well am confuse because of my scheme which is 

(1-3r)U[i-1,j+1] +2(2-3r)U[i,j+1] +(1-3r)U[i+1,j+1]= (1+3r)U[i-1,j] +2(2+3r)U[i,j] +(1+3r)U[i+1,j]

now problem here is coefficients with U.. they are not similar on both sides so please can u let me know code about this...now here how can i generate matrix of oder n x n using this scheme...thanks

hi frndz...i want to generate a matrix of order n x n in maple through loops..for example if equation is 
rUi-1,j+1 -2rUi,j+1 +rUi+1,j+1 = rUi-1,j -2rUi,j +rUi+1,j

then how to write code that it generates n x n matrix for above equation if at jth level values are known and j+1 level vaules are unknown...