grid defined over the interval [-T, T]
- With the previous formulation, in the highly over-damped cases, we obtained NaN expressions when evaluating the Green's function for negative values of t.

@SSR/update_Jvec.m

@@ -1,5 +1,9 @@
 function update_Jvec(O)
-t1 = -O.T:O.dt:O.T; % padding Green's function to ensure correct convolution
-O.Jvec = J(O,t1,O.T);
+% Computing Green's function over grid [0,T]
+J1 = J(O,O.t,O.T);
+% Padding Green's function, i.e., using values over grid [-T,T] 
+% to ensure correct convolution (using the fact that the Green's function 
+% is T periodic) 
+O.Jvec = [J1(:,1:end-1) J1];
 O.isupdated.J = true;
 end

@SSR/update_Lvec.m

@@ -1,5 +1,9 @@
 function update_Lvec(O)
-t1 = -O.T:O.dt:O.T; % padding Green's function to ensure correct convolution
-O.Lvec = L(O,t1,O.T);
+% Computing Green's function over grid [0,T]
+L1 = L(O,O.t,O.T);
+% Padding Green's function, i.e., using values over grid [-T,T] 
+% to ensure correct convolution (using the fact that Green's function 
+% is T periodic) 
+O.Lvec = [L1(:,1:end-1) L1];
 O.isupdated.L = true;
 end