Xi = e7yJ{'/^(I,J+2)e(J+J)[(Hi/D(I,J+J))-(Hi/D(I,J))] 



+i/^(I-J,J)e(J-J)[(Hi/D(I,J))-(Hi/D(I,J-J))]}. (65) 



Note that the values of all the field variables at previous time 

 steps are used in the expressions of the coupling terms. This 

 implies that the codes for these terms at even time steps are the 

 same as those at odd time steps except for the sequence in which they 

 are applied. Eqs. (65), (64b), and (64a) are the codes employed for 

 implicit computations of V and 4/ and for explicit computations of U, 

 respectively. 



Sequential coding of coupling terms for the implicit and 

 explicit internal mode computations at odd time steps, are 



Xe = -g[eHiH2/D(I,J)]ujjJ{t^(I-J,J)[(Hi/D(I,J))-(H3^/D(l4.J))] 



+xlr^(l,3+^)[{ii;^/D(l+^,3))-(li-^/D(l,3))]], (66a) 



+U^(I+J,J)[(Hi/D(l4.J))-(Hi/D(I,J))]} 

 +i;y{V^(I,J-i^)e(J+J)[(Hi/D(I,J+^))-(Hi/D(I,J))] 

 +V^(I,J-J)e(J-J)[(H;L/°(I,J))-(H;L/D(I,J-J))]}}, and (66b) 



Xe = -g[eHiH2/D(I,J)]i;yJ{\i^(I,J+J)«(J+2)[(Hi/D(I,J+J))) 



-{Hi/D(I,J))]+\i^(I-i,J)e(J-^)[(Hi/D(I,J))-(Hi/D(I,J-J))]}.(67) 



The same considerations for the coding at even time steps as 

 discussed above also apply. 



It is noteworthy that the numerical coding of the coupling terms 

 employed is the only possible form, on the basis of energy transfer, 



32 



